Cyclins regulate the cell cycle by binding and activating cyclin-dependent kinases (CDKs). There are different cyclins that correspond to each stage of the cell cycle - G1, S, G2, and M phases. Cyclins have no enzymatic function themselves but bind to CDKs to form complexes that phosphorylate target proteins and control progression through the cell cycle checkpoints. Cyclins associate with specific CDKs to drive the cell cycle forward at each stage.

1. Medical Cell Biology
Home Work

2. What is the main difference between
Mitosis and Meiosis :-
Mitosis
• In Mitotic division, a single division results in two
daughter cells.
• Mitosis is known as equational division. This is
because the daughter cells have the same diploid
number of chromosomes as the parent.
Meiosis
• Meiotic division involves two successive divisions
meiosis I and meiosis II. These divisions result in
four daughter cells.
• Meiosis I is known as reductional division. This is
because the chromosome number is reduced to
half. Meiosis II is known as equational division.
This is because the sister chromatids separate and
the chromosome number remains the same.

3. Mitosis Meiosis
• Prophase is short and does not
comprise any phase.
• There is no pairing of chromosomes,
crossing-over, or chiasmata-formation
during prophase.
• Prophase I is very long and comprises
5 phases –leptotene, zygotene,
pachytene, diplotene, and diakinesis.
• In the zygotene stage of prophase, the
pairing of chromosomes occurs.
During pachytene, the crossing-over
occurs. The chiasmata are formed in
the diplotene stage.

4. Mitosis Meiosis
• Synaptonemal complex is not formed.
• Anaphase involves the separation of
the chromatids of each chromosome.
• Synaptonemal complex is formed
during the zygotene stage of prophase
I.
• During anaphase I, the homologous
chromosomes separate, while the
chromatids remain attached at their
centromeres.
• During anaphase II, the chromatids
separate as a result of the splitting of
the centromere.

5. Mitosis Meiosis
• Number of chromosomes remains
the same.
• Homologous chromosome do not
pair up.
• Chiasmata do not form and crossing
over never occurs.
• Daughter cells are genetically
identical.
• Two divisions Number of chromosomes is
halved.
• Homologous chromosome pairup to form
bivalent
• Chiasmata form and crossingover Occurs
• Daughter cells are genetically different from
the parent cells.

7. 2.What is the main function of Cyclin:
• The cell cycle is regulated by cyclins, a type of protein that binds and
activates cyclin dependent kinases (CDKs).
• The accurate transmission of genetic information from a cell to a daughter
cell is ensured by the tight regulation of the four stages of the cell cycle. The
stages of this cycle include: Gap 1 (G1) phase, DNA synthesis (S) phase, gap
2 (G2) phase, and mitosis (M) phase. For each phase, there is a
corresponding group of cyclins: G1 cyclins, G1/S cyclins, S cyclins and M
cyclins, each with a different function.

8. Function of cyclins in the cell cycle:
• Cyclins have no enzymatic function of their own, and instead bind to CDKs
to activate them. Once bound, they form maturation promoting factors
which can phosphorylate target proteins and lead to the many different
stages of the cell cycle.
• Cyclins are the regulatory subunits of holoenzyme CDK complexes that
control progression through cell-cycle checkpoints by phosphorylating and
inactivating target substrates. The cyclins associate with different CDKs to
provide specificity of function at different times during the cell cycle.