• Every cell in our body produced by a pre-existing cell.
  • process of cell formation from pre-existing cells is known as the cell cycle.
  • Involves in many repetitions of cellular growth and reproduction, nuclear division.
  • Almost all the living cells undergo a cell cycle (some exceptions like RBC).
  • The cell cycle is separated into two phases:
  • Interphase and mitosis

Different stages of the mitotic cycle and time duration:

Part of cell cycle Phase Description of phase Duration hr. (humans)
Interphase G1 Pre-DNA-synthesis 12
S DNA-synthesis phase 10
G2 Post-DNA synthesis phase 3
Mitosis M Mitotic phase 1


  • Interphase of a cell cycle includes three-phase:
  • G1 phase, S phase, and G2 phase.

G1 phase

  • After the completion of a cell cycle, the daughter cell begins the G1 phase of the new cell cycle.
  • G1 is the resting phase.
  • It is named as first gap phase.
  • No DNA synthesis takes place during this stage.
  • It involves the synthesis of RNA.
  • During this phase, chromatin is fully extended.
  • G1 involves transcription of rRNA, tRNA, and mRNA.

S phase (Synthesis phase)

  • Replication of DNA starts.
  • Synthesis of histone protein starts.
  • S phase occupies 30-35% of the cell cycle.

G2 phase

  • This a second gap or growth phase.
  • During this phase, the synthesis of RNA and protein.
  • Restores energy.
  • It takes 10-25% time of the cell cycle.


  • In Latin mito: threads.
  • During the mitosis process, the nuclear material becomes visible and appears like threadlike chromosomes.
  • Occurs in Somatic cells for the growth of cell number during embryogenesis and blastogenesis in plants, and animals.

M phase is split into the following steps:

Prophase (pro: before, phasis: appearance)

  • The nuclear membrane starts disappearing.
  • Formation of spindle fibers.
  • Each chromosome of prophase is consisting of two coiled filaments.(Chromatids).
  • The region where two chromatids joined is known as Centromere.
  • Formation of sister chromatids.
  • Cells become spheroid, more refractile, and viscous.
  • During prophase, microscopic bodies are called Centrioles.
  • Causes by an increase in cytosolic Ca2+  

Prometaphase, Metaphase (Gr: meta: after, phasis: appearance)

  • Breakdown of the nuclear envelope.
  • Chromosome line up at the center of the cell.
  • Spindle fiber interacts with chromosomes.
  • When centrioles reach to poles of the cell, they’re surrounded by series of radiating microtubules recognized as Aster.
  • The region where spindle fibers attached to the centromere acknowledged as kinetochore.

Anaphase (Gr: ana: up)

  • Spindle filer pulls the chromosomes towards opposite poles.
  • Splitting of the chromosomes into its sister chromatids (daughter chromosomes).
  • Each daughter chromosomes having one kinetochore.


  • Chromosomes finally reach the opposite poles.
  • Nuclear envelope reforms.
  • The disappearance of spindle fibers.


  • Process of the division of cytoplasm.
  • Formation of two separate cells.
  • Cytoplasm divides by a process recognized as Cleavage.
  • puckering and furrowing of the plasma membrane is the first sign of cleavage in an animal cell.
  • Cell pinch apart in animal cell and plant cell plate become the new cell wall
  • In-plant cell cytokinesis occurs by other different processes due to a rigid wall.
  • Cleavage doesn’t occur in plant cells.
  • Formation of the Daughter cell.
  • Daughter cells have a full set of chromosomes which is identical to the mother cell.


  • The number of centrosomes in animal cells?
  • Purpose of mitosis?
  • The process of nuclear division is known as?


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