Cell cycle-Explanation & phase of the cell cycle (zooconcept)

What is cell cycle explain? What are the stages of cell cycle? Explain the full information of cell cycle?


                 Cell cycle


In this article we will discuss about the cell cycle- cell cycle, General characteristics of Interphase cell and nucleus & phase of cell cycle.

Contents:

  1. Cell cycle
  2. Interphase
  3. General characteristics of interphase cell and nucleus
  4. G1 Phase (Post-mitotic gap phase)
  5. S phase (synthesis phase) 
  6. G2 phase (pre- mitotic gap phase)
  7. Regulation of cell cycle

Cell cycle:

The cell cycle is a series of changes that takes place in between a growing cell and its division into two daughter cells. The whole process is a cyclic affair as the cell grows, divides the divided cells grow and go. onto divide again. The duration of the cell cycle varies depending upon the size of the cell. type of the cell, temperature, supply of nutrients, availability of oxygen etc. A typical cell cycle has two distinct phases: (i) a non-dividing interphase, and (ii) a period of cell division (division phase).

Interphase:

Interphase, often mistakenly called as “the resting phase is actually a period of intense growth and high metabolic activities. The synthesis and storage of materials in the interphase is essential for the subsequent cell division. Therefore, it is termed as the preparatory phase. It is often considered as a gap between two successive cell divisions i.e., the interval between the end of telophase and the beginning of the next prophase. Interphase occupies the longest time-span of the cell cycle as cells pass most of their time in this phase. Interphase is permanent in the human nerve cells as the neurons do not divide at all after birth.

General Characteristics of Interphase Cell and Nucleus:

  • The nucleus grows in size and becomes distinct.
  • The cytoplasmic organelles are synthesized and the cell grows to its maximum size.
  • The nucleolus becomes prominent.
  • The chromosomes lie scattered in the nucleoplasm in the form of a reticular network, hence called chromatin reticulum.
  • Synthesis of DNA, RNA and histone proteins.
  • Synthesis of other energy-rich compounds take place.
  • Centrioles divide and are positioned at right angle to each other.
  • The chromosomes exists as a pair of chromatids attached at the centromere.

Phase of cell cycles:

Interphase is divided into three distinct phases namely, G1, S and G2 followed by M phase or mitotic phase.

G1 phase(Post -mitotic gap phase) :

The G1 phase or the first grow phase is characterized by the following events.

  • Synthesis of RNA and proteins.
  • Increase in nuclear volume.
  • Nuclear membrane becomes distinct.
  • The duration of this phase is about 8-10 hrs.
  • DNA synthesis does not take place but the enzymes and other components for replication are organized prior to the event.
  • Alternate condensation and decondensation of chromatin material is observed in eakakryotic chromosomes.
  • The non-dividing nerve cells remain permanently in interphase .They are said to remain in an arrested condition called G o state.
  • The G phase fills up the gap between the end of mitosis and the beginning of S phase.

S Phase (Synthesis Phase):

  • The most important event of this phase is the synthesis of DNA. The amount of DNA in doubled at the end of S phase.
  • It lasts for about 6-8 hrs.
  • Certain factors activate replication units just before DNA synthesis.
  • Synthesis of RNA slows down.
  • Nucleus steadily increases in size.
  • Synthesis of histone protein occurs in this phase.
  • Once the cell has passed through S phase, it is committed for cell division.

G2 Phase (Pre-mitotic Gap Phase):

The G2 phase, also called the second growth phase marks the end of interphase. The following changes occur in G2 phase.

  • The duration of this phase is about 4-5 hrs.
  • Synthesis of rRNA and mRNA occurs in this phase.
  • Replication of mitochondria, formation of other cellular organelles and overall growth of cytoplasm.
  • Increase in nuclear volume.
  • Synthesis of non-histone proteins and energy rich compounds.
  • Synthesis of metabolites which prepares the cell for division.

Regulation of Cell Cycle:

The cell cycle in dividing cells is regulated by certain factors produced in G, phase. A specific group of genes called ‘START control the synthesis of these substances. In addition, phosphorylation of histone proteins is known to speed up the entry of G, nucleus into S phase.

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