The document summarizes the cell cycle, which includes interphase consisting of G1, S, and G2 phases and the M phase. Interphase makes up 95% of the cell cycle and involves cell growth and DNA replication. The M phase is when mitosis and cell division occur. The cell cycle is tightly regulated by checkpoints and a control system involving cyclins and CDKs. Errors in regulation can lead to diseases like cancer.

1. K.G. ARTS & SCIENCE COLLEGE RAIGARH (C.G.)
Year - 2019-20
Deparment of zoology & research center
Subject :- Molecular and cell Biology
Seminar topic:- The cell cycle
Guided by:- Submitted by:-
Proff. Anita Pandey mam. Surendra Patel
M.Sc sem I zoology

2. SYNOPSIS:-
1. Introduction
2. Definition
3. Phase of cell cycle
(A) Interphase
• G1 Phase
• S Phase
• G2 Phase
(B) M Phase
• Mitosis
• Miosis

3. 4. Defrence Between Miosis & Mitosis
5.Cell Cycle Control System
6. Trigger the major process of cell cycle
7. Cell cycle checkpoint
8. Regulation of cell cycle
9.Conclusion
10 Refrence

6. 1. Introduction :-Cell division is very important process in all
living oraganism. During the cell divison DNA replicate and cell
growth take also place.
According to German pathologist Rudolf Virchow in 1858 “Where
a cell arises, there must be a previous cell , just as animals can
only arises from animals and plants from plants.”
“The dream of every cell is to become two cells.” by Francois Jacob
The cell division cycle is a vital process by which a single celled
fertilized egg developed into a mature organism as well as the process

8. by which hair, skin, blood cells and some internal organism are
renewed.
2. Definition :- The sequence of events by which a cell duplicate,
synthesis the other constituents of the cell and eventually divided into
two daughter cell is termed cell cycle.
Formation of new cell by dividing and
duplicating by other cell is called cell cycle.
3. Phases of cell cycle :- In human and other eukaryotes the cell
takes 24 hours to complete the cell cycle. However, this duration of cell
cycle can vary from organism to organism and also from cell type to cell
division. For example :- Yeast can process through the cell cycle in only
about 90 minutes.

9. (A) Interphase :- ◆ It is also called
preparatory phase.
◆ Interphase represent the phase
beween two succesive M phase.
◆ It’s largest phase of cell cycle.
◆ It takes 95% of time of the cell cycle.
Interphase completed in 3 sub-phases :-
(i) G1 Phase :- ◆ It’s a first stage of interphase.
◆ Also called gap 1 or growth 1 phase.
◆ G1 phase takes 11 hours out of 24 hours of cell cycle.
◆ During G1 phase the cell is metabollically active and countinously
but doesn’t replicate it’s DNA.

10. In G1 phase a cell has 3 option :-
◆ To continue cell cycle and enter S phase.
◆ Stop cell cycle and enter G0 phase for undergoing diffrentiation.
◆ Become arrested in G1 phase, hense it may enter G0 phase or re-
enter cell cycle.
G0 Phase :- Some cells in the adult animals do not appear to
exhibit division (e.g.,heart cells) and many other cells divide only
occasionally, as needed to replace cells that have been lost because of
injury or cell death. These cells that do not divide further exit G1 phase
to enter an inactive stage called quiescent stage (G0) of the cell cycle.

11. (ii) S Phase :- ◆ Also called synthasis phase.
◆ During this stage the amount of DNA per cell doubles. If the initial
amount of DNA is denoted as 2C then it increases to 4C. However
there is no increase in the chromosome number.
◆ Also synthesis of basic nulcear protein The Histone.
(iii) G2 Phase :- ◆ Also called gap 2 or growth 2 phase.
◆During this phase proteins are synthesised in preparation for
mitosis while cell growth continues.
◆ Also termed as pre-mitotic phase.

12. (B) M Phase :- ◆ The M Phase represents the phase when the
actual cell division or mitosis occurs.
◆ The M Phase starts with the nuclear division, corresponding to the
separation of daughter chromosomes (karyokinesis) and usually end
with division of cytoplasm (cytokinesis).
◆ It is active stage of cell cycle it takes only 1hour to complete.
MITOSIS DIVISION
The mitosis division has following sub phases :- (I)Karoyokinasis
(A) Prophase :- ◆ Condantation of chromatides.
◆ Disappear of nuclear envalope.

13. ◆ disappear of nucleolus.
◆ Activation of MTOC and formation of
of spindal fiber.
◆ Centromere started to move to
opposite pole.
(B) Metaphase :- ◆ Spindal fiber
formation complete.
◆ Centromere completely move to
opposite pole.
◆ Nuclear envalope completely disappear.

14. (C) Anaphase :- ◆ Homoloogus chromosome
seprate and move to opposite pole.
◆ Centromeres split and chromatids separate.
◆ Chromatids move to opposite poles.
(D) Telophase :- ◆ Nucleus envalope
Re-form.
◆Cleavage farma formation.
◆ Nucleolus, golgi complex and ER reform.

15. (II) Cytokinasis :- ◆ Division of cytoplasm.
◆ End of this phase 2 daughter cell forms.
◆ Construction of Actine and Myocine
Form 2 cell.
Significance of Mitosis :-
◆ Equal destribution of chromosome.
◆ In this division every mother cell form
two daughter cell.
◆ Repairing.

18. MIOSIS DIVISION
1. Miosis I :- (A) Prophase I
(i) Leptotene :- ◆ Condantation of
chromosome.
◆ Disappear of nucleus envalope.
◆ Disappear of nucleolus.
(ii) Zygotene :- ◆ Pairing of homologus
chromosome, it is called synapsis.
◆

19. (iii) Pachytene:-
Crossing over :- Crossing over is
process of exchanging genetic matterial
between non-sister chromatids of
homologous chromosome.
(iv) Diplotene :- ◆ Appearing of
chrossing over in this stage.
◆ Lymbrush chromosome appearing
on diplotene stage.

20. (v) Dikinesis :- ◆ Chromosome condanced
and nuclear envalope fragmented and spindal
fiber formation.
◆ RNA synthesis ceased.
(B)Metaphase I :- ◆ Condantation of
chromatides.
◆ Spindle fiber completely form.
◆ Centromere move to equater pole.

21. (C) Anaphase I :- ◆Separation of homologous
chromosome.
(D) Telophase I :- ◆ Nucleus membrane
reform.
◆ Kinatofore and spindle fiber disole.
◆ Cleavage farma form.
2. Miosis II :-
(A) Prophase II :- ◆ Condantation of chromatids.
◆ Disappear of nucleus envalope.

22. ◆ Disappear of nucleolus.
◆ Centriole move to opposite poles.
◆ Formation of spindle fiber.
(B) Metaphase II :- ◆ Spindle fiber
completely form
◆ Condanced chromatids.
(C) Anaphase II :- ◆ Homologous chromo-
Some moved opposite pole.
◆ Separation of sister chromatids.
(D) Telophase II :- ◆ Nucleus envalope reform.
◆ Spindle fiber disole.

23. ◆ After this phase complete 4 cell form.
Significance of Miosis
◆ The meiosis maintains a definite and constant number of
chromosome in the organism.
◆ By crossing over, the meiosis provides an opportunity for the
exchang of the gene and thus cause the genetical variations amoung
the species. The variation are the raw matterial for the evolutionary
process.

25. 4. Difference between mitosis & miosis :-

26. 5. Cell cycle control system :- Rapid or uncontrolled cell division
can cause cancer and lack of cell division cause undevelopement of cell
organells, so cell division is very important.
For understanding how cell cycle is
control we need to know 3 things :-
1. Possitive signal :- For division – Cyclin / Cdk
2. Negetive signal :- To stop division – P53, P21, ATM, ATK
3. Time point also called checkpoint when the cell divide or stop
division.
◆ The sequincial events of the cell cycle are directed by a distinct “ cell
cycle control system” which is similar to a clock.
◆ The control of essential process of the cell cycle such as – DNA
replication , mitosis, and cytokinasis are triggered by cell cycle control
system.

27. ◆ The cell cycle control system is regulated at certain checkpoints.
◆ At each checkpoints the cell decided if it should go on with division.
6. Triggers the major process of cell cycle :- The cell cycle
control system operates much like the control system of an automatic
clothes- washing machine. The washing machine functions in a series
of stages : it takes in water, mixes it with detergent, washes clothes,
rinses them and spin them dry. These essential process of the wash
cycle analogous to the essential processes of the cell cycle – DNA
replication, mitosis and so on. In both case a central controller triggers
each process in a set sequence.
◆ A clock or timer that turns on each event at a specific time, thus
providing a fixed amount of time for the completion of each events.

28. ◆ A machanism for initiating events in the correct order; entry into
mitosis, for example, must always come after DNA replication.
◆ A machanism to ensure that each events is triggered only once per
cycle.
◆ Binary(on/off) switches that triggers events in a complete,
irreversible fashion.
◆ Robustness: backup machanisms to ensure that the cycle can work
properly even when parts of the system malfunction(imperfectly
function)
◆ Adaptibility so that the system’s behaviour can be modified to suit
specific cell types or environmental condision.

29. 7. Cell cycle checkpoints :- ◆ Checkpoints play very important
role in the cell cycle.
◆Checkpoints ensure that the cell are ready to proceed through the
process of division.
◆ At each checkpoints the cell waits to recieve signals that whether
division or not.
◆ If the cell recieve the correct signal it will allow itself to continue
through the cell cycle if not then stop cell cycle completely.
There are 3 checkpoints in the cell cycle:
1. G1 Checkpoint :- ◆ Also called G1-S checkpoint.
◆ It checks that a cell have enough nucleotide to duplicate DNA or not,
if the have not enough nucleotide then the cell will arrest and stop
dividing.

30. ◆ If the cell recieve signal to not dividing then cell stop dividing just
before G1 checkpoint.
2. G2 Checkpoint :- ◆When the cell pases G1 checkpoint it enter S-
phase.
◆ Also called S-G2 or G2-M checkpoint.
◆ At G2 checkpoint the cell checks following things: firstly it check
DNA for any damage that might occured during replication.
◆ It also ensure that all the proteins needed for cell division are
present or not.
◆ It also ensure that DNA replication properly happened ?
◆ Once the cell pases the G2 checkpoint enter in mitosis or miosis.

31. 3. M Checkpoint :- ◆ The last checkpoint, the M checkpoint happens
at end of metaphase.
◆ To pass this checkpoint the cell must have all sister chromatids
attached to spindle.
◆ The checkpoint ensure that chromosome proparly separate during
anaphase.
◆ This checkpoint ensure that the 2 cell produced by mitosis or miosis
division with the correct number of chromosome.
◆ This is important because incorrect number of chromosome can
cause various disease.

34. 8. The regulation of cell cycle:- The regulation of cell cycle
depends on cyclin and cdk.
◆ Cyclin :- Cyclin are the protein, which is always secreted inside the
cell in small amount. Cyclin is speciefic for each phase.
Example: G1-S cyclin will not function at G2- m-phase cyclin & M-phase
cyclin will not function at G2-S- phase cyclin because they are specific
for the specific phase of the cell cycle & cell progress to the next level.
◆ Cdk :- Cdk is cyclin dependent kinase, so the activation of this
depends on cyclin.If there is no cyclin, Cdk will not activate and not
functioning. Cdk is present in the cell always, depend on cyclin to
activate.

35. Mainly 3 types of complex found on the cell cycle:-
1. G1-S cyclin + Cdk complex (Cyclin E)
2. S-G2 cyclin + Cdk complex (Cyclin A)
3. M cyclin + Cdk complex (Cyclin M)
1. G1-S Cyclin + Cdk complex :- Cdk and G1-S cyclin will pair each
other and they become activated & they phosphorylate some target
proteins.
(Inactivate) Cdk + Cyclin
|
(Active) Cdk-Cyclin complex
|

36. |
Phosphorylate other protein
And other two complexes Cdk-SG2 cyclin complex and Cdk-M cyclin
complex works same as G1-S cyclin-Cdk complex that cyclin attach with
Cdk and activate the Cdk and they works.
How Cdk-cyclin pattern works?
A Cdk is not active because it is not bounded with cyclin. Then the M
cyclin and Cdk pair and phosphorylate Cdk.
Here is one thing:- When Cdk bimd to cyclin then it is not completly
activare. Now it required other proteins(two different type of kimase
involve)
1. V1 :- Inhibitory kinase
2. Cak :- Activatory kinase

39. 9. Conclusion :- The cell cycle complete in two phase – interphase
with following sub-phases - G1, S, G2 and M-phase – mitosis and
miosis. The cycle have some checkpoints also they control the cycle by
dividing futher or not and cell cycle is regulated by cyclin and Cdk.
The cell cycle is very important in
animals because of growth and cell cycle regulation is also very
important because the rapid or uncontrol cell division can cause cancer,
and lack of cell division can cause undeveloped cell organells.
10. Refrence :- ◆ The cell :- Albert Bruce
◆ Cell & molecular biology :- Gerald Karp
◆ Singh & Tomar
◆ Internet