Centrosomes, Kinetochores. Chromosome segregation II

Question 1

What is the microtubule-organising centre

Answer 1

• called a centrosome in animal cells
• spindle pole body in yeast
• two centrioles organise the centrosome matrix, forming a centrosome
• gamma-tubulin complex gives nucleation sites of MTs
• MTs extend from MTOCs with the distal plus end

Question 2

Structure of the y-tubulin complex

Answer 2

• 7 copies of y-tubulin small complexes are arranged in a spiral
• provides template for MT nucleation

Question 3

Structure of centriole

Answer 3

• 9-fold symmetry
• triplets of short MTs are arranged around the cartwheel structure

Question 4

S/G2 centrosome duplication

Answer 4

• stimulated by S-CDK
• mother centriole promotes elongation of a daughter centriole

Question 5

Early prophase centrosome duplication

Answer 5

• aster formation
• centrosome separation

Question 6

Late prophase-prometaphase centrosome duplicaiton

Answer 6

mitotic spindle is formed between two centrosomes

Question 7

How do microtubules attach to chromosomes

Answer 7

• MT plus end attaches at the Kinetochore
• Kinetochore has a plate-like structure
• each chromatid has only one kinetochore

Question 8

Kinetochore attachment in metaphase

Answer 8

single kinetochore attaches to a single MT in budding yeast, whereas single kinetochore attaches to 20-30 MTs in humans

Question 9

Structure of centromeres in EU cells

Answer 9

• chromosome regions supporting kinetochore assembly
• structure varies among organisms but CENP-A nucleosomes are commonly found
• point centromeres in budding yeast are defined by consensus DNA sequence
• regional centromeres in others are maintained by CENP-A-dependent epigenetic mechanisms

Question 10

Where are centromeres in vertebrate cells

Answer 10

embedded in heterochromatin

Question 11

Structure of kinetochore in budding yeast

Question 12

Structure of kinetochore in humans

Question 13

Process of kinetochore-MT interaction

Answer 13

1. Kinetochore capture by lateral surface of MT (lateral attachment) (pro-meta)
2. MT-dependent kinetochore transport towards a spindle pole (end-on attachment) (pro-meta)
3. Both sister kinetochores interact with MTs from the same or opposite spindle poles (pro-meta)
4. Sister kinetochore bi-oientation (metaphase)

Question 14

How is lateral attachment converted to end-on attachment

Question 15

Key molecules in budding yeast

Answer 15

• Ndc80 complex: direct MT attachment
• Dam1 complex: tethers kinetochore at the MT end

Question 16

Errors in chromosome bi-orientation during chromosome segregation

Answer 16

• can lead to merotelic attachment
• threat for dividing cells as it occurs in early mitosis
• can lead to chromosome mis-segregation and aneuploidy

Question 17

Define monotelic attachment

Answer 17

(mono-orientation) when one single pole and kintochore-microtubule is attached to the chromosome, occurs before metaphase

Question 18

Define amphitelic attachment

Answer 18

(bi-orientation) when two spindle poles and kintochore-microtubule are attached to the chromosome during metaphase

Question 19

Define syntelic attachment

Answer 19

(mono-orientation) when a spindle pole binds two sister kinetochore-microtubules of the singular chromosome

Question 20

Define merotelic attachment

Answer 20

error occurring when a single kinetochore is attached to microtubules emanating from both spindle poles

Question 20

Define merotelic attachment

Answer 20

error occurring when a single kinetochore is attached to microtubules emanating from both spindle poles

Question 21

Role of Aurora-B kinase in error correction

Answer 21

• phosphorylates Dam1 which weakens association with Ndc80C
• disrupts end-on attachment
• promotes exchange to new MT lateral attachment
• establishes bi-orientation
• kinetochores delocalise from aurora B
• kinetochore components are dephosphorylated
• kinetochore-microtubule is established
• tension is generated by cohesin