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Cell Cycle M Phase – Overview, Mitosis, Phases, Examples

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  • Last Updated : 05 Aug, 2022
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The cell cycle (Howard and Pelc, 1953) is a genetically managed group of changes that occur in a newly formed cell by which it supplicates in the contents, Undergoes, division, and growth to form two daughters. It consists of two states or periods, a long growth that is nondividing and a quick dividing M phase. Both have substages. I-phase represents interphase.

  • The regular sequence of G1, S, G2 (interphase), and M period (mitotic phase) is called the cell period. 
  • Interphase is called the stage that is resting, but it’s a period of great activity. 

Three procedures that are important, which are preparatory to the cellular unit, take place during the interphase. Hence, it is also known as the preparatory stage. These processes are: 

  • Replication of DNA along utilizing the synthesis of nuclear proteins such because of the histones 
  • In animal cells, duplication of centrioles takes place by the outgrowth of daughter centrioles through the parent centrioles, which are at a right angle to each other. 
  • Synthesis of embryo substances which can be rich and provide energy for mitosis, And synthesis of proteins at the end of interphase 

M Phase

 

Mitosis

Mitosis is a type of cellular division by which chromosomes of parent cells are duplicated (by replication of DNA) and equally distributed (quantitatively and qualitatively) into two child nuclei. The term mitosis is derived from Greek, which Ek Word “Mitos” means fibril or thread.

Strassburger initially observed mitosis in plant cells (1870) and Boveri and Flecellsg in animal cells (1879). The term was coined by Flemming in 1882. It can also be called equational division, as a result of circulation that is equal to in daughter nuclei. It is not known as a somatic cell unit due to its occurrence in its somatic cells. It’s about 1-5% of the duration that is the total cycle. Based on different types of cells plus the species, mitosis takes 30 minutes to 3 hours for completely meristematic regions meristematic the sites of mitosis e.g., root ape, shoot apex, intercalary meristem, lateral meristem, leave, flowers, fruits, embryo, seeds, etc. 

Mitosis is completed in two steps, karyokinesis, and cytokinesis. 

Karyokinesis

Mitosis starts utilizing the division that is nuclear of cell known as karyokinesis (Gk, karyon -nucleus, kinesis – movement). The four stages of karyokinesis are prophase, metaphase, anaphase, and telophase. Prophase (Gk Pro-first, stage –stage) is often divided into three substages – early prophase, mid-prophase, and prophase that is late. It is the stage that is first proper. It’s The phase that is the longest of Karyokinesis. 

Early prophase 

  • In this substage the nucleus and cell become spheroid and the nucleus appears as a ball of wool. Chromatin fiber condenses to make an elongated chromosome, Which increases refractivity and viscosity of cytoplasm. 
  • In animal cells, duplicated centrioles. (S stage of interphase) start to go towards opposite poles of the cell. Each centriole radiates out fine microtubular fibrils called astral rays. In animal cells and cells of lower flowers, fibrils seem like spokes of a wheel around each centriole to make an aster. 

Mid-prophase 

In mid-prophase, chromosomes shift towards the periphery and then leave a clear central area. It becomes shorter and thicker. Each chromosome consists of Two threads that are longitudinal chromatids. Both chromatids are attached by the centromere, and so are known as sister chromatids. 

Late prophase 

In this substage, spindle fibers start showing up around the nucleus. The size of chromosomes is much reduced as compared to the prophase, which is early. Spindle poles are formed without asters in plant cells, sufficient reason for asters in animal cells. 

Nucleolus and other cell organelles (like mitochondria, Golgi complex, ER, vacuoles, etc.) disappear. The presence of the spindle is essential for mitosis. If cells are treated with colchicines, which inhibit spindle formation, the anaphasic movement of the two groups of chromosomes towards the poles doesn’t just take place. 

Prometaphase 

  • Prometaphase (Gk Pro- before, meta-second, phase stage that is– is the intermediate stage of metaphase and prophase and hence acts as a connecting link between them. The nuclear membrane completely degenerates in this stage. So the mixing of cytoplasm with nucleoplasm occurs. It is understood as extranuclear mitosis or mitosis. 
  • In many protozoa, fungi, and some animal cells, the nuclear membrane does perhaps not degenerate throughout cell division known as intranuclear or premitosis. 
  • A spindle fiber consists of 4-20 microtubules formed of the protein tubulin. Spindle converge that is fiber two end or poles. It has the maximum diameter in the middle, known as the equator. 

Metaphase

  • In metaphase (Gk meta-after or phase that is the second stage) discontinuous fibers radiate out from two poles and get connected to the disc-shaped framework at the top of the centromere called kinetochores. A kinetochore is a complex protein structure that is analogous to the ring for the microtubule hook; it’s the point where microtubules connect on their own to the chromosome. Chromosomes or kinetochore fibers contract and bring chromosomes over the equator, this occurrence is called congression. 
  • Smaller chromosomes are directed towards the center while bigger ones are peripheral in position on the equator. The centromeres of all of the chromosomes lie on the equator forming a plate that is an apparent metaphasic or equatorial serve while hands are directed towards the poles. 
  • The kinetochores have two functions. The primary function is the known fact that they serve for the attachment of microtubules of the chromosomal spindle fibers. They might also be involved in the formation of the chromosomal Spindle fibers during metaphase and prometaphase by serving as centers for polymerization of the protein of microtubules. 
  • Metaphase is the best phase to count the total wide range of chromosomes in just about any species and details the study of the morphology of chromosomes. Idiograms (arrangement of chromosomes in a series of decreasing size) are drawn in this stage. 

Anaphase  

In anaphase (Gk ana – up, phase stage, that is– chromosomes are arranged on the equatorial plate for a short period. The centromeres of chromosomes start to divide into two, forming daughter chromosomes with a centromere in each. Daughter chromosomes are repulsive, therefore, migrate towards contrary poles. Spindle fibers attached to the centromeres shorten and pull the chromosomes to your poles. The velocity of anaphasic motion does perhaps not be determined by the size associated with the chromosomes. In the anaphasic movement of chromosomes, the centromeres lead the trail while the limbs trails behind. So anaphasic Chromes, the centromeres, lead the path as the limbs trail behind. 

At the end of anaphase, two groups of chromosomes are formed, one at each pole. The amount and kinds of chromosomes at each pole match in the parent nucleus. 

Telophase 

  • During telophase (Gk. Telos-end, phase –stage) of mitosis viscosity of cytoplasm decreases. A fresh membrane that is nuclear, is formed (either from an older Nuclear ER or envelope) around each pair of chromosomes. Chromosomes overlap one another, and chromatin is developing. The organizer that is nuclear of satellite chromosomes produces nucleolus for each daughter nucleus. Nucleoplasm surrounds a certain section of chromatin. They declare that is gel is converted into a sol state and disappears. 
  • In this manner, two child nuclei are formed at the poles of the spindle. Hence, this period is just the reverse of the prophase. Golgi complex and reticulum that is endoplasmic are reformed.

Cytokinesis

Cytokinesis begins either by constriction or cleavage. Mitosis ends with the division of cytoplasm known as cytokinesis. It’s derived from the Greek word “to” which means hollow or cell, “kinesis: which means movement. It starts towards the center of anaphase and is finished with the telophase. It 89 is different in animals and flowers. If nuclear division occurs without cytoplasmic division, a syncytium is formed. 
 

Frequently Asked Questions

Question 1: How do you understand the cellular cycle?

Answer:

The cell period refers to the series of events that results in the replication associated with the cell along with the DNA.

Question 2: What would be the four major stages of mitosis?

Answer:

The four important stages of the cell period include:

  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis

Question 3: What are the various phases of a cellular cycle?

Answer:

  • The different stages of the cell cycle include the Interphase – this phase includes the G1 phase, S phase as well as G2 phase.
  • M phase – This is the mitotic phase and is split into prophase, metaphase, anaphase, and telophase.
  • Cytokinesis – In this phase, the cytoplasm regarding the cell divides. 

Question  4: Who discovered the cell cycle?

Answer:

Walther Flemming discovered the cell cycle in the century that is 19th. He was a professor at the Institute of Anatomy.

Question 5: Which can be the stage that is most important in the cycle?

Answer:

Interphase is essential to the cycle. The cell stays within the interphase for optimum periods. The cell makes itself for division during this phase. The cell undergoes cell replication and growth during this phase.

Question 6: What is the need for the G1, S, and G2 phases of this interphase?

Answer:

  • The cell continues to grow but does not replicate during the G1 phase.
  • The DNA of the cell replicates through the S period.
  • The RNA, proteins, and other macromolecules needed for the mitotic units are manufactured by the cellular during the G2 period.

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