mitosis and meoisis

Question 1

What are the essential events of mitosis?

Answer 1

1. Chromosome structure changes (condensation and decondensation).
2. Bipolar spindle assembly.
3. Bi-orientation of chromosomes on the spindle.
4. Separation of sister chromatids (anaphase).
5. Cytokinesis - cell division into two daughters.

Question 2

What regulates mitotic entry?

Answer 2

M-Cdk (Cyclin B-Cdk1), which:

Directly phosphorylates key substrates.
Activates downstream mitotic kinases like Aurora and Polo.

Question 3

What happens during prophase?

Answer 3

1. Chromosomes condense (Cohesin lost, Condensins recruited).
2. Kinetochore assembly begins.
3. Centrosomes move apart, and spindle starts forming.

Question 4

What is the kinetochore?

Answer 4

The kinetochore is a macromolecular complex that assembles on the centromere. It serves as the microtubule binding site for chromosome movement during mitosis.

Question 5

What changes occur during prometaphase?

Answer 5

1. Nuclear envelope breaks down.
2. Microtubules bind to kinetochores.
3. Error correction ensures proper microtubule attachment.

Question 6

What is the spindle checkpoint?

Answer 6

A surveillance mechanism ensuring all chromosomes are bi-oriented. Unattached kinetochores produce the Mitotic Checkpoint Complex (MCC), which inhibits APC/C to prevent progression.

Question 7

What happens during metaphase?

Answer 7

1. Chromosomes align at the metaphase plate.
2. All chromosomes are bi-oriented.
3. Spindle checkpoint is silenced, and APC/C is activated.

Question 8

What role does APC/C play in mitosis?

Answer 8

1. APC/C degrades M-Cyclin and Securin.
2. This triggers “biochemical” mitotic exit and anaphase onset.
3. Separase cleaves cohesins to separate sister chromatids.

Question 9

What are the key events in anaphase?

Answer 9

Anaphase A: Chromosomes move to spindle poles.
Anaphase B: Spindle poles move apart (microtubule motors like kinesin-5 drive this).

Question 10

What occurs during telophase?

Answer 10

Chromosomes decondense (Condensins dissociate, Cohesins re-associate).
Nuclear envelope reforms.
Interphase chromosome structure is re-established.

Question 11

What is cytokinesis?

Answer 11

A contractile ring of actin and myosin forms the cleavage furrow.
The dividing cell is pinched into two daughter cells.

Question 12

What is bi-orientation, and why is it important?

Answer 12

Bi-orientation occurs when each sister chromatid is attached to opposite spindle poles. It ensures accurate segregation of chromosomes.

Question 13

How does Aurora B kinase contribute to error correction?

Answer 13

Detects tension at the centromeres.
Phosphorylates Ndc80, releasing improperly attached microtubules from kinetochores.

Question 14

What are the major stages of mitosis in summary?

Answer 14

Prophase: Chromosomes condense, spindle begins to form.
**Prometaphase: **Nuclear envelope breaks down, microtubules attach to kinetochores.
Metaphase: Chromosomes align at the metaphase plate.
**Anaphase: **Chromosomes move to poles.
Telophase: Chromosomes decondense, nuclear envelope reforms.
Cytokinesis: Cell divides into two.

Question 15

What are the components of a mitotic spindle?

Answer 15

Kinetochore microtubules: Attach to chromosomes.
Interpolar microtubules: Stabilize the spindle.
Astral microtubules: Anchor spindle poles