Prophase is the first step of mitosis, during which chromosomes condense and the nuclear envelope dissolves. Metaphase follows prophase. During metaphase, the chromosomes align in the center of the cell at the equatorial plate and the spindle fibers attach to the centromeres of the chromosomes.
Anaphase involves the retraction of the spindle fibers and the separation fo sister chromatids. The nuclear envelope begins to develop and the cell prepares for the final division during telophase.
Cytokinesis is not generally included in the phases of mitosis, and refers to the final separation of the cell cytoplasm into two identical daughter cells.
Interphase refers to the portion of the cell cycle during which the cell is not dividing, and includes the G1, S, and G2 phases. The mitosis M phase of the cell cycle has four sequential stages: prophase, metaphase, anaphase, and telophase.
In the first stage, prophase, each chromosome becomes condensed and more visible, and there is the breakdown of the nuclear membrane and appearance of spindle fibers. In the next phase, metaphase, the chromosomes line up along the metaphasic plate. The spindle fibers are completely formed and are attached to each sister chromatid of the chromosomes. Next, during anaphase, the centromeres holding the sister chromatids together are divided and the sister chromatids are pulled apart by the spindle fibers to opposite poles of the diving cell.
During the last phase of mitosis, telophase, the two sets of chromosomes reach the poles of the cell. This is followed by the reformation of the nuclear envelope, uncoiling of the DNA, and disappearance of the spindle fibers.
Centromeres are the structures at the center of each chromosome that hold the sister chomatids together. The division of the centromeres occurs during anaphase. This allows for the separation of each sister chromatid into its respective daughter cell.
Mitosis has four sequential stages: prophase, metaphase, anaphase, and telophase. In prophase, each chromosome becomes condensed and more visible, and there is the breakdown of the nuclear membrane and appearance of spindle fibers.
During the last phase of mitosis, telophase, the two sets of chromosomes reach the opposite poles of the cell. After the M phase is the separation of the cytoplasm, known as cytokinesis, which results in two distinct daughter cells.
In the next phase, metaphase, the chromosomes line up along the metaphase plate. In which phase of mitosis does a cell utilize a specific control mechanism to verify its readiness for DNA synthesis? The G1 phase is the first phase within interphase. It can more easily be remembered as the "first growth" phase. During this period the cell increases its supply of proteins while also increasing the number of organelles such as ribosomes and mitochondria in addition to growing in size.
This stage is critical toward making sure that the cell has appropriate resources for DNA synthesis. After G1, S phase proceeds. In which phase has the cell left the cell cycle and has stopped dividing, in other words, which of the following is the resting phase? G0 phase is a post-mitotic phase. It may be a permanent as often is the case for neurons or semi-permanent for some liver, kidney, and stomach cells phase.
Epithelial cells do not enter G0, allowing these cells to continue to divide throughout an organisms life.
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Correct answer: Anaphase. The membranous organelles such as the Golgi apparatus and endoplasmic reticulum fragment and disperse toward the periphery of the cell.
The nucleolus disappears and the centrosomes begin to move to opposite poles of the cell. Microtubules that will eventually form the mitotic spindle extend between the centrosomes, pushing them farther apart as the microtubule fibers lengthen. The sister chromatids begin to coil more tightly with the aid of condensin proteins and become visible under a light microscope. The remnants of the nuclear envelope fragment.
The mitotic spindle continues to develop as more microtubules assemble and stretch across the length of the former nuclear area. Chromosomes become more condensed and discrete.
Each sister chromatid develops a protein structure called a kinetochore in the centromeric region. The proteins of the kinetochore attract and bind mitotic spindle microtubules. Kinetochore and Mitotic Spindle : During prometaphase, mitotic spindle microtubules from opposite poles attach to each sister chromatid at the kinetochore. In anaphase, the connection between the sister chromatids breaks down and the microtubules pull the chromosomes toward opposite poles.
The sister chromatids are still tightly attached to each other by cohesin proteins. At this time, the chromosomes are maximally condensed. Each chromatid, now called a chromosome, is pulled rapidly toward the centrosome to which its microtubule is attached. The cell becomes visibly elongated oval shaped as the polar microtubules slide against each other at the metaphase plate where they overlap. The mitotic spindles are depolymerized into tubulin monomers that will be used to assemble cytoskeletal components for each daughter cell.
Nuclear envelopes form around the chromosomes and nucleosomes appear within the nuclear area. Division is not complete until the cell components have been apportioned and completely separated into the 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, which lack cell walls, cytokinesis follows the onset of anaphase.
A contractile ring composed of actin filaments forms just inside the plasma membrane at the former metaphase plate. The actin filaments pull the equator of the cell inward, forming a fissure. The furrow deepens as the actin ring contracts; eventually the membrane is cleaved in two. Cytokinesis : During cytokinesis in animal cells, a ring of actin filaments forms at the metaphase plate. The ring contracts, forming a cleavage furrow, which divides the cell in two.
In plant cells, Golgi vesicles coalesce at the former metaphase plate, forming a phragmoplast. A cell plate formed by the fusion of the vesicles of the phragmoplast grows from the center toward the cell walls and the membranes of the vesicles fuse to form a plasma membrane that divides the cell in two.
In plant cells, a new cell wall must form between the daughter cells. During interphase, the Golgi apparatus accumulates enzymes, structural proteins, and glucose molecules prior to breaking into vesicles and dispersing throughout the dividing cell. During telophase, these Golgi vesicles are transported on microtubules to form a phragmoplast a vesicular structure at the metaphase plate. There, the vesicles fuse and coalesce from the center toward the cell walls; this structure is called a cell plate.
Kinetochore microtubules attach the chromosomes to the spindle pole; interpolar microtubules extend from the spindle pole across the equator, almost to the opposite spindle pole; and astral microtubules extend from the spindle pole to the cell membrane. Metaphase leads to anaphase , during which each chromosome's sister chromatids separate and move to opposite poles of the cell.
Enzymatic breakdown of cohesin — which linked the sister chromatids together during prophase — causes this separation to occur. Upon separation, every chromatid becomes an independent chromosome. Meanwhile, changes in microtubule length provide the mechanism for chromosome movement. More specifically, in the first part of anaphase — sometimes called anaphase A — the kinetochore microtubules shorten and draw the chromosomes toward the spindle poles. Then, in the second part of anaphase — sometimes called anaphase B — the astral microtubules that are anchored to the cell membrane pull the poles further apart and the interpolar microtubules slide past each other, exerting additional pull on the chromosomes Figure 2.
Figure 2: Types of microtubules involved in mitosis During mitosis, several types of microtubules are active. The motor proteins associated with the interpolar microtubules drive the assembly of the spindle. Note the other types of microtubules involved in anchoring the spindle pole and pulling apart the sister chromatids. Figure Detail. Cytokinesis is the physical process that finally splits the parent cell into two identical daughter cells. During cytokinesis, the cell membrane pinches in at the cell equator, forming a cleft called the cleavage furrow.
The position of the furrow depends on the position of the astral and interpolar microtubules during anaphase. The cleavage furrow forms because of the action of a contractile ring of overlapping actin and myosin filaments. As the actin and myosin filaments move past each other, the contractile ring becomes smaller, akin to pulling a drawstring at the top of a purse.
When the ring reaches its smallest point, the cleavage furrow completely bisects the cell at its center, resulting in two separate daughter cells of equal size Figure 3. Figure 3: Mitosis: Overview of major phases The major stages of mitosis are prophase top row , metaphase and anaphase middle row , and telophase bottom row.
This page appears in the following eBook. Aa Aa Aa. What Are the Phases of Mitosis? Figure 1: Drawing of chromosomes during mitosis by Walther Flemming, circa What Happens during Prophase? What Happens during Prometaphase? Each microtubule is highly dynamic, growing outward from the centrosome and collapsing backward as it tries to locate a chromosome.
Eventually, the microtubules find their targets and connect to each chromosome at its kinetochore , a complex of proteins positioned at the centromere. The actual number of microtubules that attach to a kinetochore varies between species, but at least one microtubule from each pole attaches to the kinetochore of each chromosome.
A tug-of-war then ensues as the chromosomes move back and forth toward the two poles. What Happens during Metaphase and Anaphase? Figure 2: Types of microtubules involved in mitosis. During mitosis, several types of microtubules are active.
What Happens during Telophase? During telophase , the chromosomes arrive at the cell poles, the mitotic spindle disassembles, and the vesicles that contain fragments of the original nuclear membrane assemble around the two sets of chromosomes.
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