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What are the two main parts of the cell cycle
The m phase ( mitotic phase) is when mitosis takes place , the cell then divides into two. The M phase is only a relatively short period
Most of the cell cycle is called interphase

Whats the first stage of interphase.
The G1 phase, during this phase, the cell replicates organelles e.g mitochondria, this requires proteins so during G1 a high level of transcription and translation take place.
The size of the cell also increases, this ensures that when the cell divides, the two daughter cells are the correct size.

Whats the second stage of interphase
the Cell passes into The S or Synthesis phase.
During S phase, all of the chromosomes are replicated , to do this , the cell needs to synthesise a great deal of DNA.

What is the third stage of interphase.
Now the cell enter G2 phase
During G2 , the cell replaces energy stores used during the S phase, cell also continues to carry out translation and transcription , any damaged chromosomes are repaired during G2
Cell continues to grow

What happens once cell enters mitotic phase after G2
Undergoes mitosis. During mitosis, the chromosomes are separated into two nuclei,
It then undergoes cytokenesis, during this the cell divides into two.
What is the G0 phase
When cells exit cell cycle, it is called G0 phase.

Why do cells enter G0 phase.
Fully differentiated cells, they stay there for rest of life, e,g neurones in adults
Senescent cells (damaged DNA) , at this stage , cell enters G0 permanently.
Some cells enter G0 temporarily, e.g B memory cells, they can then be triggered to reenter cell cycle during infection.
What is the G1 checkpoint
Before S phase, cell must pass G1 checkpoint, and here the cell checks that it has grown to correct size, and checks for DNA damage, if it satisfied checkpoint, passes to S phase.
What happens at G2 checkpoint
The cell checks for DNA damage, and cell has grown to correct size.
Whats metaphase / spindle checkpoint
Checks that chromosomes are assembled correctly on the mitotic spindle, if this is the case, cell completes mitosis, and procedes through cytokenesis