STUDY ABOUT CELL CYCLE AND CHECKPOINTS AND IT'S REGULATIONS

1. CENTURION UNIVERSITY, BHUBANESWAR
SCHOOL OF APPLIED SCIENCES
M.Sc. In Zoology
NAME – MUKTA MANJARI SAHOO
REGD NO – 230705180023
SUBJECT- CELL AND MOLECULAR BIOLOGY
TOPIC – CELL CYCLE AND IT’S REGULATIONS

2. CHECKPOINTS

3. G1 CHECKPOINT ( G1 restriction point)
At the G1 checkpoint, a cell checks whether internal and
external conditions are right for division. Here are some of
the factors a cell might assess:
-Size: Is the cell large enough to divide?
-Nutrients: Does the cell have enough energy reserves or
available nutrients to divide?
-Molecular signals: Is the cell receiving positive cues (such
as growth factors) from neighbours?
-DNA integrity: Is any of the DNA damaged?

4. If a cell doesn’t get the go-ahead cues it needs at the
G1 checkpoint, it may leave the cell cycle and enter a
resting state called G0 phase. Some cells-stay permanently
in GO, while others resume dividing if conditions improve.
G2 CHECKPOINT
To make sure that cell division goes smoothly (produces
healthy daughter cells with complete, undamaged DNA), the
cell has an additional checkpoint before M phase, called the
G2 checkpoint. At this stage, the cell will check:

5. -DNA integrity: Is any of the DNA damaged?
-DNA replication: Was the DNA completely copied during
S phase?
If errors or damage are detected, the cell will pause at the
G2 checkpoint to allow for repairs. If the checkpoint
mechanisms detect problems with the DNA, the cell cycle
is halted, and the cell attempts to either complete DNA
replication or repair the damaged DNA.
If the damage is irreparable, the cell may undergo
apoptosis, or programmed cell death. This self-destruction
mechanism ensures that damaged DNA is not passed on to
daughter cells and is important in preventing cancer.

6. M CHECKPOINT
1. This occurs at metaphase.
2. Anaphase-promoting complex (APC) regulates this
checkpoint .This is also called spindle checkpoint.
3. This checks whether all chromosomes are properly
attached to the spindle or not. This also governs the
alignment of the chromosomes and integrity of the
spindles. If there are mistakes then it delays the cell in
entering into anaphase from metaphase.

7. CELL CYCLE REGULATORS
The cell cycle is regulated by cycles.
1.Cyclins
2. Cyclin-dependent kinases (CDKs)
3. Cyclin-dependent kinase inhibitors (CDKIs)
1. CYCLIN :
Their concentration varies during the cell cycle. Cyclins are
the family of proteins which regulates the cell cycle . There
are several types of cyclins that are active in different parts
of the cell cycle and causes phosphorylation of CDK.
There are four basic types found in humans and most other
eukaryotes:G1cyclins, G1/S cyclins, S cyclins, and M
cyclins.

8. The levels of the different cyclins vary considerably across
the cell cycle, as shown in the diagram at right. A typical
cyclin is present at low levels for most of the cycle, but
increases strongly at the stage where it’s needed. M cyclin,
for example, peaks dramatically at the transition from G2 to
M phase. G1 cyclins are unusual in that they are needed for
much of the cell cycle.

10. 2.CYCLIN-DEPENDENT KINSASES (CDKS)
These are a family of protein kinases that regulates the cell
cycle. They are present in all known eukaryotic cells.
In order to drive the cell cycle forward, a cyclin must
activate or inactivate many target proteins inside of the cell.
Cyclins drive the events of the cell cycle by partnering with
a family of enzymes called the cyclin-dependent kinases
(Cdks). A lone Cdk is inactive, but the binding of a cyclin
activates it, making it a functional enzyme and allowing it
to modify target proteins.

12. 3.CYCLIN-DEPENDENT KINASE
INHIBITORS(CDKIS)
CDKI is a protein which inhibits cyclin-dependent kinase
(CDK). Cell cycle progression is negatively controlled by
cyclin-dependent kinases-inhibitors (called CDIs, CKIs or
CDKIs). These are involved in cell cycle arrest at the G1
phase.

13. Are those which control the changes
necessary for cell division. They include:-
Cyclins & Cyclin-dependent
kinases(Cdks)
They include ;-Rb proteins & P53 gene
- Inhibitors of Cdks which are of 2 types
Ink family (Inhibitors of kinases) –P19,P15
CIP family (cdks inhibitory proteins) – P21, P57

14. REFERENCES
1.Allen, .(2019). Freshwater Fishes of Australia. T.F.H
Publications: New Jersey, USA.222(14):pp.124-129