DR Medhat MRCP

Mitosis
Interphase
Phase
G 0
G1
S
G2
M
Criteria/Events
- Is the resting (quiescent) stage with non-dividing cells.
- This may be temporary or permanent.
- Cells can enter G 0 from G1 if they are not preparing for
cell division. This may occur if the cell has reached its
final differentiation.
- Entry to the cycle & start to grow in size are made in G1.
- It is a gap phase () mitosis (M) of the previous cycle &
DNA synthesis (S) of the new cycle.
- It is under the influence of tumor suppressor gene p53.
- Cells with damage to their DNA are arrested in G1.
- G1 phase determines the variability of the cycle length.
- The drivers of cell in this phase are :
In early G1 : mitogens (chemicals that signal the
cell to start dividing)
In late G1 : protein kinases (cyclin & cyclindependent
kinases`CDK`).
- Represents DNA synthesis.
- DNA is synthesized by replication of the existing strand
- Occupies around the 1/3 of total cel cycle.
- The cycle can be arrested here if DNA didn`t replicate.
- The driver to transfer the cell to G2 : cyclin A &CDK2
combination
- Is a gap phase () DNA synthesis (S) & mitosis (M) when
the cell contains twice as much DNA as non-dividing cells
& repair of any DNA errors to prepare the cell for
dividing
- It is the mitotic (not miotic بالك ‏(خد phase.
- 5% of total cell cycle time.
- Cell division results in 2 daughter cells, each of which can
either :
Immediately enter the G1 phase of a new cell
cycle.
Become an inactive resting (G0) , some of them
remains quiescent for sometime then enter G1
phase.
Some specialized cells (e.g nerve cells) don`t
divide again.
Other cells can be triggered by activities e.g
wound repair to enter G1 phase to divide as
required.
Die (cell loss fraction).
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