The document summarizes key aspects of the cell cycle and its control mechanisms. It describes the main phases of the eukaryotic cell cycle - G1, S, G2, and M phase. It explains that cyclins and cyclin-dependent kinases (CDKs) control progression between phases by promoting specific events like DNA replication and mitosis. CDK activity is regulated by binding with cyclins and proteolytic degradation of cyclins by the anaphase promoting complex. Checkpoints in the cell cycle arrest progression under negative intracellular signals to ensure DNA replication and chromosome separation are properly completed.

1. DIGITAL ASSIGNMENT
CELL BIOLOGY AND BIOCHEMISTRY
BY : MANSI GHATIYA
17BCB0012

2. CELL CYCLE AND CELL CONTROL

3. THE CELL CYCLE

4. THE EVENTS OF EUCARYOTIC CELL
DIVISION

5. Cell cycle is of 2 types : 1) MITOSIS
2) MEIOSIS
MITosis takes the cell and Makes It Two (diploid).
Meiosis has to do with sex.
From the cell’s point of view :
- mITosis results in Identical Twins.
- mEioSis results in Egg and Sperm (haploid).

6. THE PHASES OF THE CELL CYCLE

7. G1 – post mitotic phase.
RNA and protiens are synthesized.
No DNA synthesized.
S – Synthetic Phase.
DNA is formed from purines and pyrimidines.
DNA content of nucleus is doubled.
G2 – Pre mitotic gap phase.
synthesis of RNA and protien
DNA synthesis stops.
M – Prophase , Metaphase , Anaphase , Telophase , Cytokinesis.

8. THE CONTROL OF THE CELL CYCLE

9. CONTROL OF THE CELL CYCLE
G1 phase events :
- G1 cyclins signals the cell to prepare the chromosomes (DNA) for
replication (occurs in S-phase)
S phase events :
-S-phase promoting factor (SPF) (the complex of S-cyclins + S-phase CDK)
prepares the cell to enter S phase and promote duplication of DNA (and its
centrioles)
-as DNA replication continues, one of the cyclins shared by G1 and S-phase
CDKs (cyclin E) is destroyed
G2 phase events :
M- cyclins begin to rise in the end of G2 phase to prepare the cell into
mitosis

10. M phase events - early stage :
• M-phase promoting factor (MPF) (the complex of M-cyclins + M-phase
CDK) initiates events leading the cell from prophase to the metaphase of
mitosis:
–assembly of the mitotic spindle
–breakdown of the nuclear envelope
–condensation of the chromosomes
Meiosis (particularly meiosis I, meiosis II - is essentially a mitosis) requires
special controls; some of them are similar to those in mitosis, e.g. APC and
MPF (maturation-promoting factor for its role in meiosis I and II of
developing oocyte

11. M phase events - late stage :
A-phase promoting complex (APC) is activated by M-phase promoting
factor and :
– destroys the M-phase cyclins by ubikvitination (conjugating them with
the protein ubiquitin which targets them for destruction by proteasomes)
– allows the sister chromatids at the metaphase plate to separate and move
to the poles during anaphase.
– turns on synthesis of G1 cyclins for the next turn of the cycle .
– degrades geminin, a protein that has kept the freshly-synthesized DNA in
S phase from being re-replicated before mitosis.

12. THE CONTROL SYSTEM CAN ARREST THE
CELL CYCLE AT SPECIFIC CHECKPOINTS

13. CHECKPOINTS GENERALLY OPERATE THROUGH
NEGATIVE INTRACELLULAR SIGNALS
• The Cell-Cycle Control System Is Based on Cyclically
Activated Protein Kinases
• Cdk Activity Can Be Suppressed Both by Inhibitory
Phosphorylation and by Inhibitory Proteins
• The Cell-Cycle Control System Depends on Cyclical
Proteolysis
• Cell-Cycle Control Also Depends on Transcriptional
Regulation

14. TWO KEY COMPONENTS OF THE
CELL-CYCLE CONTROL SYSTEM
• G 1 /S-cyclins bind Cdks at the end
of G1 and commit the cell to DNA
replication.
• S-cyclins bind Cdks during S phase
and are required for the initiation of
DNA replication.
• M-cyclins promote the events of
mitosis.
• G 1 -cyclins, helps promote passage
through Start or the restriction point in
late G1.

15. CORE OF THE CELL-CYCLE CONTROL
SYSTEM

16. THE STRUCTURAL BASIS OF CDK
ACTIVATION

17. REREPLICATION BLOCK.

18. THE CREATION OF A G1 PHASE

19. AN OVERVIEW OF THE CELL-CYCLE
CONTROL SYSTEM

20. CONTROLLERS OF THE CELL CYCLE
The paasage of a cell through the cell cycle is controlled by protiens :
1. CYCLINS – their levels in the cell fluctuate rise and fall with the stages
of the cell cycle.
G1 cyclins , S-phase cyclins , M-phase cyclins.
2. CYCLINS – DEPENDENT KINASES (CDKs) – their levels in the cell
remain stable bind and activate the appropriate cyclin fosforylate variety
that control cell cycle.
G1 CDKs , S-phase CDKs , M-phase CSKs.
3. The anaphase – promoting complex (APC) and other proteolytic
enzymes – events leading to destruction of cohesins , thus allowing the
sister chromatids to separate. Degrades the mitotic (M-phase) cyclins.

21. THANKYOU