Centromeres

Question 1

Are the following statements true or false?

A: Centromeres are highly heterochromatic.
B: Centromeres aren’t wrapped around histones.

Answer 1

A: TRUE.
B: False. The centromere is highly condensed, it’s wrapped around Cse4 (an H3 analogue) and H4.

Question 2

Describe the kinetochore structure.

Answer 2

1. Trilaminar
2. Highly conserved.

Question 3

Describe the centromere structure.

Answer 3

1. Simple organisms have shorter centromere sequences. Mammalian centromere length = 240 kb.
2. Centromere center is AT-rich.
3. Not conserved! (Unlike the centromeres)

Question 4

What’s the CEN-DNA paradox?

Answer 4

It states that kinetochores are conserved while the centromeres aren’t.

Question 5

Which of the three kinetochore laminas is the most conserved? Why is this?

Answer 5

The two innermost laminae. The outermost lamia is the most conserved.

The inner laminas of the kinetochore are referred to as CCAN (constitutive centromere-associated network). Since these laminae interact with the DNA, they evolve with them.

Question 6

A: Which three proteins of the innermost kinetochore lamina are the most important?

B: Which two proteins of the two outer layers are the most important?

Answer 6

A
CENP-A: H3 analog.
CENP-B: Binds DNA (alpha satellite repeats)
CENP-C: Recruits CENP-A.

B
CENP-D
CENP-E

Question 7

What’s the complex that binds centromere and kinetochore together called? What’s the consequence of failed centromere-kinetochore interactions?

Answer 7

NDC80.

If the kinetochore-centromere interaction fails, the organelles/chromatids won’t be separated properly, this leads to aneuploidy/organelle deficiency.

Question 8

Correct the following statement:

The kinetochore needs to be non-phosphorylated before interacting with the centromere.

Answer 8

The kinetochore is phosphorylated when binding to the centromere. When it’s bound, the phosphorylations are removed. If the kinetochore gets phosphorylated during its interaction with the centromere, they dissociate.

If a single kinetochore-centromere interaction fails, MAD2 mediates an anaphase pause. (MAD2 inhibits c-MYCs cell cycle progression effect).

Question 9

Before segregation, the chromatids are bound to each other via cohesins. How are these interactions disbanded?

Answer 9

APCU cleaves the securin-separase complex which frees separase that in turn degrades the cohesins.

Question 10

How do you generate a YAC (Yeast artificial chromosome)?

Answer 10

1. Transform circular YAC into e.coli in order to amplify it.
2. Transfect circular YAC into yeast.
3. Insert telomerator cassette into the YAC in order to provide stability.
4. Grow on selection plates.