What Happens In Each Phase Of The Cell Cycle – The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells en route to cell division go through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produce two genetically identical cells. The cell cycle has two main phases: interphase and mitotic phase (Figure 6.3). During interphase, the cell grows and DNA replicates. During the mitotic phase, the replicated DNA and cytoplasmic contents are separated and the cell divides.
Figure 6.3 A cell goes through a series of phases in an orderly fashion. During interphase, G1 involves cell growth and protein synthesis, S phase involves DNA replication and centrosome replication, and G2 involves further growth and protein synthesis. Mitotic phase follows interphase. Mitosis is nuclear division during which duplicated chromosomes are separated and distributed into daughter nuclei. Normally, a cell will divide after mitosis in a process called cytokinesis, where the cytoplasm splits and two daughter cells are formed.
- 1 What Happens In Each Phase Of The Cell Cycle
- 2 Characterisation Of Cell Cycle Behaviour. (a). The Percentage Of Cells…
- 3 Solved Label This Figure With The Phases Of The Cell Cycle
What Happens In Each Phase Of The Cell Cycle
During interphase, the cell undergoes normal processes while preparing for cell division. For a cell to transition from interphase to mitotic phase, many internal and external conditions must be met. The three stages of interphase are called G
Solved Match Each Cell Cycle Phase To What Happens In That
Stage, the cell is quite active at the biochemical level. The cell accumulates the building blocks of chromosomal DNA and associated proteins, as well as accumulates enough energy reserves to carry out the task of replicating each chromosome in the nucleus.
During interphase, nuclear DNA remains in a semi-condensed chromatin configuration. In the S phase (the synthesis phase), DNA replication results in the formation of two identical copies of each chromosome—sister chromatids—that are firmly attached at the centromere region. At this stage, each chromosome is made up of two sister chromatids and is a duplicated chromosome. The centrosome duplicates during S phase. The two centrosomes will give rise to the mitotic spindle, the apparatus that organizes the movement of chromosomes during mitosis. A centrosome consists of a pair of rod-shaped centrioles at right angles to each other. Centrioles help organize cell division. Centrioles are not present in the centrosomes of many eukaryotic species, such as plants and most fungi.
Phase, or second gap, the cell replenishes its energy reserves and synthesizes the proteins necessary for chromosome manipulation. Certain cell organelles are duplicated and the cytoskeleton is disassembled to provide resources for the mitotic spindle. There may be additional cell growth during G
. The final preparations for the mitotic phase must be completed before the cell can enter the first stage of mitosis.
The Cell Cycle And Mitosis Review (article)
To form two daughter cells, the contents of the nucleus and cytoplasm must be separated. The mitotic phase is a multistep process during which the duplicated chromosomes line up, separate, and move to opposite poles of the cell, and then the cell divides into two new identical daughter cells. The first part of the mitotic phase, mitosis, consists of five stages that carry out nuclear division. The second part of the mitotic phase, called cytokinesis, is the physical separation of the cytoplasmic components into two daughter cells.
Mitosis is divided into a series of phases—prophase, prometaphase, metaphase, anaphase, and telophase—that lead to the division of the cell nucleus (Figure 6.4).
Figure 6.4 Animal cell mitosis is divided into five stages—prophase, prometaphase, metaphase, anaphase, and telophase—visualized here by fluorescence light microscopy. Mitosis is usually accompanied by cytokinesis, shown here with a transmission electron microscope. (credit “diagrams”: work modification by Mariana Ruiz Villareal; credit “mitosis micrographs”: work modification by Roy van Heesbeen; credit “cytokinesis micrograph”: work modification by Wadsworth Center, New York State Department of Health; donated to the Wikimedia Foundation; large-scale data by Matt Russell)
During prophase, the “first phase,” several events must occur to allow chromosomes to access the nucleus. The nuclear envelope begins to break down into small vesicles, and the Golgi apparatus and endoplasmic reticulum fragment and disperse to the periphery of the cell. The core disappears. The centrosomes begin to move to opposite poles of the cell. The microtubules that form the base of the mitotic spindle extend between the centrosomes, pushing them further apart as the microtubule fibers elongate. Sister chromatids begin to coil more tightly and become visible under a light microscope.
Fluctuation In Radioresponse Of Hela Cells During The Cell Cycle Evaluated Based On Micronucleus Frequency
During prometaphase, many processes that began in prophase continue to progress and culminate in the formation of a connection between the chromosomes and the cytoskeleton. The remnants of the nuclear envelope disappear. The mitotic spindle continues to develop as more microtubules are assembled and stretched along the former nuclear region. Chromosomes become more condensed and visually discrete. Each sister chromatid is attached to spindle-shaped microtubules at the centromere by a protein complex called a kinetochore.
During metaphase, all the chromosomes are arranged in a plane called the metaphase plate or equatorial plane, midway between the two poles of the cell. The sister chromatids are still tightly attached to each other. At this time, the chromosomes are maximally condensed.
During anaphase, sister chromatids in the equatorial plane separate at the centromere. Each chromatid, now called a chromosome, is rapidly pulled toward the centrosome to which its microtubule is attached. The cell becomes visibly elongated as non-kinetochore microtubules slide against each other at the metaphase plate, where they overlap.
During telophase, all the events that created the duplicated chromosomes for mitosis during the first three phases are reversed. The chromosomes reach the opposite poles and begin to decondense (disentangle). Mitotic spindles are broken down into monomers that will be used to assemble cytoskeletal components for each daughter cell. Nuclear envelopes form around the chromosomes.
Characterisation Of Cell Cycle Behaviour. (a). The Percentage Of Cells…
This page of movies illustrates various aspects of mitosis. Watch the movie titled “DIC Microscopy of Cell Division in a Newt Lung Cell” and identify the phases of mitosis.
Cytokinesis is the second part of the mitotic phase, during which cell division is completed by the physical separation of the cytoplasmic components into two daughter cells. Although the stages of mitosis are similar for most eukaryotes, the process of cytokinesis is quite different for eukaryotes that have cell walls, such as plant cells.
In cells such as animal cells that do not have cell walls, cytokinesis begins after the onset of anaphase. A contractile ring composed of actin filaments forms just inside the plasma membrane at the pre-metaphase plate. Actin filaments pull the equator of the cell inward, forming a cleft. This crack or “crack” is called a cleavage furrow. The furrow deepens as the actin ring contracts and eventually the membrane and the cell split in two (Figure 6.5).
In plant cells, the cleavage furrow is not possible because of the rigid cell walls surrounding the plasma membrane. A new cell wall must form between the daughter cells. During interphase, the Golgi apparatus accumulates enzymes, structural proteins, and glucose molecules before breaking up into vesicles and dispersing throughout the dividing cell. During telophase, these Golgi vesicles travel along microtubules to assemble at the metaphase plate. There the vesicles fuse from the center to the cell walls; this structure is called the cell plate. As more vesicles fuse, the cell plate enlarges until it fuses with the cell wall at the cell periphery. Enzymes use the glucose stored between the membrane layers to build a new cellulose cell wall. The Golgi membranes become the plasma membrane on both sides of the new cell wall (Figure 6.5).
Solved Label This Figure With The Phases Of The Cell Cycle
Figure 6.5 In part (a), a cleavage furrow forms at the previous metaphase plate in an animal cell. The plasma membrane is pulled by a ring of actin fibers contracting just inside the membrane. The cleavage furrow deepens until the cells are pinched in two. In part (b), Golgi vesicles fuse at the former metaphase plate in a plant cell. The vesicles fuse to form the cell plate. The cell plate grows from the center towards the cell walls. New cell walls are made from the contents of the vesicles.
Not all cells adhere to the classical model of the cell cycle, in which the newly formed daughter cell immediately enters interphase, closely followed by the mitotic phase. The cells in G
Phase are not actively preparing for separation. A cell is in a resting (inactive) stage after exiting the cell cycle. Some cells enter G
. Other cells that never or rarely divide, such as mature heart muscle and nerve cells, remain in G
S Phase (interphase) — Overview & Diagrams
Figure 6.6 Cells that are not actively preparing to divide enter an alternate phase called G0. In some cases, this is a temporary state until it is triggered to enter G1. In other cases, the cell will remain in G0 permanently.
The length of the cell cycle is highly variable even within the cells of an individual organism. In humans, the frequency of cell turnover varies from a few hours in early embryonic development to an average of two to five days for epithelial cells, or to an entire human lifetime spent in G
From specialized cells such as cortical neurons or cardiac
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