Cell Cycle

Definition
An orderly sequence of events in which one cell divides and forms daughter cells and the daughter cell again divides is called cell cycle.
OR
Round of cell growth and cell division is known as cell cycles.
Phases of Cell Cycle
Cell cycles consist of two phases
1. Inter Phase Or Resting stage or (non-division)
2. Division Phase
1. Inter Phase
The period of the cell cycle between two consecutive divisions is called Interphase.
OR
The phase of cell cycle in which the cell cannot be divided but perform its metabolic function for the preparation of its division are called Interphase.
Sub – Stages of Interphase
Inter phase divide into three sub-stages.
i. G1 – Stage
ii. S – Stage
iii. G2 – Stage
i. G1 – Stage

• The inter phase begins with this phase.
• Enzyme for the formation of DNA is produced.
• During this stage cell grows rapidly by synthesis of protein and cytoplasmic organelles.
• Duration of G1 is about 25-50% of Interphase.

ii. S – Stage (synthesis stage)

• In this stage synthesis of DNA occurs and numbers of chromosomes become double.
• Duration of s-phase is 35-40% of Interphase.

iii. G2 – Stage

• It is the end stage of Interphase.
• In this period, production of protein and microtubules occur that are required for cell division.
• Numbers of mitochondria also increase for energy production.
• The size of cell becomes doubled and cell starts division.

Duration of Cell Cycle

• Human Cell (animal cell)
• 18-24 hours for cell cycle
• Mitosis 30 minutes
• G1 phase 9 hours
• S phase 10 hours
• G2 phase 4.5 hours

Plant Cell

• 10-30 hours for cell cycle

2. Division Phase
This phase involves actual cell division and consists of two stages.
Karyotinesis
Cytokinesis
Karyokinesis
Division of nucleus is called as karyokinesis.
Cytokinesis
Division of cytoplasm is called as cytokinesis.