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MEIOSISPHASE
holt biology The cell cycle ]
chapter 12 the cell cycle
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Recommended: MEIOSISPHASE
Michael Cooney
Introduction
The cell cycle is the synchronous process by which existing cells give rise to new cells. This process can be broadly divided into two stages: interphase and mitosis. During interphase, cells increase in size, replicate their chromosomes to form sister chromatids, and increase their rates of protein synthesis. During mitosis, sister chromatids are separated and transported to opposite cell poles, followed by cell division (cytokinesis). Recent investigations have revealed much information about the morphological changes that occur in mitotic cells. These morphological changes occur in a precise order and include, in chronological order, condensation of chromosomes, changes in microtubule assembly patterns, nuclear envelope breakdown, chromosome alignment at the center of the cell, chromosome separation to opposite cell poles, and nuclear envelope reassembly prior to cytokinesis. Similar morphological changes have been observed during meiosis, indicating that the processes driving DNA distribution in somatic cells and gametes is similar (Baserga, 1968).
Though these morphological changes have been known for some time, very little is known about the mechanisms underlying them. The processes that govern cell cycle regulation are of great interest to researchers, as aberrations like improper chromosome segregation and nonfunctional microtubule assembly can result in apoptosis or, if the cell doesn’t undergo apoptosis, cancer. Most evidence surrounding cell cycle regulation comes from studies on embryonic development of amphibians. Amphibian eggs contain many of the proteins required to carry out mitosis, but can only enter mitosis after fertilization. In addition to these proteins, the eggs contain a v...
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...ty of cyclin variants with mutations in the 13-90 amino acid region to induce the transition to interphase could specifically identify the amino acids that are required for cyclin degradation, perhaps providing a clue as to the responsible mechanism.
References
1. “Biochemistry of the cell cycle: A review”, Baserga. Cell Proliferat.1(2): 167-191.
2. “The effect of protein synthesis inhibition on the entry of messenger RNA into the cytoplasm of sea urchin embryos”, Hogan and Gross. J. Cell Biol. 49(3):692-701.
3. “Accumulation of histone repeat transcripts in the sea urchin egg pronucleus”, Venezsky et al. Cell. 24(2):385-391.
4. “Role of hormones in oocyte maturation”, Schuetz. Biol. Reprod. 10(2):150-178.
5. “Cell cycle dynamics of an M-phase-specific cytoplasmic factor in Xenopus laevis oocytes and eggs”, Gerhart et al. J Cell Biol. 98(4): 1247-1255.
The fungus Sordaria fimicola is commonly used to study the different processes of cell cycles such as the assortment of genes and the crossing over during meiosis. Considering the importance of genetics in the world today, this experiment is crucially valuable in helping the students gain knowledge in the different processes of cell cycle and learning how to attempt similar experiments on their own in the future. Sordaria fimicola requires “both mitotic and meiotic nuclear divisions to manufacture eight haploid ascospores” (Helm, 1998). This fungus “spend most of its life in haploid condition” (Glase, 1995). When the haploid nuclei fuse together in the cells, they beco...
Cell cycle events portray some differences between different living things. In all the three living things, their cells divide, a process referred to as mitosis. The mitosis stage differs and it encompasses four phases. During development, the cell cycle functions endlessly with newly created daughter cells directly embarking on their path to mitosis. Bacteria cells separate forming two cells after every thirty minutes under favorable conditions. However, the eukaryotic cells take quite longer compared to bacteria cells to develop and divide. Nevertheless, in both animals and plants, cell cycle is usually highly regulated to prevent imbalanced and excessive growth. Both animals and plants are known as eukaryotes meaning that their DNA exists inside their cells’ nuclei. Therefore, their cells as well as mitotic processes are similar in various ways (Eckardt, 2012).
Meiosis, also called reduction division, is a distinct type of cell division that is essential for sexual reproduction to occur. It is one in which two successive divisions of diploid cell occur thereby producing four genetically different haploid daughter cells, also called gametes, each with half the number of chromosomes and thus, half the total amount of genetic material as compared to the amount before meiosis began. Interphase precedes meiosis and thus, paves the way for meiosis to eventuate as the cell’s DNA replicates in the S phase yielding corresponding, identical chromosomes. Interphase sparks the marvelous process of meiosis that allows variation to transpire within the organisms it occurs, hence, giving rise to millions of organisms with unique aspects unlike any other on Earth. Because meiosis is a form of sexual reproduction itself, it is the means through which gametes are produced, each with a reduced number of chromosomes, so that when two gametes fuse during fertilization, not only do they form a diploid zygote with 46 chromosomes, but also have manifested differing features due to the rearrangement (crossing-over) of chromosomes.
Mitosis describes the reproduction of somatic cells, and Meiosis describes the reproduction of sex cells. We have discussed that Interphase, although not actually a part of Mitosis, is the longest phase and that Prophase involves the dissolution of the nuclear envelope, the condensing of chromatin into chromosomes, and the formation of mitotic spindles that attach to the centromeres of the chromosome pairs. After Prophase comes Metaphase where the chromosomes line up in the center of the cell at the metaphase plate. Next, Anaphase occurs where sister chromatids separate to become two separate chromosomes that then move to opposite poles of the cell. This results in the cell’s shape becoming elongated and the chromosome pairs splitting apart. Lastly, Telophase follows Anaphase and nuclei form around the two sets of chromosomes that then become less condensed. In Telophase, the microtubules break down too, and this phase is overlapped at the end of Mitosis with Cytokinesis that involves the final splitting of the two
Meiosis is specialized cellular division of sex cells. This type of cellular division occurs in single and multi-cellular organisms that undergo sexual reproduction. This process is split into two cycles: Meiosis I and Meiosis II. Prior to the start of meiosis, interphase occurs. Although interphase is not a stage of meiosis it is a vital preparatory step. It allows cellular growth, DNA replication and prepares for cellular division. Each cycle of meiosis is broken down into four stages for a total of eight stages. Meiosis I is composed of prophase I, metaphase I, anaphase I, and telophase I. Meiosis II is a repeat of each phase of meiosis I. Once meiosis is complete, the result will be four haploid daughter cells meaning that each daughter
During interphase, cell growth, DNA replication, separation of centrioles and protein synthesis takes place. This phase is acknowledged to being the most extensive period of the cell cycle thus signifying the stage in which the cell devotes th...
This result is not surprising because the cell needs time to replicate DNA as well as the other cell organelles. Prophase had the second most number of cells. In prophase, the cell has to turn the loose chromatin into sister chromatids. This phase is also when the nuclear membrane starts to dissolve and when the centrioles move to opposite parts of the cell. Metaphase is when the spindle fibers attach onto the centromeres and the chromatids line up in the center. This part of mitosis was rather fast and this may be because the centroids already started moving to either end of the cell in prophase. In anaphase, the daughter chromosomes are pulled to either end of the cell. This phase ends when the daughter chromosomes are at both ends. There is no big change in this phase other than the fact the sister chromatids separated and moved to either end of the cell. The last phase of mitosis telophase is when the cell actually begins to divide. However, the onion root tip cell is a plant cell so it develops a cell wall in-between the two daughter
Mitosis has 4 identifiable stages: prophase, metaphase, anaphase, and telophase/cytokinesis. Prophase is the first stage of mitotic cellular division in which the centrioles separate and move to opposite ends of the nucleus. Proceeding is prometaphase, whereas described above, is when microtubules attach to the chromosomes to prepare them for the next phase: Metaphase. Metaphase is the third step of mitosis where the chromosomes align along the metaphase plate to prepare for division. To form the two daughter cells, anaphase, the next stage, separates the chromosomes and they move to opposite ends of the cell. Lastly, telophase/cytokinesis occurs in which the nuclear envelope reforms, the cellular membrane (and cell wall in plant cells) is cleaved and rebuilt. From that process two identical daughter cells are
3. Observe the prepared microscope slide of the fish blastodisc mitosis first at 100X, then 400X. Look for cells in mitosis and classify the stages. Compare and record similarities and contrast differences between the animal and plant cell mitosis.
In Meiosis I, Prophase I is the starting step in which the parent cell’s chromosomes condense and the nuclear membrane begins to disintegrate. Additionally, two pairs of centrioles are created and move to opposite sides. Crossing over occurs in this step as well. Crossing over is the act of homologous chromosomes trading parts of their chromosomes. This process is to allow genetic diversity within offspring and occurs randomly. The replicated chromosomes in this stage are called tetrads, which are cells with two chromosomes and consequently four sister chromatids. Sister chromatids are two chromatids which, together, make up a chromosome. Following Prophase I is Metaphase I, in which the
Mitosis is a part of the cell cycle process because chromosomes in a cell nucleus are separated into
The two new pair of centrioles arise from the proximal end of each of the older centrioles, and elongate to reach the same length as the parent centrioles. The original mother and daughter centrioles completely separate from each other, along with their new daughter centrioles to form two new centrosomes. Each of the two resulting centrosomes thus contain one centriol from the older generation and one newly formed centriole (semiconservative replication). The PCM also gets divided between the two new centrosomes. The sequence of steps of the centrosome duplicaiton cycle shows variations in some cells. For example, in Drosophila melanogaster embryo, the PCM divides before the new daughter centrioles are
Campbell, N. A. & J. B. Reece, 8th eds. (2008). Biology. San Francisco: Pearson Benjamin Cummings.
nuclei was then inactivated and substituted with dead nuclei from the extinct frog. Some eggs started to grow and divide to early embryo stage (a tiny ball of m...
There are certain things that must happen first before the cell can actually split. There is a six step process required during Mitosis. The first five steps of mitosis are called prophase, prometaphase, metaphase, anaphase, and telophase. This is where all the training and preparation is done for cell division. The sixth step is Cytokinesis, and that is when the cell literally splits into two. Like I said, there are certain things in order to happen before it can enter the M phase. first, it must meet the requirements of the certain size and environment. Since in the S phase the cell duplicated it’s amount of chromosomes it be represented as 2N, where N equals the number of chromosomes in the cell. Cells about to enter M phase, which have passed through S phase and replicated their DNA, have 4N chromosomes. Because of this they are now allowed to enter within the M phase to prophase. Here is where the cell thickens up its chromosomes and begin to sprout microtubules from clone centrosomes. Microtubules tub-like are protein filaments and where the chromosomes migrate but are still within the nuclear envelope in the nucleus. There are centromeres, that are inside the chromosomes and during the later process of this phase, specialized microtubules called kinetochores, assemble on the centromere then later attach to these sites. They act like magnets and go