Each step of the cell cycle is monitored by internal controls called checkpoints. There are three major checkpoints in the cell cycle: one near the end of G1, a second at the G2/M transition, and the third during metaphase. Positive regulator molecules allow the cell cycle to advance to the next stage.

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 CHECKPOINTS

2. INTERPHASE
• Cell prepares for division by undergoing
Cell growth
DNA replication
• More than 95 ٪of the duration of cell cycle
• Nerve cells remain in cell cycle

3. • Also called “Gap1 Phase”
• Interval between mitosis and initiation DNA replication
• Cell is metabolically active and grows continuously
• RNA, proteins, amino acids all energy rich compounds
are synthesized
• Organelles are replicates(Except centrosome)
G1 PHASE

4. S PHASE
• Also called “Synthesis phase”
• DNA synthesis of replication takes place
• DNA per cells double
DNA replication – nucleus
Centriole duplication – cytoplasm

5. G2 PHASE
• Also called Gap2 phase
• Proteins are synthesized to prepare for Mitosis
• Cell growth continues

6. M PHASE
• M stands for Mitosis
• Also called Equational phase
• Begins with nuclear division
• ( Karyokinesis )
• Ends with division of cytoplasm
(Cytokinesis)
95% of
Interphase
5% M phase

7. Source : Microbe notes

8. • In between the G, and S phase.
• It checks the damage of DNA and replication errors.
• At the G, checkpoint cell checks the external and
internal conditions for the division.
G1 checkpoint

9. • In between G, and M phase.
• This checkpoint make sure that cell division goes
smoothly and produces healthy daughter cell with
undamaged DNA.
• If any error or damaged detected cell will pause at G2
checkpoint and allows for repair.
G2 checkpoint

10. • It is known as spindle checkpoint.
• This checkpoint ensures that sister chromatids are
currently attached to the spindle microtubules.
• Cell cycle regulated by an enzyme called cyclin
dependent protein kinase.
• Cyclins are proteins that activate the protein kinase for
the regulation of eukaryotic cell cycle.
M checkpoint

11. CONCLUSION
As a cell moves through each phase, it also passes through
several checkpoints. These checkpoints ensure that mitosis
occurs only when environmental conditions are favorable
and the cellular genome has been precisely replicated
Cell cycle checkpoints are surveillance mechanisms that
monitor the order, integrity, and fidelity of the major events
of the cell cycle.

12. REFERENCES
1. Grana and Xavier, et al.(1995) Cell cycle control in mammalian cells: cell
cycle and check points, (11)2: 211-220.
2. Lim, Shuhui, and Philipp Kaldis.et al.(2013) “Cdks, cyclins and CKIs: roles
beyond cell cycle regulation.” Development (140)15: 3079-3093.
3. G. Prem Veer.(1994)Cell cycle: regulatory events in G1→ S transition of
mammalian cells. Journal of cellular biochemistry, (54)4: 379-386.