what happens to the mitotic spindle during mitosis
Mitosis is the process in which a eukaryotic prison cell nucleus splits in 2, followed past division of the parent prison cell into ii daughter cells. The word "mitosis" means "threads," and it refers to the threadlike appearance of chromosomes as the jail cell prepares to divide. Early microscopists were the first to discover these structures, and they also noted the advent of a specialized network of microtubules during mitosis. These tubules, collectively known as the spindle, extend from structures chosen centrosomes — with one centrosome located at each of the opposite ends, or poles, of a prison cell. As mitosis progresses, the microtubules attach to the chromosomes, which have already duplicated their Deoxyribonucleic acid and aligned across the center of the cell. The spindle tubules so shorten and motility toward the poles of the cell. Equally they move, they pull the one copy of each chromosome with them to reverse poles of the cell. This process ensures that each daughter prison cell volition contain one exact copy of the parent cell Deoxyribonucleic acid.
What Are the Phases of Mitosis?
Mitosis consists of 5 morphologically distinct phases: prophase, prometaphase, metaphase, anaphase, and telophase. Each stage involves characteristic steps in the process of chromosome alignment and separation. Once mitosis is complete, the entire prison cell divides in two by fashion of the process called cytokinesis (Figure 1).
Figure 1: Drawing of chromosomes during mitosis past Walther Flemming, circa 1880
This illustration is one of more than i hundred drawings from Flemming'southward \"Cell Substance, Nucleus, and Cell Partitioning.\" Flemming repeatedly observed the dissimilar forms of chromosomes leading upward to and during cytokinesis, the ultimate division of ane jail cell into 2 during the last phase of mitosis.
© 2001 Nature Publishing Group Paweletz, N. Walther Flemming: pioneer of mitosis research. Nature Reviews Molecular Prison cell Biological science two, 72 (2001). All rights reserved. 
What Happens during Prophase?
Prophase is the first stage in mitosis, occurring later on the conclusion of the G2 portion of interphase. During prophase, the parent cell chromosomes — which were duplicated during S phase — condense and get thousands of times more than compact than they were during interphase. Because each duplicated chromosome consists of two identical sis chromatids joined at a point chosen the centromere, these structures at present announced equally X-shaped bodies when viewed nether a microscope. Several DNA binding proteins catalyze the condensation process, including cohesin and condensin. Cohesin forms rings that agree the sister chromatids together, whereas condensin forms rings that gyre the chromosomes into highly compact forms.
The mitotic spindle also begins to develop during prophase. As the cell's two centrosomes move toward opposite poles, microtubules gradually assemble betwixt them, forming the network that will later pull the duplicated chromosomes apart.
What Happens during Prometaphase?
When prophase is complete, the cell enters prometaphase — the second phase of mitosis. During prometaphase, phosphorylation of nuclear lamins by G-CDK causes the nuclear membrane to break down into numerous small vesicles. As a result, the spindle microtubules at present have direct access to the genetic material of the cell.
Each microtubule is highly dynamic, growing outward from the centrosome and collapsing astern every bit it tries to locate a chromosome. Somewhen, 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 betwixt species, just at least ane microtubule from each pole attaches to the kinetochore of each chromosome. A tug-of-war then ensues every bit the chromosomes move back and forth toward the ii poles.
What Happens during Metaphase and Anaphase?
As prometaphase ends and metaphase begins, the chromosomes align along the prison cell equator. Every chromosome has at least 2 microtubules extending from its kinetochore — with at least ane microtubule connected to each pole. At this point, the tension within the jail cell becomes counterbalanced, and the chromosomes no longer move dorsum and forth. In addition, the spindle is now complete, and 3 groups of spindle microtubules are apparent. Kinetochore microtubules adhere the chromosomes to the spindle pole; interpolar microtubules extend from the spindle pole beyond 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'due south sister chromatids separate and motion to reverse poles of the jail cell. Enzymatic breakup of cohesin — which linked the sister chromatids together during prophase — causes this separation to occur. Upon separation, every chromatid becomes an contained chromosome. Meanwhile, changes in microtubule length provide the machinery for chromosome movement. More specifically, in the showtime part of anaphase — sometimes called anaphase A — the kinetochore microtubules shorten and describe the chromosomes toward the spindle poles. Then, in the second part of anaphase — sometimes chosen anaphase B — the astral microtubules that are anchored to the prison 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.
What Happens during Telophase?
During telophase, the chromosomes arrive at the jail cell poles, the mitotic spindle disassembles, and the vesicles that comprise fragments of the original nuclear membrane assemble around the two sets of chromosomes. Phosphatases then dephosphorylate the lamins at each cease of the cell. This dephosphorylation results in the germination of a new nuclear membrane around each grouping of chromosomes.
When Exercise Cells Really Split up?
Cytokinesis is the concrete process that finally splits the parent prison cell into two identical daughter cells. During cytokinesis, the cell membrane pinches in at the prison cell equator, forming a scissure 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 activity of a contractile ring of overlapping actin and myosin filaments. Equally the actin and myosin filaments motion past each other, the contractile band becomes smaller, akin to pulling a drawstring at the meridian of a handbag. When the ring reaches its smallest point, the cleavage furrow completely bisects the cell at its center, resulting in two divide girl cells of equal size (Figure 3).
Figure 3: Mitosis: Overview of major phases
The major stages of mitosis are prophase (peak row), metaphase and anaphase (center row), and telophase (bottom row).
Decision
Mitosis is the process of nuclear division, which occurs just prior to prison cell division, or cytokinesis. During this multistep procedure, cell chromosomes condense and the spindle assembles. The duplicated chromosomes and then attach to the spindle, marshal at the jail cell equator, and motion apart as the spindle microtubules retreat toward opposite poles of the cell. Each set of chromosomes is and then surrounded by a nuclear membrane, and the parent cell splits into two complete daughter cells.
Source: https://www.nature.com/scitable/topicpage/mitosis-14046258/#:~:text=As%20mitosis%20progresses%2C%20the%20microtubules,opposite%20poles%20of%20the%20cell.
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