The document discusses the genetic regulation of the cell cycle, focusing on the roles of internal factors such as kinases and cyclins. It highlights the positive regulation through cyclins and cyclin-dependent kinases (cdks) that control the timing of cell cycle phases and the correlation between cyclin levels and cell cycle checkpoints. Additionally, it addresses negative regulators like the retinoblastoma protein (Rb) and p53, which also play critical roles in the regulation of the cell cycle.

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