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Flashcards in Chromosome segregation Deck (35):
1

How long does mitosis take

About an hour

2

What happens to the chromosomes during mitosis

They are segregated

3

Why is proper chromosome segregation important

Essential for cell proliferation and to avoid an abnormal number of chromosomes in a cell

4

What does aneuploidy mean

An abnormal number of chromosomes

5

What can happen is chromosomes are missegregated

Diseases.
Somatic cells -> cancer
Development -> Downs syndrome

6

How can chromosome missegregation lead to cancer

A cell may have two types of tumour suppressor gene (1 active/ 1 inactive). If a cell missegregates and doesnt have an active tumour suppressor gene -> cancer

7

What are the stages of a cell cycle

Interphase (G1, S, G2)
Prophase
Prometaphase
Metaphase
Anaphase
Telophase

8

What happens in interphase

Chromosomes and centrosomes duplicate

9

What happens in prophase

Chromosomes start to condense. Centrosomes separate and form asters

10

What happens in prometaphase

Nuclear envelope broken down, microtubules interact with chromosomes

11

What happens in metaphase

Chromosomes bi-orient on spindle and align on the metaphase plate

12

What happens in anaphase

Sister chromatids separate and move towards spindle poles. Spindle poles move apart

13

What happens in telophase

Chromosomes arrive as poles and decondense. Nuclear envelope reassembles.

14

What factors promote mitosis initiation

M-phase cyclin/CDK complex

15

How are M-phase cyclin/CDK complexes regulated

(de)phosphorylation of CDKs
Proteolysis of M-phase cyclins

16

What effect does phosphorylation have on CDKs

Inactive when phosphorylated.
Wee1 -> CDK-inhibitory kinase.
CDC25 -> phosphatase that is activated by the M-phase cyclin/CDK complex. Removed a phosphate and activates CDK.

17

How are M-phase cyclins regulated

APC/C (anaphase-promoting complex/cyclosome) is activated by forming a complex with CDC20 or CDH1. When active it can target M-cyclin for ubiquitin degradations

18

How do chromosomes become prepared for mitosis

Sister chromatid cohesion established by cohesin complex
Chromosomes are condensed (prophase)

19

Why is the cohesin complex important

Establishes cohesion of sister chromatids.
Enables chromosome bi-orientation, and allows the cell to know which sisters to segregate

20

What subunits are present in the cohesin complex

SMC1/3
SCC1/3

21

How is the mitotic spindle formed

Astral MTs radiate from centrosomes and orient the spindle
Kinetochore MTs attach to kinetochores and regulate chromosome motion
Interpolar (polar) MTs inter-digitate at spindle equator and generate force to separate the poles.

22

How can the length of a microtubule vary

Stabilisation of MT = longer MTs
Destabilisation of MT = shorter MTs

23

How is chromosome motion regulated during meta/ana phase

(De)Polymerisations of kinetochore MTs.

24

When and how are centrosomes duplicated

During S/G2-phase.
Stimulated by S-CDK

25

What is the role of Aurora-B kinase

Important for error correction in mitosis.
If the sister chromatids are not separated correctly, then the MT components are phosphorylated (by Aurora-B kinase)and cannot separate the chromatids.
When the right tension is applied, Aurora B is inactivated/delocalised. MT components are dephosphorylated and the chromatids can separate

26

What is a syntelic attachment

Mono-orientation of the MTs. No tension. Chromatids cannot separate

27

What is an amphitelic attachment

Bi-orientation of the MTs. Tension. Chromatids can separate

28

How do sister chromatids separate in anaphase

Separase usually inactive (by securin). Active ACP/C is able to ubiquitinate securin and signal for degradation.
Active separase breaks the bond between SCC1/3 in the cohesin complex. Chromatids are free to separate.

29

How do chromosomes move in anaphase A

Kinetochore MTs shorten due to MT flux and depolymerisation at + end.
Movement towards the poles.

30

How do chromosomes move in anaphase B

Move away. Slide between interpolar MTs. Poles pulled towards cell cortex.
Movement towards the poles

31

Name some checkpoints in the cell cycle

G1/S - monitors cell size and DNA damage
G2/M - monitors DNA replication completion and DNA damage
Spindle assembly checkpoint - monitors kinetochore-MT attachment.

32

When does the spindle assembly checkpoint occur

Between metaphase and anaphase.
Prevents anaphase onset.
Important because anaphase is irreversible.

33

What does the spindle assembly checkpoint consist of

Sensors (kinetochore components)
Mediators (MAD/BUB proteins)
Effectors (anaphase-promoting complex; APC)

34

How is cytokinesis regulated

Triggered by loss of M-CDK activity
Central spindle stabilises cell separation.
Both mechanisms ensure cytokinesis only occurs after chromosome segregation

35

How is meiosis different to mitosis

Mitosis = DNA replication; Chromosome segregation. Repeat.
Meiosis = DNA replication; 2 rounds of chromosome segregation. Repeat. (facilitated by second anaphase)