The eukaryotic cell cycle consists of four main phases - G1 phase, S phase, G2 phase, and M phase. In G1, cells grow and prepare for DNA replication. In S phase, DNA replication occurs as the DNA duplicates. In G2, cells continue to grow and prepare for mitosis. M phase consists of mitosis, where duplicated chromosomes separate, and cytokinesis, where the cell cytoplasm divides to form two daughter cells each with an identical set of chromosomes. Checkpoint controls ensure conditions are right before progressing between phases.

1. EUKARYOTIC CELL CYCLE
-Different Phases and Molecular Events
Submitted To: Submitted By:
SOS Biotechnology Deepti Maheshwari
Jiwaji University M.Sc. 1st Semester
JIWAJI UNIVERSITY

2. CONTENTS:
INTRODUCTION
CELL CYCLE
PHASES OF CELL CYCLE

3. INTRODUCTION:
Cell is the structural and functional unit of life.
All cells arise from the pre existing cells, that is,
a new cell comes into existence when the old cell
divides.
Cell division is one of the fundamental
characteristics of a cell.
Cells of all living organisms, ranging from the
prokaryotic bacteria to the eukaryotic mammal,
show repeated rounds of cell growth and division
in a cyclic manner.

4. CELL CYCLE:
Cell cycle refers to the ordered series of
events that lead to the cell division
and the production of two daughter
cells, each containing chromosomes
identical to those of the parental cell.
The cell cycle is marked by two major
chromosomal events:
A. Duplication of chromosomes
(S phase)
B. Segregation of chromosomes and
division of cell into two (M phase)
A.
B.

5. PHASES OF CELL CYCLE:
1) G1 Phase
2) S Phase
3) G2 Phase
4) M Phase
I
N
T
E
R
P
H
A
S
E

6. 1) G1 PHASE AND G2 PHASE:
• These are collectively called as Gap Phase.
• In this phase cells grow and double their mass of
proteins and organelles.
• G1 Phase lies between M and S phase while G2 lies
between S and M phase.
• Extracellular and intracellular conditions are checked
to confirm whether or not they are in appropriate
stage for cell to enter in next phase.
• If the prevailing conditions are
not appropriate, then cell enters a
RESTING STATE called as G0
(G Zero)Phase.
G Zero
Phase

7. 2. S PHASE (Synthesis Phase) :
• Accurate copying of the entire DNA molecule of
each chromosome occurs.
• Chromatin protein associated with the DNA also
gets duplicated.
• At the end of S phase, sister
chromatids remain glued to
each other by the help of
COHESIN protein .
Ring formed
by cohesin
(A) (B)

9. 3) M PHASE:
• Segregation of duplicated chromosomes takes place.
• It is consists of two major events :
A. Mitosis
Prophase Pro- Metaphase Anaphase Telophase
metaphase
B. Cytokinesis:

10. A) MITOSIS:
 Initiates with two chromosomal changes:
a) Chromosome condensation b) Sister chromatid
resolution
 CONDENSIN protein brings about the above two
changes.
 Movement of duplicated centrioles (in S phase) towards
the polar site.
 Formation of mitotic spindle takes place, which is a
bipolar array of microtubules.
 Microtubules are of three types:
 Astral microtubule
 Interpolar microtubule
 Kinetochore microtubule

11. FIG: Three classes of microtubules of mitotic spindle in animal cell

12. Fig A: Diagrammatic representation of
PROPHASE stage
Fig B: Micrographic representation of
PROPHASE stage

13.  Breakdown of the nuclear membrane occurs to
allow the attachment of spindle to the chromatids.
Fig A: Diagrammatic representation of
PROMETAPHASE stage
Fig B: Micrographic representation of
PROMETAPHASE stage

14.  Chromosomes are aligned at the equator of the spindle
poles by the microtubules of mitotic spindle.
Formation of METAPHASE PLATE takes place.
Fig A: Diagrammatic representation of
METAPHASE stage
Fig B: Micrographic representation of
METAPHASE stage

15.  Chromosome segregation occurs.
 Completes in two stages:
Kinetochore
microtubule
Spindle
pole

16. Fig A: Diagrammatic representation of
ANAPHASE stage
Fig B: Micrographic representation of
ANAPHASE stage

17.  Disassembly of the mitotic spindle occurs.
 Reformation of nuclear envelope takes place.
Fig A: Diagrammatic representation of
TELOPHASE stage
Fig B: Micrographic representation of
TELOPHASE stage

18. B) CYTOKINESIS:
 Cytoplasm and cell organelle get divided and
distributed to the newly formed daughter cells.
Fig A: Diagrammatic representation of
CYTOKINESIS stage
Fig B: Micrographic representation of
CYTOKINESIS stage

19. • Cytokinesis in plant cell: • Cytokinesis in animal cell:
Chromatids
Contractile
ring made
of actin and
myosin
Microtubule
(A) (B)

20. REFRENCES:
• Molecular Biology Of The Cell (5th Edition) by Bruce
Alberts (page no. 1054-1090)
• Molecular Cell Biology (7th Edition) by Harvey Lodish
(page no. 804)
• The Cell a molecular Approach (4th edition) by
Geoffrey M.Cooper (pg no 677- 680)