Nov 6

Question 1

How is the mating type controlled in yeast, give a basic idea. What endosome and what stage of cell cycle? How is the endosome transcribed?

Answer 1

The Mat locus has either the a or alpha gene in it. Diplod has 2 Mat locuses of course so it has 1 of each. The HO endosome in maternal cells in the G1-S stage causes ds break to cause the gene to enter Mat locus.

First SWI5 binds which recruits lots of histone deacetylase and chromatin remodelling complex, so now SBF site available for SBF to bind, now get HO expression

Question 2

What is bound and not bound for each mating type of yeast?

Answer 2

For a cell, have Mcm1 (regulator) turning on a-specific genes. Alpha celll has McM1 binding but alpha 2 repressor binds as well. Then Can also have a1 in diplod that combines with the a2 repressor to turn off haploid specific genes.

Question 3

What are the 4 ways transcription repressors work?

Answer 3

1. They bind to promotor so RNA pol can’t bind
2. Interact with RNA Pol to inhibit function
3. Interfere with activators
4. Recruit histone modifiers to make chromatin more compact

Question 4

Describe Jak/Stat pathway in basic.

Answer 4

The receptor subunits dimerize and PO4 each other.
2. Two Stat monomers dimerize, and bind to PO4 Tyr with the SH@ domain, then go into nucleus and act as transcription factor

Question 5

How are genes extra silenced at telomeres and centromeres?

Answer 5

1. Has Rap1 bind to DNA and recruit silence information regulator (SIR) proteins.
   Sir 2 will deacetylate histones, then Sir 3 and 4 will extend this effect to govern ore area. Forms heterochromatin which is very compact

Question 6

What does methylation of cytosines in CpG islands do?

Answer 6

It prevents transcription of the gene, but some can occur. Then if proteins bind to methylated DNA, and recruit deacetylases and remodelling complexes, then the gene becomes completely off

Question 7

What is imprinting of parental methylation?

Answer 7

It has parental strand with methlation so the imprinting control region does not have insulator on it, so the enhance can activate the Igf2 and promotes cell division.

For maternal chromosome, no methylation so ICR has insulator on it, it blocks signal and also activates another gene as a result, so suppress cell division.

Question 8

How is DNA methylation passed on?

Answer 8

As DNA replication is semi-conservative, the maintenance methylase recognizes hemimethylated and methylates the other strand