Lecture 13: Metaphase and anaphase

Question 1

What can occur and block the transition of metaphase to anaphase?

Answer 1

Microtubules depolymerise
Microtubules stabilised
Spindle not assembled properly
A kinetochore isn’t attached to the spindle

Question 2

What happens if the chromosomes are unaligned and the kinetochores are unattached in metaphase?

Answer 2

Stop signal generated by spindle assembly checkpoint complex at the kinetochore
Anaphase is delayed

Question 3

What happens if the chromosomes are aligned and the kinetochores are attached in metaphase?

Answer 3

Spindle assembly checkpoint proteins are removed from kinetochores by cytoplasmic dynein and anaphase continues

Question 4

What happens if a cell enters anaphase too early?

Answer 4

Aneuploid daughter cells will the wrong number of chromsomes

Question 5

What is different about M-Cdk in metaphase and anaphase?

Answer 5

Active in metaphase
Inactive in anaphase

Question 6

What is different about cohensins in metaphase and anaphase?

Answer 6

In metaphase sister chromatids are held together by cohensins
In anaphase they come apart as cohensins are cleaved

Question 7

How does the transition from metaphase to anaphase happen?

Answer 7

1. Chromosomes align and spindle assembly checkpoint is off
2. Anaphase promoting checkpoint is on
3. Separase is activated

Question 8

What is the role of the anaphase promoting complex?

Answer 8

Trigger proteolysis of certain proteins
1. Covalently attaches ubiquitin
2. This tags the proteins and directs them to a proteasome for degradation

Question 9

What are the key substrates tagged by ubiquitin?

Answer 9

Cyclin B subunit of M-Cdk
Securin

Question 10

What occurs in anaphase A?

Answer 10

Sister chromatids move towards the spindle poles

Question 11

What occurs in anaphase B?

Answer 11

Spindle poles move further apart

Question 12

How do the spindle poles move apart in anaphase?

Answer 12

1. Kinesin Eg5 crosslinks antiparallel microtubules and pushes the centrosomes apart
2. Interpolar microtubules continue growing
3. Dynein at cell cortex pulls on astral microtubules

Question 13

What occurs during telophase?

Answer 13

Genome is equally separated
Nuclear envelope and nuclear lamins reassemble
Golgi apparatus reassembles
Secretion and endocytosis restart

Question 14

What is the main role of cytokinesis?

Answer 14

Divide the cytoplasm

Question 15

How does cytokinesis occur in animal cells?

Answer 15

1. Central spindle recruits and activates proteins
2. Proteins signal to cortex to start contractile ring assembly
3. Contractile ring gets smaller over time

Question 16

In what ways does the morphology of animal cells change?

Answer 16

Cells can become rounded and less well attached to surface
Actin and myosin filaments are rearranged
Integrins are phosphorylated and weaken grip on extracellular matric

Question 17

How is cell division different in plant cells?

Answer 17

No centrosomes or dynein
Spindle poles are broad and organised by minus end kinesins

Question 18

How does telophase and cytokinesis occur in plant cells?

Answer 18

Make a new cell membrane then wall
This required golgi derived vesicles and microtubules