A cell cycle is a series of events that takes place in a cell as it grows and divides. A cell spends most of its time in what is called interphase, and during this time it grows, replicates its chromosomes, and prepares for cell division. The cell then leaves interphase, undergoes mitosis, and completes its division.

1. Genetic Regulation of Cell cycle
Part -2
Dr. Maysaa Abdul Razzaq Dhahi
Microbiology Dept.- College of Medicine
Al-Nahrain University

2. Internal factors
 External factors
trigger internal
factors, which
affect the cell
cycle.
 Two of the most
important internal
factors are kinases
and cyclins.

4. Regulator Molecules of the Cell Cycle
Positive Regulation :
Cyclins and cyclin-
dependent kinases
(Cdks).
Cyclins : Group of
proteins that regulates
the cell cycle by
forming a complex
with kinases.
 CDK: A member of a
family of protein
kinases that regulating
the cell cycle through
phosphorylation.

5. Timing of cell cycle phases
 There is a direct
correlation
between cyclin
accumulation and
the three major cell
cycle checkpoints.
 The sharp decline
of cyclin levels
following each
checkpoint as
cyclin is degraded
by cytoplasmic
enzymes.
Phase Cyclin CDK
G0 C Cdk3
G1 D,E Cdk4,Cdk2,Cdk6
S A,E Cdk2
G2 A Cdk2,Cdk1
M B Cdk1

6. Regulator Molecules of the Cell Cycle
Negative Regulator:
Retinoblastoma
protein(Rb),
p53,
 p21.

7. Negative Regulator :P53

8. Negative Regulator :Rb

9. Thank you