Mitosis

Question 1

What is the cell cycle ?

Answer 1

The series of events that a cell goes through to grow, replicate its DNA and divide into 2 daughter cells

Question 2

What are the phases of the cell cycle ?

Answer 2

1. Gap phase 1 (G1)- cell grows in size
2. Synthesis phase (S)- DNA replication occurs
3. Gap phase 2 (G2)- further growth
4. Mitotic phase (M)- where mitosis takes place

Question 3

What are the stages of mitosis ?

Answer 3

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 4

Describe interphase

Answer 4

1. DNA unravells
2. DNA is replicated
   Interphase consists of G1, S and G2 phases

Question 5

Describe prophase

Answer 5

1. Chromosomes condense
2. Mitotic spindle forms
3. Nuclear envelope breaks down

Question 6

Describe metaphase

Answer 6

1. Chromosomes align at the centre
2. Spindle fibres attach to the centromere of each chromosome

Question 7

Describe anaphase

Answer 7

1. Spindle contracts, pulling sister chromatids to opposite ends of the cell

Question 8

Describe telophase

Answer 8

1. Nuclear envelope forms
2. Spindle fibres degrade
   Now called chromosomes again

Question 9

Describe cytokinesis

Answer 9

1. Cytoplasm divides, resulting in 2 genetically identical daughter cells

Question 10

What holds the chromatids together ?

Answer 10

Cohesin proteins wrap around the centromere forming a dimer loop, which keeps them together

Question 11

How do the chromosomes condense ?

Answer 11

Condensin use ATP to loop the chromatin and fold into compact structures

Question 12

How do the chromosomes attach to the spindle ?

Answer 12

1. Astral micro tubules extend out from the centrosomes and bind to the plasma membrane to keep the spindles fixed in place using Dynein.
2. Kinetichores attach the spindle fibres to the chromosomes.
3. Motor proteins (Kinesin and dynein) adjust the tension of the fibres to align the chromosomes.
   The Mitotic spindle is made of microtubules that are composed of protein filaments called tubulin.

Question 13

Role of Kinesin-14

Answer 13

Tightens the spindle

Question 14

Role of kinesin-5

Answer 14

Expands the spindle

Question 15

What orientates the chromosomes ?

Answer 15

The kinetichore and kinesins

Question 16

What pulls the chromatids apart ?

Answer 16

1. Anaphase-promoting complex marks securin for degration
2. Separase is activated and cleaves cohesin, which mean that the sister chromatids are no longer held together
3. Kinetochore microtubules shorten, pulling chromatids to opposite poles of the cell