Biological Sciences
Mitosis
Mitosis is a process of cell division in which a single cell divides to produce two identical daughter cells. It consists of several stages, including prophase, metaphase, anaphase, and telophase, each characterized by specific events such as chromosome condensation, alignment, separation, and reformation of the nuclear envelope. Mitosis plays a crucial role in growth, repair, and asexual reproduction in organisms.
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5 Key excerpts on "Mitosis"
eBook - ePub- Patrick Arbuthnot, Silke Arndt, Sahle Asfaha, Jacqueline Brown, Alexio Capovilla, Arnold Christianson, Gerrit Coetzee, Theresa Coetzer, Leandra Cronjé, Nigel Crowther, Chrisna Durandt, Adriano Duse, Lindsay Earlam, Debbie Glencross, Nerine Gregersen, Kate Hammond, Tabitha Haw, Nicole Holland, Penny, Barry Mendelow, Michèle Ramsay, Nanthakumarn Chetty, Wendy Stevens(Authors)
- 2008(Publication Date)
- Wits University Press(Publisher)
Mitosis is the process of cell division in which the original number of chromosomes in a parent cell is maintained and two daughter cells are produced from the division of one parent cell. A diploid cell (2n) divides under Mitosis to produce two diploid daughter cells. Mitosis occurs in most body tissues that are renewed on a continual basis.During interphase, the DNA of all chromosomes replicates. As a result, each chromosome comprises two sister chromatids. The sister chromatids are joined at the centromere, and remain joined throughout cell division until anaphase. Mitosis comprises the following five steps: prophase, prometaphase, metaphase, anaphase and telophase(Figure 3 ).Fig. 3:Mitosis.Prophase. Each chromosome starts to condense along its length. Spindle formation begins. The centrioles form two poles at opposite sides of the cell. They are connected by microtubules. The nucleolus disappears.Prometaphase. Microtubules from the spindle are attached to the kinetochore of each sister chromatid of a chromosome. Each kinetochore on one chromosome is orientated to opposite poles of the spindle. The nuclear membrane is broken down.Metaphase. The chromosomes are now at their most condensed and each chromosome lines up at the centre of the spindle, along the equator (note: homologous chromosomes are not paired).Anaphase. The centromere of each chromosome divides longitudinally. The microtubule fibres contract and the sister chromatids of each chromosome are pulled apart towards opposite poles of the spindle.Telophase. The new chromosomes are now at the poles and the cell wall begins invagination. Microtubules start to disappear. The spindle mid-section begins to clear. Vesicles congregate at the spindle midline to assist in the assembly of a new cell wall. The nuclear envelope reappears. Each of the two resulting cells should contain the whole diploid set of cellular chromosomes.Meiosis
Meiosis is a process of cell division necessary for the production of gamete cells, and it therefore occurs only in the gonads. A single diploid cell (2n) that undergoes meiosis has four resulting daughter cells, each containing a haploid set (n) of chromosomes. In oogenesis, one of the daughter cells results in an ovum, while the other three are polar bodies. One oogonium forms a primary oocyte. In the first meiotic cell division, this primary oocyte divides into a secondary oocyte and polar body. The secondary oocyte undergoes the second stage of meiosis and forms an oocyte and a polar body. During spermatogenesis, each primary spermatocyte divides into four mature sperm cells. The cell division process is divided into two separate division cycles: meiosis I and meiosis II(Figure 4
eBook - ePub- Thomas D. Pollard, William C. Earnshaw, Jennifer Lippincott-Schwartz, Graham Johnson(Authors)
- 2016(Publication Date)
- Elsevier(Publisher)
Mitosis has been studied since the 1800s, but technical advances have considerably advanced our understanding of how it is accomplished at the molecular level. Division requires wholesale reorganization of cellular structures, including chromosome condensation and the assembly of the mitotic spindle. In many cells, the nuclear envelope breaks down. Once the chromosomes are all attached to the microtubules of the mitotic spindle (yet another important checkpoint here), they are separated equally and form two daughter nuclei. Finally, cytokinesis separates the two daughter cells. Chapter 45 considers meiosis, a specialized form of division that produces the gametes required for sexual reproduction. In this division, DNA recombination is key to segregation of the chromosomes. A number of arcane terms are used to describe the specialized structures and processes involved. The chapter then explains how problems with meiosis can lead to genetic diseases and how studies of chromosome segregation in yeast led to an understanding of why birth defects become more prevalent as human mothers age. Chapter 46 closes the book with a discussion of what happens when cells commit suicide by apoptosis, necroptosis, and autophagy. This is not, strictly speaking, a cell-cycle event but instead represents several alternative pathways, each with its own machinery and signaling systems. Apoptosis sometimes results when it all “runs off the rails” and cells receive insults from which they cannot recover. But cell death is not always bad: apoptosis is an essential part of development of metazoan organisms, homeostasis of their organs and tissues, and can be a last-ditch defense against viral infection. Malfunctions of apoptotic pathways can lead to cancer. The concepts that are discussed in this section of the book build on the ideas in earlier sections. Cells are wonderfully complex systems whose behavior is driven by the laws of chemistry and physics
eBook - ePub- Rene Fester Kratz(Author)
- 2017(Publication Date)
- For Dummies(Publisher)
centromere.- G2 phase: During this phase, the cell is packing its bags and getting ready to hit the road for cell division by making the cytoskeletal proteins it needs to move the chromosomes around. When you look at cells that are dividing, the cytoskeletal proteins look like thin threads, hence their name — spindle fibers. A network of spindle fibers spreads throughout the cell during Mitosis to form the mitotic spindle, which is represented by the thin curving lines drawn in the cells in Figure 6-2 . The mitotic spindle organizes and sorts the chromosomes during Mitosis.
Mitosis: One for you, and one for you
After interphase is over (see the preceding section), cells that are going to divide to create an exact replica of a parent cell enter Mitosis. During Mitosis, the cell makes final preparations for its impending split. Processes during Mitosis ensure that genetic material is distributed equally so each new daughter cell receives identical information (eukaryotic cells are model parents intent on avoiding bickering between their daughter cells).The process of Mitosis occurs in four phases, with the fourth phase initiating a final process called cytokinesis. We outline everything for you in the following sections.Examining the four phases of Mitosis
Although the cell cycle is a continuous process, with one stage flowing into another, scientists divide the events of Mitosis into four phases based on the major events in each stage.The four phases of Mitosis are prophase, metaphase, anaphase, and telophase. You can remember these by remembering this phrase: “The cat Peed on the MAT.’ PMAT represents the four phases in order.The main events in the four phases of Mitosis are- Prophase: The chromosomes of the cell get ready to be moved around by coiling themselves up into tight little packages. (During interphase, the DNA is spread throughout the nucleus of the cell in long thin strands that would be pretty hard to sort out.) As the chromosomes coil up, or condense,
eBook - ePub- Rene Fester Kratz, Donna Rae Siegfried(Authors)
- 2019(Publication Date)
- For Dummies(Publisher)
centromere.- G2 phase: During this phase, the cell is packing its bags and getting ready to hit the road for cell division by making the cytoskeletal proteins it needs to move the chromosomes around. When you look at cells that are dividing, the cytoskeletal proteins look like thin threads, hence their name — spindle fibers. A network of spindle fibers spreads throughout the cell during Mitosis to form the mitotic spindle, which is represented by the thin curving lines drawn in the cells in Figure 5-2 . The mitotic spindle organizes and sorts the chromosomes during Mitosis.
Mitosis: One for you, and one for you
After interphase is over, cells that are going to divide to create an exact replica of a parent cell enter Mitosis, or the M phase of the cell cycle. During Mitosis, the cell makes final preparations for its impending split. Processes during Mitosis ensure that genetic material is distributed equally so each new daughter cell receives identical information. (Eukaryotic cells are model parents intent on avoiding bickering between their daughter cells.)The process of Mitosis occurs in four phases, with the fourth phase initiating a final process called cytokinesis. We outline everything for you in the following sections.The four phases of Mitosis
Although the cell cycle is a continuous process, with one stage flowing into another, scientists divide the events of Mitosis into four phases based on the major events in each stage. The four phases of Mitosis are- Prophase: The chromosomes of the cell get ready to be moved around by coiling themselves up into tight little packages. (During interphase, the DNA is spread throughout the nucleus of the cell in long thin strands that would be pretty hard to sort out.) As the chromosomes coil up, or condense, they become visible to the eye when viewed through a microscope. During prophase:
- The chromosomes coil up and become visible.
- The nuclear membrane breaks down.
- The mitotic spindle forms and attaches to the chromosomes.
- The nucleoli break down and become invisible.
eBook - ePubHuman Genes and Genomes
Science, Health, Society
- Leon E. Rosenberg, Diane Drobnis Rosenberg(Authors)
- 2012(Publication Date)
- Academic Press(Publisher)
FIGURE 4.4 Mitotic cell division. Two chromosome pairs are shown. Note that each homologous chromosome has already been duplicated before Mitosis starts and consists of two sister chromatids. In this figure, red designates maternally inherited chromosomes and green designates paternally inherited chromosomes. The details of the various phases and their relationship to the cell cycle are discussed in the text. The net result: two daughter cells identical to the parent cell.Meiotic Division
In contrast to mitotic division, which occurs in all body cells, meiotic division , or meiosis , is a type of cell division found only in male and female germ cells . Rather than producing two identical, diploid daughter cells from one round of cell division, as Mitosis does, meiosis consists of two rounds of cell division (called “meiosis I ” and “meiosis II ”), ultimately yielding gametes each of which is haploid rather than diploid. Upon completion of meiosis I (also called “reduction division ”), each daughter cell contains half of the diploid number of chromosomes (thus is called “haploid ”). In meiosis II, each haploid cell divides into two more haploid cells. In essence, then, meiosis constitutes the means by which one diploid cell divides into four haploid gametes (Figure 4.5 ). Critical for the organism, genetic diversity is a product of meiosis. Such diversity reflects two properties, each occurring during meiosis I: random segregation of chromosomes, and recombination between members of a chromosome pair. What follows are more detailed descriptions of meiosis I and meiosis II.FIGURE 4.5
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