THE CELL CYCLE

The period from the time a cell is produced until it completes mitosis is called cell cycle. Cell division occurs during growth and repair processes. Cell cycle has following basic stages:

(n) Mitosis: It is the division of the nucleus.

(b)  Cytokinesis: It is the division of the cytoplasm.

(c)   Interphase: The cell grcms and carries out its various metabolic processes during interphase.

The cell cycle is divided into following stages:

I. The CI (first growth or gap) phase: It is the early growth phase of the cell.

  1. S (DNA synthesis) phase: During this phase the growth continues. This phase also involves DNA replication.
  2. G2 (second growth or gap): This phase prepares the cell for

division. It includes replication of the mitochondria and other organelles, synthesis of mierotubules and protein. These microtubules and proteins will make up mitotic spindle fibers, and chromosome condensation.

  1. The M (Mitotic) phase: Partitioning of chromosomes and daughter cells take place in NI phase.

INTERPHASE

Interphase occupies 90% of The total cell cycle. It includes the Gi S. and G, phases. Normal acti‘ ides of the cell take place during this phase. DNA replication is completed during the S phase of interphase. Thus Interphase also prepares the cell for division.

An exact copy of the DNA is formed before the cell division. This process is called replication. l’hC double stranded DNA makes a replica, or duplicate, of itself. Each daughter cell receives the same genetic material as the parent cell. Fheretbre, replication is essential. Thus a pair of sister chromatids is !brined. A chromatid is a copy of a chromosome produced bv replication. Sister chromatids are attached by centromere. the centromere is a specific DNA sequence of about 220 nucleotides. The centromere has a specific location on any given chromosome. A disk of protein called a kinetochore is attached to

The period from the time a cell is produced until it completes mitosis is called cell cycle. Cell division occurs during growth and repair processes. Cell cycle has following basic stages:

(n) Mitosis: It is the division of the nucleus.

(b)  Cytokinesis: It is the division of the cytoplasm.

(c)   Interphase: The cell grcms and carries out its various metabolic processes during interphase.

The cell cycle is divided into following stages:

I. The CI (first growth or gap) phase: It is the early growth phase of the cell.


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  1. S (DNA synthesis) phase: During this phase the growth continues. This phase also involves DNA replication.
  2. G2 (second growth or gap): This phase prepares the cell for

division. It includes replication of the mitochondria and other organelles, synthesis of mierotubules and protein. These microtubules and proteins will make up mitotic spindle fibers, and chromosome condensation.

  1. The M (Mitotic) phase: Partitioning of chromosomes and daughter cells take place in NI phase.

INTERPHASE

Interphase occupies 90% of The total cell cycle. It includes the Gi S. and G, phases. Normal acti‘ ides of the cell take place during this phase. DNA replication is completed during the S phase of interphase. Thus Interphase also prepares the cell for division.

An exact copy of the DNA is formed before the cell division. This process is called replication. l’hC double stranded DNA makes a replica, or duplicate, of itself. Each daughter cell receives the same genetic material as the parent cell. Fheretbre, replication is essential. Thus a pair of sister chromatids is !brined. A chromatid is a copy of a chromosome produced bv replication. Sister chromatids are attached by centromere. the centromere is a specific DNA sequence of about 220 nucleotides. The centromere has a specific location on any given chromosome. A disk of protein called a kinetochore is attached to

each centromere. It forms an attachment site for the micro-tubules of the mitotic spindle.

The cell cycle moves into G2 phase, the condensation of chromosomes begins. The cell also begins to assemble different structures during G2 phase. The cell later uses these structures to move the chromosomes to opposite poles of the cell. For example, centrioles replicate, and there is extensive synthesis of the proteins that make up the microtubules.

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