Lecture 13: Metaphase and anaphase Flashcards

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1
Q

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

A

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

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2
Q

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

A

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

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3
Q

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

A

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

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4
Q

What happens if a cell enters anaphase too early?

A

Aneuploid daughter cells will the wrong number of chromsomes

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5
Q

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

A

Active in metaphase
Inactive in anaphase

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6
Q

What is different about cohensins in metaphase and anaphase?

A

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

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7
Q

How does the transition from metaphase to anaphase happen?

A
  1. Chromosomes align and spindle assembly checkpoint is off
  2. Anaphase promoting checkpoint is on
  3. Separase is activated
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8
Q

What is the role of the anaphase promoting complex?

A

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

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9
Q

What are the key substrates tagged by ubiquitin?

A

Cyclin B subunit of M-Cdk
Securin

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10
Q

What occurs in anaphase A?

A

Sister chromatids move towards the spindle poles

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11
Q

What occurs in anaphase B?

A

Spindle poles move further apart

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12
Q

How do the spindle poles move apart in anaphase?

A
  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
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13
Q

What occurs during telophase?

A

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

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14
Q

What is the main role of cytokinesis?

A

Divide the cytoplasm

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15
Q

How does cytokinesis occur in animal cells?

A
  1. Central spindle recruits and activates proteins
  2. Proteins signal to cortex to start contractile ring assembly
  3. Contractile ring gets smaller over time
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16
Q

In what ways does the morphology of animal cells change?

A

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

17
Q

How is cell division different in plant cells?

A

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

18
Q

How does telophase and cytokinesis occur in plant cells?

A

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