Cell Cycle

1. CELL CYCLEGuided by:
Dr . Kaushik Ku. Panigrahi
Presented By:
Sangeeta Meher
Adm No. 14C/15
2nd year B.Sc.(Ag)

2. WHAT IS CELL CYCLE ?
 The cell cycle is the sequence of events that takes place in cells. It
leads to cell division and replication (duplication).
 In prokaryotes, the cell cycle is through the process of binary fission.
 In eukaryotes, the cell cycle can be divided into two phases -
interphase and mitotic phase.
 Interphase is the stage during which the cell prepares, grows and
accumulates nutrients needed for mitosis and also duplicates the
DNA.
 In the mitotic phase, the cell splits itself into two distinct cells known
as 'daughter cells' and the final phase is cytokinesis, where the newly
formed cells are completely divided.

3. STAGES OF CELL CYCLE:
 There are four distinct phases in the cell cycle - G1 phase, S
phase (synthesis), G2 phase and M phase.
 The G1, S phase and G2 phase together are known as
interphase.
 The cells that have stopped dividing temporarily or reversibly
are said to be in the state of quiescence called G0 phase.
Progression from phase to another depends on the proper
completion of the previous one.

5. Go PHASE:
 Sometimes the cells in the quiescent and senescent cells
are referred to as post mitotic.
 The cells which are indivisible in multicellular eukaryotes
generally enter the quiescent Go state from G1. They may
remain in the quiescent state for long periods of time.
 This state can be for indefinite like in neurons and is very
common in cells that are fully differentiated. Death of the
cells in response to damage of DNA or degradation would
make the progeny of the cells nonviable. Some cells like the
cells of liver and kidney enter the Go phase semi-
permanently.

6. INTERPHASE:
 Earlier to the cell division process, the cell needs to accumulate
nutrients. During the interphase all the preparations are done.
 Interphase proceeds in a series of three stages, G1,S, and G2.
Division of cell operates in a cycle, hence the interphase of the
cycle is preceded by the previous cycle of M phase and
cytokinesis.
 Interphase is also called the preparatory phase. In the interphase
stage the division of nucleus and cytosol does not occur. The cell
prepares for division
 This is a stage between the end of mitosis and start of the next
phase. significant event that occurs is the replication of genetic
material.

7. G1 PHASE :
 This is the first phase in the interphase. From the end of the
previous M phase till the beginning of the DNA synthesis in
the next cycle is called the G1 phase. This phase is also called
growth phase .
 In this phase there is a marked production of proteins by the
use of 20 amino acids, also enzymes that are required in S
phase needed during DNA replication takes place .
 During G1 phase, the cell grows physically larger, copies
organelles, and makes the molecular building blocks it will
need in later steps .

8. S PHASE:
 The start of the S phase is when the DNA replication commences.
When the phase completes all the chromosomes have been
replicated.
 Each chromosome has two sister chromatids. During this phase,
the amount of DNA in the cell is doubled but the ploidy of the cell
remains unchanged.
 It also duplicates a microtubule-organizing structure called the
centrosome .
 The centrosomes help separate DNA during M phase .

9. G2 PHASE:
 It is the gap phase which happens during the gap between the
DNA synthesis and mitosis.
 During this phase the cell will continue to grow , makes
proteins and organelles, and begins to reorganize its contents
in preparation for mitosis.
 this phase ends when mitosis begins enter the M (mitosis)
phase and divides.

10. Mitotic phase:
 During the mitotic (M) phase, the cell divides its copied DNA and
cytoplasm to make two new cells. M phase involves two distinct
division-related processes: mitosis and cytokinesis.
 In mitosis, the nuclear DNA of the cell condenses into visible
chromosomes and is pulled apart by the mitotic spindle, a
specialized structure made out of microtubules.
 Mitosis takes place in four stages: prophase (sometimes divided
into early prophase and prometaphase), metaphase, anaphase,
and telophase.
 As in both G1 and G2, there is a check point (metaphase
checkpoint) that ensures the cell is ready to complete cell division
.

12. CYTOKINESIS:
 The cytoplasm of the cell is
split making two new cells .
 Cytokinesis usually begins
just as mitosis is ending,with
a little overlap .Cytokinesis
takes place differently in
animals and plants .

13. THANK YOU