This document summarizes the cell cycle and its regulation. It describes that the cell cycle consists of interphase and M-phase. Interphase includes G1, S, and G2 phases where the cell grows and duplicates its DNA. M-phase is where the cell divides. Regulation occurs through cyclins, cyclin-dependent kinases (CDKs), and checkpoint proteins that control phase transitions. CDK activity is regulated by binding with cyclins to form active complexes, or being inactivated through phosphorylation. Precise coordination of these elements ensures orderly cell division and replication.

1. By
Ritisha Gupta

2. • Cell division is very important process in a living organisms. During the division of a cell, DNA replication and cell growth also
tales place.
• All the processes, i.e., cell division, DNA replication, and cell growth, hence have to take place in a coordinated way to ensure
correct division and formation of progeny cells containing intact genomes.
• Although growth (in terms of cytoplasmic increase) is a continuous process, DNA synthesis occurs only during one specific stage in
the cell cycle.
• The replicated chromosomes (DNA) are then distributed to the daughter nuclei by a complex series of events during cell division.
These events are themselves under genetic control. Complete life cycle is called as cell cycle.

3. There are 2 phases of cell cycle :-
1. Interphase
2. M-phase

5. The most active phase of the whole cell cycle.
Constitutes 95% of whole cell cycle.
It is the preparatory phase for cell division.
In interphase metabolism of cell increases. A series of metabolic changes
occurs during interphase in cell. These changes are not visible under
microscope, so some scientists termed interphase as resting phase.

6. Howard and Pelc classifieds interphase into 3 subjects categories.
1. G1 phase or Pre DNA synthesis phase (1st gap phase)
2. S phase (DNA Synthesis phase)
3. G2 phase (2nd Gap phase) or Post DNA synthesis phase (Pre mitosis
phase).

7.  G1 phase also known as pre synthetic phase as it occurs between mitosis and initiation between
DNA replication,
 During this stage cell is metabolically active and continuously grows.
 Cell organelle increase and rapidly synthesizes different types of RNA and proteins.
 As now proteins are available, so synthesis of new protoplasm takes place and start growing in
size.
 Cell grows maximum in this phase.

8. Replication of nuclear DNA and synthesis of histone protein.
The DNA amount becomes double.
Note: Amount of DNA becomes double but Chromosome
duplication do not takes place.

9. Occurs during this phase.
Proteins are synthesized in Final preparation of M- Phase
preparation for mitosis Example- formation of Tubulin Protein
which is required for spindle fibres formation while cell growth
continues.

10. 0
0.5
1
1.5
2
2.5
3
3.5
4
M PHASE G1 PHASE S PHASE G2 PHASE

11. IT HAS 4 PHASES :
1. •Prophase
2. •Metaphase
3. •Anaphase
4. •Telophase

12. •Centrioles which had
undergone duplication
during S-Phase start
moving towards the
opposite pole.
•End of prophase do not
show golgi apparatus,
Endoplasmic nucleus and
nuclear envelope.

13. •Best stage to
study morphology
of chromosome.
•Disintegration of
nuclear envelope

15. •Also known as
reverse prophase.
•Cytokinesis takes
place which starts
in late anaphase.

17. HOW THE CELL IS
CONTROLLED? IS IT ONLY THIS
MUCH? WITHOUT ANY
PREPARATION HOW CAN IT BE
DONE?
PREPARATION FOR THIS IS
ALSO NEDED. THIS ALL WILL
BE TAUGHT TO YOU IN THE
TOPIC CELL REGULATION ,
CHECK POINTS AND
PROTIENS REQUIRED FOR
THIS.

18.  Leland and H. Hartwell, R. Timothy Hunt and Paul M. Nurse won the
2001 Nobel Prize in Physiology or Medicine for the discovery of the
central molecules like cyclins and cyclin dependent kinase (CDKs).
 Nurse, T. Hunt and Hartwell in 2001 studied cell cycle in
sachcharomyces (Baker yeast).

19.  The cell cycle has major 3 check points
1. First check point- Late G1 check point
2. Second check point- Late S check point
3. Third check point- Metaphase or anaphase transition
point
Regulation in a cell cycle at check points occour
using regulatory proteins such as CYCLIN, CYCLIN-
Dependent kinase, ANAPHASE-Promoting complex, and
many other proteins.

22. Phosphorylates the Threonine or Serine
Residues of its target protein.
Phosphorylated proteins in turn result in the
initiation or regulation of major cell cycle
events such as replication (S phase), mitosis,
and cytokinesis (M phase).
But the phosphrylation role of CdK is
mediated by Cyclin. cyclin combines with Cdk
forming an active cyclin- Cdk
complex(CCC).CCC is functional only in

23. There are 3 types of Cyclin , depending on
the phases of cell cycle at which they
function:
a) G1/S cyclin, which binds to the CdK at the
end of the G1 and function in the S phase
by promoting DNA Synthesis.
b) S cyclin, which binds to the CdK in the
Sphase and stimulates DNA replication
c) M cyclin, which binds to CdK in the M phase
and promotes mitosis.

24. Regulation includes:-
1.Activation of cyclin-CdK
complex
2.Inhibition of cyclin-CdK
complex

25. •The activity of CDK is regulated
by the formation or dissociation
of CCC.
•The active site of CdK is a cleft
blocked by a T-loop.
•Binding of cyclin with CdK
dislocates the loop and exposes
the active site, forming CCC.
•Phosphorylation of threonine
residue induces changes in the
loop and forms completely active
CdK, capable of phosphorylating
the proteins involved in the cell
regulation. .

26. •CdK contains tyrosine
residue at the roof of
active site which is
the site of inhibition .
•An enzyme called wee
1 kinase
phosphorylates the
tyrosine, leading to
the inactivation of

27. Done with the help
of CAK CdK
activating kinase .
CAK
dephosphorylates
the roof of active
site and reactivates
the CCC.

29. In cancer cells check points do not work
properly leading to uncontrolled division.
The total heredity material which occur
outside the chromosome is called
plasmogene.
Some cells in adult animals do not
appear to exhibit division are heart cells
The cells which do not divide in Go phase
are neurons.

30. Thank you
For any query or doubts mail me at-
ritisha.gupta9719@gmail.com
Ritisha
Gupta