Tag: Structure

  • Understand the Modigliani Miller Proposition with the Capital Structure Theory!

    Understand the Modigliani Miller Proposition with the Capital Structure Theory!

    What is the Modigliani Miller? The Modigliani–Miller theorem is an influential element of economic theory; it forms the basis for modern thinking on capital structure. Modigliani and Miller approach to capital theory, devised in the 1950s advocates capital structure irrelevancy theory. This suggests that the valuation of a firm is irrelevant to the capital structure of a company. So, what is the topic we are going to discuss; Understand the Modigliani Miller Proposition with the Capital Structure Theory!

    Here are explained formula of the Modigliani Miller Proposition for the Capital Structure Theory!

    The capital structure of a company is the way a company finances its assets. A company can finance its operations by either equity or different combinations of debt and equity. The capital structure of a company can have a majority of the debt component or a majority of equity or a mix of both debt and equity. Modigliani and Miller, two professors in the 1950s, studied capital-structure theory intensely. From their analysis, they developed the capital-structure irrelevance proposition.

    Essentially, they hypothesized that in perfect markets, it does not matter what capital structure a company uses to finance its operations. They theorized that the market value of a firm is determined by its earning power and by the risk of its underlying assets and that its value is independent of the way it chooses to finance its investments or distribute dividends.

    Modigliani and Miller’s Capital Structure Irrelevance Proposition:

    The M&M capital-structure irrelevance proposition assumes no taxes and no bankruptcy costs. In this simplified view, the weighted average cost of capital (WACC) should remain constant with changes in the company’s capital structure. For example, no matter how the firm borrows, there will be no tax benefit from interest payments and thus no changes or benefits to the WACC.

    Additionally, since there are no changes or benefits from increases in debt, the capital structure does not influence a company’s stock price, and the capital structure is therefore irrelevant to a company’s stock price. However, as we have stated, taxes and bankruptcy costs do significantly affect a company’s stock price. In additional papers, Modigliani and Miller included both the effect of taxes and bankruptcy costs.

    Modigliani Miller Proposition:

    The following Proposition is two types below are:

    Proposition-I

    The Modigliani-Miller Proposition-I Theory (MM-I) states that under a certain market price process, in the absence of taxes, no transaction costs, no asymmetric information and in a perfect market, the cost of capital and the value of the firm are not affected by the change in capital structure. The firm’s value is determined by its real assets, not by the securities it issues. In other words, capital structure decisions are irrelevant as long as the firm’s investment decisions are taken as given.

    The Modigliani and Miller explained the theorem was originally proven under the assumption of no taxes. It is made up of two propositions that are (i) the overall cost of capital and the value of the firm are independent of the capital structure. The total market value of the firm is given by capitalizing the expected net operating income by the rate appropriate for that risk class. (ii) The financial risk increase with more debt content in the capital structure. As a result, the cost of equity increases in a manner to offset exactly the low-cost advantage of debt. Hence, the overall cost of capital remains the same.

    The assumptions of the MM theory are:

    1. There is a perfect capital market. Capital markets are perfect when: 1) Investors are free to buy and sell securities. 2) Investors can trade without restrictions and can borrow or lend funds on the same terms as the firms do. 3) Investors behave rationally. 4) Investors have equal access to all relevant information. 5) Capital markets are efficient. 6) No costs of financial distress and liquidation, and 7) There are no taxes.
    2. Firms can be classified into homogeneous business risk classes. All the firms in the same risk class will have the same degree of financial risk.
    3. All investors have the same view for the investment, profits, and dividends in the future; they have the same expectation of a firm’s net operating income.
    4. The dividend payout ratio is 100%, which means there are no retained earnings.

    In the absence of the tax world, base on MM Proposition-I, the value of the firm is unaffected by its capital structure. In other words, regardless of whether a company has liabilities, the total risk of its securities holders will not change even the capital structure is changed. As the weighted average cost of capital unchanged, so must the same as the total value of the company.  That is VL = VU = EBIT/equity, where VL is the value of a levered firm = price of buying a firm that is composed of some mix of debt and equity, VU is the value of an unlevered firm = the price of buying a firm composed only of equity and EBIT is earnings before interest and tax. Whether or not the company has loans or the loans for high or low, investors are all accessible through the following two kinds of investment on their own to create the desired type of earning.

    1. Direct investments in the company’s stock borrowing
    2. If shares of levered firms are priced too high, investors will try to take advantage of borrowing on their own and use the money to buy shares in unlevered firms. The use of debt by the investors is known as homemade leverage.

    The investors of homemade leverage can obtain the same return as the levered firms, therefore, for investors; the value of the firm is not affected by the debt-equity mix.

    The MM Proposition I assumptions are quite unrealistic, there have some implications,

    1. Capital structure is irrelevant to shareholder wealth maximization.
    2. The value of the firm is determined by the firm’s capital budgeting decisions.
    3. Increasing the extent to which a firm relies on debt increases both the risk and the expected return to equity – but not the price per share.

    Based on the inadequate of MM Proposition-I, Franco Modigliani and Merton H.Miller revised their theory in 1963, which is MM Proposition-II.

    Proposition-II

    The Modigliani-Miller Proposition II Theory (MM II) defines the cost of equity is a linear function of the firm’s debt/equity ratio. According to them, for any firm in a given risk class, the cost of equity is equal to the constant average cost of capital plus a premium for the financial risk, which is equal to debt/equity ratio times the spread between average cost and cost of debt. Also, Modigliani and Miller recognized the importance of the existence of corporate taxes.

    Accordingly, they agreed that the value of the firm will increase or the cost of capital will decrease with the use of debt due to tax deductibility of interest charges. Thus, the value of the corporation can be achieved by maximizing debt component in the capital structure. This theory of capital structure for the study provided an important and analytical framework. According to this approach, value of a firm is VL = VU = EBIT (1-T) / equity + TD where TD is tax savings. MM Proposition II is assuming that the tax shield effect of each is the same, and continued insight.

    Leverage firms are increased in interest expense due to reduced tax liability, has also increased the allocation to the shareholders and creditors of the cash flow. The above formula can be deduced from the company debt the more the greater the tax saving benefits, the greater the value of the company. The revised capital structure of the MM Proposition-II pointed out that the existence of tax shield in a perfect capital market conditions cannot be reached, in an imperfect financial market, the capital structure changes will affect the company’s value.

    Therefore, the value and cost of capital of the corporation with the capital structure changes in different leverage, the value of the levered firm will exceed the value of the unlevered firm. MM Proposition theory suggests that the higher the debt ratio is more favorable to corporate, but through borrowing adds an interest tax shield it may lead to costs of financial distress. Financial distress occurs when promises to creditors are broken or honored with difficulty.

    Financial distress may lead to bankruptcy. The trade-off theory of capital structure theory in MM based on the added risk of bankruptcy and further improves the capital structure theory, to make it more practical significance. A firm that follows the trade-off theory sets a target debt to value ratio and then gradually moves towards the target. The target is determined by balancing the tax benefits of using debt against the costs of financial distress that rise at an increasing rate with the use of leverage.

    It so predicts the moderate amount of debt as optimal. But there is evidence that the most profitable firm in an industry tend to borrow the least, while their probability of entering in financial distress seems to be very low. This fact contradicts the theory because if the distress risk is low, an increase in debt has a favorable tax effect. Under the trade-off theory, high profits should mean more debt-servicing capacity and more taxable income to shield and therefore should result in a higher debt ratio.

    Understand the Modigliani Miller Proposition with the Capital Structure Theory
    Understand the Modigliani Miller Proposition with the Capital Structure Theory! Image credit from #Pixabay.

    Understand the Capital Structure Decision in Corporate Finance:

    Corporate finance is a specific area of finance dealing with the financial decisions corporations make and the tools as well as analysis used to make these decisions. The discipline as a whole may be divided among long-term and short-term decisions and techniques with the primary goal being maximizing corporate value while managing the firm’s financial risks. Capital investment decisions are long-term choices that investment with equity or debt, and the short-term decisions deal with the balance of current assets and current liabilities which is managing cash, inventories, and short-term borrowing and lending.

    Corporate finance can be defined as the theory, process, and techniques that corporations use to make the investment, financing and dividend decisions that ultimately contribute to maximizing corporate value. Thus, a corporation will first decide in which projects to invest, then it will figure out how to finance them, and finally, it will decide how much money, if any, to give back to the owners. All these three dimensions which are investing, financing and distributing dividends are interrelated and mutually dependent. The capital structure decision is one of the most fundamental issues in corporate finance.

    The capital structure of a company refers to a combination of debt, preferred stock, and common stock of finance that it uses to fund its long-term financing. Equity and debt capital are the two major sources of long-term funds for a firm. The theory of capital structure is closely related to the firm’s cost of capital. As the enterprises to obtain funds need to pay some costs, the cost of capital in the investment activities is also the main consideration of the rate of return.

    The weighted average cost of capital (WACC) is the expected rate of return on the market value of all of the firm’s securities. WACC depends on the mix of different securities in the capital structure; a change in the mix of different securities in the capital structure will cause a change in the WACC. Thus, there will be a mix of different securities in the capital structure at which WACC will be the least.

    The decision regarding the capital structure is based on the objective of achieving the maximization of shareholders wealth. With regard to the capital structure of the theoretical basis, the most well-known theory is Modigliani-Miller theorem of Franco Modigliani and Merton H.Miller. Yet the seemingly simple question as to how firms should best finance their fixed assets remains a contentious issue.

    The Designing an Optimal Capital Structure:

    The optimal capital structure refers to a proportion of debt and equity at which the marginal real cost of each available source of financing is the same. This is also viewed as a capital structure that maximizes the market price of shares and minimizes the overall cost of capital of the firm. Theoretically, the concept of optimal capital structure can easily be explained, but in operational terms, it is difficult to design an optimal capital structure because of a number of factors, both quantitative and qualitative, that influence the optimum capital structure. Moreover, the subjective judgment of the finance manager of the firm is also an influencing factor in designing the optimum capital structure of a firm. Designing the capital structure is also known as capital structure planning and capital structure decision.

  • What is Organizational Structure for Corporate Entrepreneurship?

    What is Organizational Structure for Corporate Entrepreneurship?

    An organizational structure defines how activities such as task allocation, coordination, and supervision are directed toward the achievement of organizational aims. Also learn, Why is Intrapreneurship Better than Entrepreneurship? This article explains to Organizational Structure for Corporate Entrepreneurship. Organizations need to be efficient, flexible, innovative and caring to achieve sustainable competitive advantage. Organizational structure can also consider as the viewing glass or perspective through which individuals see their organization and its environment.

    Learn, Entrepreneurial, What is Organizational Structure for Corporate Entrepreneurship?

    Corporate entrepreneurship (also called intrapreneurship) is defined by Guth and Ginsburg as;

    “The birth of new business within existing organizations, that is, internal innovation or venturing; and the transformation of organizations through the renewal of the key ideas on which they are built, that is, strategic renewal.”

    The organizational structure affects organizational action in two ways:
    1. It provides the foundation on which standard operating procedures and routines rest.
    2. It determines which individuals get to participate in which decision-making processes, and thus to what extent their views shape the organization’s actions.

    Organizational Structures for Corporate Entrepreneurship:

    Burgelman proposes that the use of a particular organizational structure should determine by:

    1. The strategic importance of the new business to the corporation. and.
    2. The relatedness of the unit’s operations to those of the corporation.

    The combination of these two factors results in nine organizational structures for corporate entrepreneurship.

    1] Direct Integration:

    A new business with a great deal of strategic importance and operational relatedness must be a part of the corporation’s mainstream. Product champion-people who are respected by others in the corporation and who know how to work the system need to manage these projects.

    2] New Product Business Department:

    A new business with a great deal of strategic importance and partial operational relatedness should be a separate department. Organize around an entrepreneurial project in the division where skills and capabilities can share.

    3] Special Business Units:

    A new business with a great deal of strategic importance and low operational relatedness should be a special new business unit with specific objectives and time horizons.

    4] Micro New Ventures Department:

    A new business with uncertain strategic importance and high operational relatedness should be a peripheral project. Which is likely to emerge in the operating divisions continuously. Each division thus has its new ventures department.

    5] New Venture Division:

    A new business with the uncertain strategic importance that is only partly related to present corporate operations belongs in a new venture division. It brings together projects that either exists in various parts of the corporation or can acquire externally, sizable new businesses are built.

    6] Independent Business Units:

    Uncertain strategic importance coupled with no relationship to present corporate activities can make external arrangements attractive. Also read, The Corporate Entrepreneurship Categories and Organizational Thinking.

    7] Nurturing and Contracting:

    When an entrepreneurial proposal might not be important strategically to the corporation but is strongly related to present operations. Top management might help the entrepreneurial unit to spin-off from the corporation. This allows a friendly competitor, instead of one of the corporation’s major rivals, to capture a small niche.

    8] Contracting:

    As the required capabilities and sills of the new business are less related to those of the corporation. The parent corporation may spin off the strategically unimportant unit yet keep some relationship through a contractual arrangement with the new firm. The connection s useful in case the new firm eventually develops something of value to the corporation.

    9] Complete Spin-Off:

    If both the strategic importance and the operational relatedness of the new business are negligible. The corporations are likely to completely sell off the business to another firm or the present employees in some form of ESOP (Employee Stock Ownership Plan). The corporation also could sell off the unit through a leveraged buy-out executives of the unit buy. Also, the unit from the parent company with money from a third source, to be repaid out of the unit’s anticipated earnings.

    Entrepreneurial Organizational Structure:

    The organizational structure of an entrepreneurial company often has two central requirements based on the nature and size of the business. Because they are innovators, these businesses must develop organizational structures. That promotes frequent interaction and communication among their marketing, sales and production departments. Because they are often smaller businesses that aren’t able to fully departmentalize because they have large sales of one product. They must maximize their management resources through multitasking.

    1] Theory Originator:

    The theory of an entrepreneurial organizational structure was developing by McGill University professor and management expert Henry Mintzberg. He proposed theories about five different types of organizational structures, including one well suited for operating an entrepreneurial organization. Others have since expanded on his theories, first proposed in the 1970s, as markets and technologies have evolved.

    2] Flat vs Hierarchical Structure:

    Smaller businesses with few employees that continue to evolve. Their product development and marketing often use a flat organizational structure rather than a hierarchical one. A traditional hierarchical organizational structure organizes a company based on departments. With each department having a leader and subordinates reporting to the department head.

    These departments work independently, reporting to a president, chief executive officer or executive management team. A flat organizational structure consists of individuals or small groups that work collaboratively, all reporting to the owner or CEO. A flat structure can require managers to take on or participate in more than one task to maximize scarce human resources.

    3] Planning Structure:

    An entrepreneurial structure should facilitate cooperative planning rather than top-down strategic and marketing planning. Which features execution of plans assigned to different departments. Marketing activities include product development, pricing strategies, brand creation, and distribution channel selection that occur before any promotions take place.

    For example, at a larger business with a hierarchical organizational structure. Also, the marketing department might develop the product and then tell the production department to determine how to make it. In an entrepreneurial organization, all team members are involving in product planning.

    So, they can share their concerns or make suggestions about whether they can make the product. At large companies, marketing will know the capabilities of its production department. While at an entrepreneurial company, marketing will pitch an idea, asking production. Information technology, sales, and finance if they can bring the idea to market.

    4] Communication Structure:

    An entrepreneurial organization holds regular team meetings to discuss ideas before a decision is creating. While a more traditional organizational structure uses meetings of department heads to announce their progress and tell subordinates what has been deciding. An entrepreneurial company might create an intranet or a communication system based on the Cloud to exchange project status in real-time.

    A Cloud-based system puts information on a secure Internet site that people can access with a password from anywhere. An intranet resides on a company’s servers. Using such a system, each team member will have his responsibilities but will update his progress on a master document that all other team members can access from their computers at any time of the day.

    What is Organizational Structure for Corporate Entrepreneurship
    What is Organizational Structure for Corporate Entrepreneurship? Google Image Searching.

    Reference:

    1. Structures – //www.mbaknol.com/strategic-management/corporate-entrepreneurship/
    2. Entrepreneurial – //yourbusiness.azcentral.com/entrepreneurial-organizational-structure-16071.html
    3. Photo Credit URL – //conditionaldesign.org/workshops/3d-straw-structure/resources/09-img-5455-edit.jpg

  • What are Effects of Goal Orientation on Student Achievement?

    What are Effects of Goal Orientation on Student Achievement?

    The extent to which students have a learning or performance goal orientation is associated with a variety of student behaviors and beliefs. These have been divided into cognitive strategies and engagement and motivational beliefs and actions.

    Cognitive Strategies and Engagement

    Learning goals foster cognitive engagement and effort (Meece, Blumenfeld, & Hoyle, 1988). Fifth- and sixth-grade science students who placed greater emphasis on learning goals also reported more active cognitive engagement. Students with performance goals (pleasing the teacher or seeking social recognition) had a lower level of cognitive engagement. Wolters, Yu, and Pintrich (1996) found that task value and interest were related to learning goals. The use of cognitive strategies and information processing is related to goal orientations of students at different levels of schooling. Learning that is potentially more meaningful or complex, requiring deep-level processing, appears to be the most vulnerable to the negative effects of performance goals (Graham & Golan, 1991). When the emphasis was on ability, as in the performance goal situation, there was interference with memory for tasks that required a great deal of cognitive effort. Performance goals also undermined the problem-solving strategies of children (Elliott & Dweck, 1988). In contrast, learning goals were the strongest predictor of seventh- and eighth-grade students’ cognitive strategy use (Wolters et al., 1996). These goals were also predictive of deep processing, persistence, effort, and exam performance of college students (Elliot, McGregor, & Gable, 1999).

    Motivational Beliefs and Actions

    The particular goal orientation affects motivation beliefs such as the role of effort in learning, self-efficacy beliefs, the tendency to use self-handicapping strategies, help seeking, and helpless patterns.

    Self-Efficacy: A learning goal orientation was generally found to be associated with higher self-efficacy. Wolters et al. (1996) reported that seventh- and eighth-grade students who reported greater endorsement of a learning goal also tended to report higher levels of self-efficacy. Learning goals were also positively related to self-efficacy in the subjects of writing and science (Pajares, Britner, & Valiante, 2000). In contrast, performance goals were related to low self-efficacy (Pintrich, Zusho, Schiefele, & Pekrun, 2001).

    Self-Handicapping: Self-handicapping strategies, such as low effort, are associated with performance goals (Midgley & Urden, 2001). Elliott and Dweck (1988) found that children with performance goals were more likely to avoid challenge and exhibit low persistence. These strategies undermine student achievement. Another type of self-handicapping strategy associated with performance goals is cheating (Anderman, Griesinger, & Westerfield, 1998). The authors explained that, by cheating, not only do students protect themselves against perceptions of low ability, they improve their grades.

    Help Seeking: The particular goal orientation was also found to influence help-seeking behaviors (Butler & Neuman, 1995). Second- and sixth-grade students were more likely to seek help when the task was presented to them as an opportunity to develop competence. When tasks were presented to students as a measure of their ability, they were less likely to seek help. Students were more likely to seek help in classrooms with a learning goal focus and to avoid help seeking in a performance goal structure (Butler & Neuman, 1995; Ryan, Gheen, & Midgley, 1998).

    Helpless Patterns: Finally, one of the most debilitating effects of performance goals is the vulnerability to helpless patterns (Dweck, 1986). Goals that focus students on using performances to judge their ability can make them vulnerable to a helpless pattern in the face of failure (Dweck & Sorich, 1999; Heyman & Dweck, 1992; Midgley et al., 2001).

    In conclusion, performance goal beliefs are generally seen as the most maladaptive pattern as students are more extrinsically motivated, focused on outcome and not on learning (C. Ames, 1992), and focused on being superior to others (Nicholls, 1990). At the same time, there is continued agreement that the learning goal pattern is the more adaptive one, fostering long-term achievement that reflects intrinsic motivation (C. Ames, 1992; Heyman & Dweck, 1992; Kaplan & Middleton, 2002; Meece, 1991; Midgley et al., 2001). As Kaplan and Middleton asked, “Should childhood be a journey or a race?”

  • DNA Structure

    What is DNA Structure?

    What do a human, a rose, and a bacterium have in common? Each of these things along with every other organism on Earth contains the molecular instructions for life, called deoxyribonucleic acid or DNA. Encoded within this DNA (Deoxyribonucleic Acid) are the directions for traits as diverse as the color of a person’s eyes, the scent of a rose, and the way in which bacteria infect a lung cell.

    DNA is found in nearly all living cells. However, its exact location within a cell depends on whether that cell possesses a special membrane-bound organelle called a nucleus. Organisms composed of cells that contain nuclei are classified as eukaryotes, whereas organisms composed of cells that lack nuclei are classified as prokaryotes. In eukaryotes, DNA is housed within the nucleus, but in prokaryotes, DNA is located directly within the cellular cytoplasm, as there is no nucleus available.

    But what, exactly, is DNA? In short, DNA is a complex molecule that consists of many components, a portion of which are passed from parent organisms to their offspring during the process of reproduction. Although each organism’s DNA is unique, all DNA is composed of the same nitrogen-based molecules. So how does DNA differ from organism to organism? It is simply the order in which these smaller molecules are arranged that differs among individuals. In turn, this pattern of arrangement ultimately determines each organism’s unique characteristics, thanks to another set of molecules that “read” the pattern and stimulate the chemical and physical processes it calls for.

    DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group, and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA’s instructions, or genetic code. Similar to the way the order of letters in the alphabet can be used to form a word, the order of nitrogen bases in a DNA sequence forms genes, which in the language of the cell, tells cells how to make proteins. Another type of nucleic acid, ribonucleic acid, or RNA, translates genetic information from DNA into proteins.

    The entire human genome contains about 3 billion bases and about 20,000 genes. Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If you think of the double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine.

    DNA molecules are long so long, in fact, that they can’t fit into cells without the right packaging. To fit inside cells, DNA is coiled tightly to form structures we call chromosomes. Each chromosome contains a single DNA molecule. Humans have 23 pairs of chromosomes, which are found inside the cell’s nucleus.

    Why does a DNA molecule consist of two strands? The primary function of DNA is to store and transmit genetic information. To accomplish this function DNA must have two properties. It must be chemically stable so as to reduce the possibility of damage. DNA must also be capable of copying the information it contains. The two-stranded structure of DNA gives it both of these properties. The nucleotide sequence contains the information found in DNA. The nucleotides connect the two strands through hydrogen bonds. Because each nucleotide has a unique complementary nucleotide, each strand contains all the information required to synthesize a new DNA molecule. The double-stranded structure also makes the molecule more stable.

    DNA is the information molecule. It stores instructions for making other large molecules, called proteins. These instructions are stored inside each of your cells, distributed among 46 long structures called chromosomes. These chromosomes are made up of thousands of shorter segments of DNA, called genes. Each gene stores the directions for making protein fragments, whole proteins, or multiple specific proteins.

    DNA is well-suited to perform this biological function because of its molecular structure, and because of the development of a series of high-performance enzymes that are fine-tuned to interact with this molecular structure in specific ways. The match between DNA structure and the activities of these enzymes is so effective and well-refined that DNA has become, over evolutionary time, the universal information-storage molecule for all forms of life. Nature has yet to find a better solution than DNA for storing, expressing, and passing along instructions for making proteins.

    Alternative DNA structures

    DNA Structure A-DNA B-DNA and Z-DNA
    DNA Structure A-DNA B-DNA and Z-DNA

    DNA (Deoxyribonucleic Acid) exists in many possible conformations that include A-DNA, B-DNA, and Z-DNA forms, although, only B-DNA and Z-DNA have been directly observed in functional organisms. The conformation that DNA adopts depends on the hydration level, DNA sequence, the amount and direction of supercoiling, chemical modifications of the bases, the type and concentration of metal ions, and the presence of polyamines in solution.

    The first published reports of A-DNA X-ray diffraction patterns—and also B-DNA—used analyses based on Patterson transforms that provided only a limited amount of structural information for oriented fibers of DNA. An alternative analysis was then proposed by Wilkins et al., in 1953, for the in vivo B-DNA X-ray diffraction scattering patterns of highly hydrated DNA fibers in terms of squares of Bessel functions. In the same journal, James Watson and Francis Crick presented their molecular modeling analysis of the DNA X-ray diffraction patterns to suggest that the structure was a double-helix.

    Although the B-DNA form is most common under the conditions found in cells, it is not a well-defined conformation but a family of related DNA conformations that occur at the high hydration levels present in living cells. Their corresponding X-ray diffraction and scattering patterns are characteristic of molecular para crystals with a significant degree of disorder.

    Compared to B-DNA, the A-DNA form is a wider right-handed spiral, with a shallow, wide minor groove and a narrower, deeper major groove. The A form occurs under non-physiological conditions in partly dehydrated samples of DNA, while in the cell it may be produced in hybrid pairings of DNA and RNA strands, and in enzyme-DNA complexes. Segments of DNA where the bases have been chemically modified by methylation may undergo a larger change in conformation and adopt the Z form. Here, the strands turn about the helical axis in a left-handed spiral, the opposite of the more common B form. These unusual structures can be recognized by specific Z-DNA binding proteins and may be involved in the regulation of transcription.

  • LNA (Locked Nucleic Acid)

    LNA (Locked Nucleic Acid)

    What is an LNA? A locked nucleic acid (LNA), often referred to as inaccessible RNA, is a modified RNA nucleotide. The ribose moiety of an LNA nucleotide is modified with an extra bridge connecting the 2′ oxygen and 4′ carbon. The bridge “locks” the ribose in the 3′-endo (North) conformation, which is often found in the A-form duplexes. LNA nucleotides can be mixed with DNA or RNA residues in the oligonucleotide whenever desired and hybridize with DNA or RNA according to Watson-Crick base-pairing rules. Such oligomers are synthesized chemically and are commercially available. The locked ribose conformation enhances base stacking and backbone pre-organization. This significantly increases the hybridization properties (melting temperature) of oligonucleotides. LNA was independently synthesized by the group of Jesper Wengel in 1998, soon after the first synthesis by the group of Takeshi Imanishi in 1997. The exclusive rights to the LNA technology were secured in 1997 by Exiqon A/S, a Danish biotech company.

    LNA nucleotides are used to increase the sensitivity and specificity of expression in DNA microarrays, FISH probes, quantitative PCR probes and other molecular biology techniques based on oligonucleotides. For the in situ detection of miRNA, the use of LNA is currently (2005) the only efficient method. A triplet of LNA nucleotides surrounding a single-base mismatch site maximizes LNA probe specificity unless the probe contains the guanine base of G-T mismatch.

    Using LNA-based oligonucleotides therapeutically is an emerging field of biotechnology. The Danish pharmaceutical company Santaris Pharma a/s owns the sole rights to therapeutic uses of LNA technology and is now developing a new, LNA-based, hepatitis C drug called miravirsen, targeting miR-122, which is in Phase II clinical testing as of late 2010.

    Definition of an LNA?

    Locked nucleic acid (LNA) is a nucleic acid analogue containing one or more LNA nucleotide monomers with a bicyclic furanose unit locked in an RNA mimicking sugar conformation. LNA oligonucleotides display unprecedented hybridization affinity toward complementary single-stranded RNA and complementary single- or double-stranded DNA. Structural studies have shown that LNA oligonucleotides induce A-type (RNA-like) duplex conformations. The wide applicability of LNA oligonucleotides for gene silencing and their use for research and diagnostic purposes are documented in a number of recent reports, some of which are described herein.

    LNA Locked Nucleic Acid analogues

    What is an LNA?

    LNA (Locked Nucleic Acids) are synthetic modified nucleic acids where the carbohydrate part of the nucleic acid has been synthetically changed. The modification results in an increased bonding strength between the DNA-bases in a double-helix when one of the DNA-bases has been modified. The overall result is a higher melting point of a DNA double-helix containing LNA-modified nucleic acids and thereby an increased stability. By designing the complementary DNA-strand in a double helix so it consists more or less of LNA-units, it is possible to regulate the rate of transcription – even to block it completely. In this way, it is possible to control the expression of genes and thereby the synthesis of selected proteins. The LNA technology is, therefore, a promising tool in the treatment of diseases which originate from genetic defects.

  • RNA (Ribonucleic Acid)

    RNA (Ribonucleic Acid)

    Ribonucleic Acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation, and expression of genes. RNA and DNA are nucleic acids, and, along with proteins and carbohydrates, constitute the four major macromolecules essential for all known forms of life. Like DNA, RNA is assembled as a chain of nucleotides, but unlike DNA it is more often found in nature as a single-strand folded onto itself, rather than a paired double-strand. Cellular organisms use messenger RNA (mRNA) to convey genetic information (using the letters G, U, A, and C to denote the nitrogenous bases guanine, uracil, adenine, and cytosine) that directs the synthesis of specific proteins. Many viruses encode their genetic information using an RNA genome.

    Some RNA molecules play an active role within cells by catalyzing biological reactions, controlling gene expression, or sensing and communicating responses to cellular signals. One of these active processes is protein synthesis, a universal function where RNA molecules direct the assembly of proteins on ribosomes. This process uses transfer RNA (tRNA) molecules to deliver amino acids to the ribosome, where ribosomal RNA (rRNA) then links amino acids together to form proteins.

    Ribonucleic acid is a linear molecule composed of four types of smaller molecules called ribonucleotide bases: adenine (A), cytosine (C), guanine (G), and uracil (U). RNA is often compared to a copy from a reference book, or a template, because it carries the same information as its DNA template but is not used for long-term storage.

    Each ribonucleotide base consists of a ribose sugar, a phosphate group, and a nitrogenous base. Adjacent ribose nucleotide bases are chemically attached to one another in a chain via chemical bonds called phosphodiester bonds. Unlike DNA, RNA is usually single-stranded. Additionally, RNA contains ribose sugars rather than deoxyribose sugars, which makes RNA more unstable and more prone to degradation.

    RNA is synthesized from DNA by an enzyme known as RNA polymerase during a process called transcription. The new RNA sequences are complementary to their DNA template, rather than being identical copies of the template. RNA is then translated into proteins by structures called ribosomes. There are three types of RNA involved in the translation process: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

    Although some RNA molecules are passive copies of DNA, many plays crucial, active roles in the cell. For example, some RNA molecules are involved in switching genes on and off, and other RNA molecules make up the critical protein synthesis machinery in ribosomes.

    “Research on RNA has led to many important biological discoveries and numerous Nobel Prizes. Nucleic acids were discovered in 1868 by Friedrich Miescher, who called the material ‘nuclein’ since it was found in the nucleus. It was later discovered that prokaryotic cells, which do not have a nucleus, also contain nucleic acids. The role of RNA in protein synthesis was suspected already in 1939. Severo Ochoa won the 1959 Nobel Prize in Medicine (shared with Arthur Kornberg) after he discovered an enzyme that can synthesize RNA in the laboratory. However, the enzyme discovered by Ochoa (polynucleotide phosphorylase) was later shown to be responsible for RNA degradation, not RNA synthesis. In 1956 Alex Rich and David Davies hybridized two separate strands of RNA to form the first crystal of RNA whose structure could be determined by X-ray crystallography.”

    What is meaning of RNA?

    Ribonucleic acid, a nucleic acid present in all living cells. Its principal role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins, although in some viruses RNA rather than DNA carries the genetic information.

    What is Definition of RNA?

    RNA

    RNA is a Ribonucleic Acid and is same copy of DNA (Deoxyribonucleic Acid).

    What is RNA?

    Ribonucleic acid or RNA is one of the three major biological macromolecules that are essential for all known forms of life (along with DNA and proteins). A central tenet of molecular biology states that the flow of genetic information in a cell is from DNA through RNA to proteins: “DNA makes RNA makes protein”. Proteins are the workhorses of the cell; they play leading roles in the cell as enzymes, as structural components, and in cell signaling, to name just a few. DNA (deoxyribonucleic acid) is considered the “blueprint” of the cell; it carries all of the genetic information required for the cell to grow, to take in nutrients, and to propagate. RNA–in this role–is the “DNA photocopy” of the cell. When the cell needs to produce a certain protein, it activates the protein’s gene–the portion of DNA that codes for that protein–and produces multiple copies of that piece of DNA in the form of messenger RNA, or mRNA. The multiple copies of mRNA are then used to translate the genetic code into protein through the action of the cell’s protein manufacturing machinery, the ribosomes. Thus, RNA expands the quantity of a given protein that can be made at one time from one given gene, and it provides an important control point for regulating when and how much protein gets made.

    For many years RNA was believed to have only three major roles in the cell–as a DNA photocopy (mRNA), as a coupler between the genetic code and the protein building blocks (tRNA), and as a structural component of ribosomes (rRNA). In recent years, however, we have begun to realize that the roles adopted by RNA are much broader and much more interesting. We now know that RNA can also act as enzymes (called ribozymes) to speed chemical reactions. In a number of clinically important virus’s RNA, rather than DNA, carries the viral genetic information. RNA also plays an important role in regulating cellular processes–from cell division, differentiation and growth to cell aging and death. Defects in certain RNAs or the regulation of RNAs have been implicated in a number of important human diseases, including heart disease, some cancers, stroke, and many others.

  • DNA (Deoxyribonucleic Acid)

    DNA (Deoxyribonucleic Acid)

    Deoxyribonucleic Acid (DNA) is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids; alongside proteins, lipids and complex carbohydrates (polysaccharides), they are one of the four major types of macromolecules that are essential for all known forms of life. Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. DNA Structure, History of DNA Research.

    What is DNA?

    We all know that elephants only give birth to little elephants, giraffes to giraffes, dogs to dogs and so on for every type of living creature. But why is this so? The answer lies in a molecule called deoxyribonucleic acid (DNA), which contains the biological instructions that make each species unique. DNA, along with the instructions it contains, is passed from adult organisms to their offspring during reproduction. History of DNA Research.

    What is meaning of DNA?

    DNA stands for deoxyribonucleic acid, sometimes called “the molecule of life,” as almost all organisms have their genetic material codified as DNA. Since each person’s DNA is unique, “DNA typing” is a valuable tool in connecting suspects to crime scenes. You can also use the word less scientifically, as in “it’s just not in my DNA to sit through six hours of meetings.”

    You got your DNA from your parents, we call it ‘hereditary material’ (information that is passed on to the next generation). Nobody else in the world will have DNA the same as you, unless you have an identical twin. Deoxyribonucleic acid is a large molecule in the shape of a double helix. That’s a bit like a ladder that’s been twisted many times.

    The two DNA strands are termed polynucleotides since they are composed of simpler monomer units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases either cytosine (C), guanine (G), adenine (A), or thymine (T) and a sugar called deoxyribose and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together (according to base pairing rules (A with T, and C with G) with hydrogen bonds to make double-stranded DNA. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon (TTC).

    DNA stores biological information. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information. This information is replicated as and when the two strands separate. A large part of DNA (more than 98% for humans) is non-coding, meaning that these sections do not serve as patterns for protein sequences.

    The two strands of DNA run in opposite directions to each other and are thus anti-parallel. Attached to each sugar is one of four types of nucleobases (informally, bases). It is the sequence of these four nucleobases along the backbone that encodes biological information. RNA strands are created using DNA strands as a template in a process called transcription. Under the genetic code, these RNA strands are translated to specify the sequence of amino acids within proteins in a process called translation.

    Within eukaryotic cells, DNA is organized into long structures called chromosomes. During cell division these chromosomes are duplicated in the process of DNA replication, providing each cell its own complete set of chromosomes. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such as mitochondria or chloroplasts. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the eukaryotic chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.

    DNA was first isolated by Friedrich Miescher in 1869. Its molecular structure was identified by James Watson and Francis Crick in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling who was a post-graduate student of Rosalind Franklin. DNA is used by researchers as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity. The unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials. And also read it DNA Structure, History of DNA Research.

  • What is Master the Art of Scheduling?

    What is Master the Art of Scheduling?

    “Where are you on the schedule?” Develop the ability to predict the amount of time as a sequence of key tasks that a project should take. And yet we all work with software developers who hate the pressure of committing to a schedule because to complete work usually takes “as long as it takes.” But you can’t effectively run a business without the confidence to work toward a schedule.

    When you recognize the value of time management skills, you become the overseer of your life, with your schedule as your command center. Many people think that creating a schedule is as easy as jotting down the time and activity on a piece of paper. However, scheduling is so much more than that.

    A well-planned schedule of everyday tasks is more than just a reminder of what needs to be done. It also allows you to make time for important tasks that are in line with your goals. It makes you become aware of how you spend your time each day. It helps you to recognize areas that need adjustments so that you can achieve balance between your personal life and your profession. So how should you schedule your time each day? What are the tools you need to become a “master scheduler?” Here are the strategies to learn:

    Gather Your Scheduling Tools

    In general, you would need three essential scheduling tools, and these are:

    A daily planner,

    A weekly planner, and

    A monthly planner

    The daily planner helps to keep you on the right track each day. It enables you to concentrate on exactly what tasks need to be done and how much time you have for each.

    The weekly planner serves as your overview of the events planned out for that week as well as the tasks that you need to accomplish. It helps you get to see what is ahead of you, because focusing only on the everyday tasks might cause you to forget about what is in store for tomorrow, or the day after that.

    Now, you might think that you do not need a monthly planner if you have a weekly one. However, it always helps to have all the dates of the month laid out on a single page. This will enable you to see the important dates of that month and plan your week and days around them.

    However, it is possible to keep a monthly planner without the weekly planner. Just make sure that there is enough space for you to jot down your weekly tasks on the monthly planner.

    There are plenty of planners whether digital or printed out there, so choose your layout carefully. Most of the time, you will find that many planners already have daily, weekly, and monthly sections. This is helpful, especially if you want to carry your planner around. Take care not to purchase more than one type of planner, because you would only end up feeling confused as to which one you should write your next set of tasks.

    One suggestion on how to organize your different planners is that you should have a portable daily planner, and a desktop or wall-mounted weekly and/or monthly planner. This is because you will likely need to check your daily planner constantly throughout the day, while you only need to jot things down and review your weekly/monthly planner once a week. A large monthly planner is helpful as well, because you will want to see everything at a single glance.

    Once you have your scheduling tools, the next step is to create a scheduling routine.

    Create a Scheduling Routine

    Do you take time at the end of each day to plan for the following day? If you do not, then now is the best time to build this habit. A master scheduler should set aside a time each day to plan for tomorrow, each week for the week ahead, and each month to review everything and plan for the next month.

    In most cases, it will only take ten to twenty minutes to plan for the following day and thirty minutes to plan for the week and month ahead. However, the time you would invest in planning will save you from many problems in the future.

    After you have set a fixed “scheduling” time, you should then establish a routine on how to schedule your time. Here are the recommended steps:

    1. Time-block non-negotiable appointments

    Certain parts of the day may be out of your control; such as board meetings or dentist appointments. You should secure them all first, otherwise you might end up with overlapping appointments.

    It must be emphasized that you should also time-block the hours when you will be sleeping. Have to establish a fixed sleeping schedule to stay healthy and sharp the following day. Do not rob yourself of sleeping hours by cramming on certain tasks. Instead, focus on planning your day carefully so that you will have time to accomplish them all.

    1. Schedule your Important Tasks

    At this point, you would be able to see the times lots during the day when you do not have anything scheduled yet. If so, then you can refer to your list of priorities to allocate the different tasks into your day, week, or month.

    For example, if your most important task for the day is to write a thousand words for your personal book project, and if you do not have anything scheduled between seven and ten a.m., then you can block this task within this time.

    1. Schedule your Urgent Tasks

    After you have secured the times lots for your important tasks, you should then move on to blocking in the urgent ones. It helps to use a different colored-pen or highlighter to separate the important from the urgent.

    Do not forget to factor in breaks and an allowance in time for emergencies. In other words, you should never time-block one task after another without at least ten minutes of contingency time. This way, you will not be behind schedule in the next task when there was an unexpected extension in the task before it.

    Here is an example:

    •             Important Task —- 7:00 am to 9:00 am
    •             Contingency Time —- 9:00 am to 9:15 am
    •             Urgent Task —- 9:15 am to 11:30 am
    1. Review your schedule and make adjustments if necessary

    Once you have your entire day planned out, you can go back and assess your schedule as a whole. If you notice that you have spread yourself too thin, consider delegating certain tasks to others, rescheduling them, or canceling them altogether. Once you are satisfied with your schedule, the only thing left to do is to take action.

    As with any other skill, it takes constant practice to become better at scheduling and managing your time well. Nevertheless, it takes more than just scheduling and planning to do a great job every day without feeling burned out. That is because you also need to develop an efficient system. Read the post How to Make Establish an Efficient System? to learn more about that.

  • How to Learn of Hone Your Ability to Concentrate?

    How to Learn of Hone Your Ability to Concentrate?

    The ability to concentrate is a skill that becomes stronger over time. Through constant practice, you will be able to concentrate more effectively for an extended period of time. However, if you constantly find it difficult to focus on tasks, or if you find yourself wasting your time on unimportant activities, then you need to address this problem as soon as possible.

    Ability: Human Resource Management; An acquired or natural capacity or talent that enables an individual to perform a particular job or task successfully. See also aptitude. Law; The power to carry out a legal act or satisfy a legal obligation.

    Concentrate: A concentrate is a form of substance which has had the majority of its base component (in the case of a liquid: the solvent) removed. Typically, this will be the removal of water from a solution or suspension, such as the removal of water from fruit juice. One benefit of producing a concentrate is that of a reduction in weight and volume for transportation, as the concentrate can be reconstituted at the time of usage by the addition of the solvent. Completely different to clustered.

    The good news is that there are tested-and-proven tips on how you can concentrate better. Apply the following tips and notice how you will then be able to finish your important tasks on time.

    Eliminate distractions

    Distractions come in all shapes and sizes. It could be the uncomfortable chair you are sitting on, the messy desk you have to work on, or the loud noises from outside. Whatever your case may be, it is important to get rid of them before you begin your task. That way, you can no longer use them as an excuse to procrastinate.

    Here are some suggestions:

    I. Hang up a “do not disturb” sign.

    II. Play instrumental “concentration enhancing” music to drown out the background noise.

    III. Set your phone on silent mode and store it away.

    IV. Block certain websites that keep you from focusing.

    Focus on one task at a time

    Multi-tasking keeps you from being able to provide quality output. It also stresses your mind out, whether you are aware of it or not. This is because you are not really “accomplishing” multiple things at once, but rather you are rapidly switching from one task to another.

    Instead, set aside a time block for a particular task and do absolutely nothing else except that task within that time frame. You could even set a timer so that you will not have to glance at the clock every now and then to check how much time you have left.

    Take short breaks between tasks

    Most people – even the most productive ones out there – can concentrate on an important task for no more than two hours at a time. Likewise, it takes approximately fifteen minutes of rest to replenish this concentration “energy.” Therefore, you can use this as a rule of thumb to schedule breaks.

    For instance, after working non-stop on a task for two hours straight, set a timer to signal you to take a fifteen-minute break. Then, do something relaxing, such as taking a walk or having a snack. After fifteen minutes, you will be ready to take on another two-hour long task, give or take.

    Focus on challenging tasks during your peak hours

    Identify which part of the day you feel most confident and energized, and use this time to work on the tasks that require the most concentration. For most people, mornings are the times when they feel as if they can handle anything. For others, this happens during the evenings when everyone else is exhausted from work.

    Reward yourself after accomplishing a challenging task

    Our minds are programmed to repeat a certain behavior if we are rewarded for it. Therefore, to condition yourself to practice improving your concentration each day, do not forget to reward yourself after a job well done. It could be something as simple as playing a video game for an hour, watching an episode of your favorite television show, or enjoying a delicious, albeit sinful, snack. That way, you can be more driven to finish the task so that you can get your reward.

    Aside from these tips, it always helps to remind yourself to take good care of your body. Always make it a priority to get enough hours of sleep, eat nutritious meals, and hydrate throughout the day. When your body is healthy and full of energy, it is only natural for your mind to be sharp and focused.

    At this point, you must be excited to start working on your tasks. However, you might want to learn how to manage your schedule first, especially if you have multiple tasks to handle each day. Find out how you can acquire this skill in the post What is Master the Art of Scheduling?

  • Meiosis and Gamete Formation

    Do you Know about Meiosis and Gamete Formation?

    Meiosis is a specialized type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants, and fungi. Errors in meiosis resulting in aneuploidy are the leading known cause of miscarriage and the most frequent genetic cause of developmental disabilities.

    In meiosis, DNA replication is followed by two rounds of cell division to produce four potential daughter cells, each with half the number of chromosomes as the original parent cell. The two meiotic divisions are known as Meiosis I and Meiosis II. Before meiosis begins, during S phase of the cell cycle, the DNA of each chromosome is replicated so that it consists of two identical sister chromatids, which remain held together through sister chromatid cohesion. This S-phase can be referred to as “premeiotic S-phase” or “meiotic S-phase.” Immediately following DNA replication, meiotic cells enter a prolonged G2-like stage known as meiotic prophase. During this time, homologous chromosomes pair with each other and undergo genetic recombination, a programmed process in which DNA is cut and then repaired, which allows them to exchange some of their genetic information. A subset of recombination events results in crossovers, which create physical links known as chiasmata (singular: chiasma, for the Greek letter Chi (X)) between the homologous chromosomes. In most organisms, these links are essential to direct each pair of homologous chromosomes to segregate away from each other during Meiosis I, resulting in two haploid cells that have half the number of chromosomes as the parent cell. During Meiosis II, the cohesion between sister chromatids is released and they segregate from one another, as during mitosis. In some cases all four of the meiotic products form gametes such as sperm, spores, or pollen. In female animals, three of the four meiotic products are typically eliminated by extrusion into polar bodies, and only one cell develops to produce an ovum.

    Because the number of chromosomes is halved during meiosis, gametes can fuse (i.e. fertilization) to form a diploid zygote that contains two copies of each chromosome, one from each parent. Thus, alternating cycles of meiosis and fertilization enable sexual reproduction, with successive generations maintaining the same number of chromosomes. For example, diploid human cells contain 23 pairs of chromosomes including 1 pair of sex chromosomes (46 total), half of maternal origin and half of paternal origin. Meiosis produces haploid gametes (ova or sperm) that contain one set of 23 chromosomes. When two gametes (an egg and a sperm) fuse, the resulting zygote is once again diploid, with the mother and father each contributing 23 chromosomes. This same pattern, but not the same number of chromosomes, occurs in all organisms that utilize meiosis.

    Meiosis

    Most plant and animal cells are diploid. The term diploid is derived from the Greek diplos, meaning “double” or “two”; the term implies that the cells of plants and animals have pairs of chromosomes. In human cells, for example, 46 chromosomes are organized in 23 pairs. Hence, human cells are diploid in that they have a pair of 23 individual chromosomes.

    During sexual reproduction, the sex cells of parent organisms unite with one another and form a fertilized egg cell (zygote). In this situation, each sex cell is a gamete. The gametes of human cells are haploid, from the Greek haplos, meaning “single.” This term implies that each gamete contains half of the 46 chromosomes—23 chromosomes in humans. When the human gametes unite with one another, the original diploid condition of 46 chromosomes is reestablished. Mitosis then brings about the development of the diploid cell into a multicellular organism.

    The process by which the chromosome number is halved during gamete formation is meiosis. In meiosis, a cell containing the diploid number of chromosomes is converted into four cells, each having the haploid number of chromosomes. In human cells undergoing meiosis, for instance, a cell containing 46 chromosomes yields four cells, each with 23 chromosomes.

    Meiosis occurs by a series of steps that resemble the steps of mitosis. Two major phases of meiosis occur: meiosis I and meiosis II. During meiosis I, a single cell divides into two. During meiosis II, those two cells each divide again. The same demarcating phases of mitosis take place in meiosis I and meiosis II—prophase, metaphase, anaphase, and telophase—but with some variations contained therein.

    As shown in Figure 1, first, the chromosomes of a cell are divided into two cells. The chromosomes of the two cells then separate and pass into four daughter cells. The parent cell is diploid, while each of the daughter cells has a single set of chromosomes and is haploid. Synapsis and crossing over occur in the prophase I stage.

    Meiosis and Gamete Formation Stages

    Figure 1  The process of meiosis, in which four haploid cells are formed.

    The members of each chromosome pair within a cell are called homologous chromosomes. Homologous chromosomes are similar but not identical. They may carry different versions of the same genetic information. For instance, one homologous chromosome may carry the information for blond hair while the other homologous chromosome may carry the information for black hair.

    Meiosis Phases

    As a cell prepares to enter meiosis, each of its chromosomes has duplicated in the synthesis stage (S) of the cell cycle, as in mitosis. Each chromosome thus consists of two sister chromatids.

    Meiosis I: At the beginning of meiosis, I, a human cell contains 46 chromosomes, or 92 chromatids (the same number as during mitosis). Meiosis I proceeds through the following phases:

    Prophase I: Prophase I is similar in some ways to prophase in mitosis. The chromatids shorten and thicken and become visible under a microscope. An important difference, however, is that a process called synapsis occurs. Synapsis is when the homologous chromosomes migrate toward one another and join to form a tetrad (the combination of four chromatids, two from each homologous chromosome). A second process called crossing over also takes place during prophase I. In this process, segments of DNA from one chromatid in the tetrad pass to another chromatid in the tetrad. These exchanges of chromosomal segments occur in a complex and poorly understood manner. They result in a genetically new chromatid. Crossing over is an important driving force of evolution. After crossing over has taken place, the homologous pair of chromosomes is genetically different.

    Metaphase I: In metaphase I of meiosis, the tetrads align on the equatorial plate (as in mitosis). The centromeres attach to spindle fibers, which extend from the poles of the cell. One centromere attaches per spindle fiber.

    Anaphase I: In anaphase I, the homologous chromosomes or tetrads separate. One homologous chromosome (consisting of two chromatids) moves to one side of the cell, while the other homologous chromosome (consisting of two chromatids) moves to the other side of the cell. The result is that 23 chromosomes (each consisting of two chromatids) move to one pole, and 23 chromosomes (each consisting of two chromatids) move to the other pole. Essentially, the chromosome number of the cell is halved once meiosis I is completed. For this reason, the process is a reduction-division.

    Telophase I: In telophase I of meiosis, the nucleus reorganizes, the chromosomes become chromatin, and the cell membrane begins to pinch inward. Cytokinesis occurs immediately following telophase I. This process occurs differently in plant and animal cells, just as in mitosis.

    Meiosis II: Meiosis II is the second major subdivision of meiosis. It occurs in essentially the same way as mitosis. In meiosis II, a cell contains a single set of chromosomes. Each chromosome, however, still has its duplicated sister chromatid attached. Meiosis II segregates the sister chromatids into separate cells. Meiosis II proceeds through the following phases:

    Prophase II: Prophase II is similar to the prophase of mitosis. The chromatin material condenses, and each chromosome contains two chromatids attached by the centromere. The 23 chromatid pairs, a total of 46 chromatids, then move to the equatorial plate.

    Metaphase II: In metaphase II of meiosis, the 23 chromatid pairs gather at the center of the cell prior to separation. This process is identical to metaphase in mitosis, except that this is occurring in a haploid versus a diploid cell.

    Anaphase II: During anaphase II of meiosis, the centromeres divide and sister chromatids separate, at which time they are referred to as non-replicated chromosomes. Spindle fibers move chromosomes to each pole. In all, 23 chromosomes move to each pole. The forces and attachments that operate in mitosis also operate in anaphase II.

    Telophase II: During telophase II, the chromosomes gather at the poles of the cells and become indistinct. Again, they form a mass of chromatin. The nuclear envelope develops, the nucleoli reappear, and the cells undergo cytokinesis.

    During meiosis II, each cell containing 46 chromatids yields two cells, each with 23 chromosomes. Originally, there were two cells that underwent meiosis II; therefore, the result of meiosis II is four cells, each with 23 chromosomes. Each of the four cells is haploid; that is, each cell contains a single set of chromosomes.

    The 23 chromosomes in the four cells from meiosis are not identical because crossing over has taken place in prophase I. The crossing over yields genetic variation so that each of the four resulting cells from meiosis differs from the other three. Thus, meiosis provides a mechanism for producing variations in the chromosomes. Also, it accounts for the formation of four haploid cells from a single diploid cell.

    Meiosis in Humans

    In humans, meiosis is the process by which sperm cells and egg cells are produced. In the male, meiosis takes place after puberty. Diploid cells within the testes undergo meiosis to produce haploid sperm cells with 23 chromosomes. A single diploid cell yields four haploid sperm cells through meiosis.

    In females, meiosis begins during the fetal stage when a series of diploid cells enter meiosis I. At the conclusion of meiosis, I, the process comes to a halt, and the cells gather in the ovaries. At puberty, meiosis resumes. One cell at the end of meiosis I enters meiosis II each month. The result of meiosis II is a single egg cell per cycle (the other meiotic cells disintegrate). Each egg cell contains 23 chromosomes and is haploid.

    The union of the egg cell and the sperm cell leads to the formation of a fertilized egg cell with 46 chromosomes, or 23 pairs. Fertilization restores the diploid number of chromosomes. The fertilized egg cell, a diploid, is a zygote. Further divisions of the zygote by mitosis eventually yield a complete human being.

    Gamete

    Gametes are the cells that fuse together during sexual reproduction to form a new organism. This lesson covers what these cells are, what they do, and the end result of when they meet.

    Definition of Gamete

    Gametes are the reproductive cells used during sexual reproduction to produce a new organism called a zygote. The gametes in males and females are different. The male gamete is called sperm. It is much smaller than the female gamete and very mobile. It has a long tail, flagellum, that allows it to move towards the female gamete. The female gamete is called an egg or ova. It is much larger than the sperm and is not made to move.

    Formation of Gametes

    Both the male and female gametes are formed during a process of cellular reproduction called meiosis. During meiosis, the DNA is only replicated or copied one time. However, the cells are divided into four separate cells. This means that the new gamete cells have only half of the number of chromosomes as the other cells. So, during meiosis DNA or chromosomes are copied, then split into two cells (with one full set of chromosomes each), then again split into two more cells, leaving only half of the pairs of chromosomes in each new cell.

    These new cells with only half of the chromosomes will mature into the gametes. The gametes are haploid cells because they have only one set of chromosomes. When they unite they will join their single sets of chromosomes to make a complete set, and then they will be considered diploid cells. In the female, the eggs or ova mature in the female’s ovaries. The sperm will mature in the male’s testes.