Regulation of gene expression

Question 1

Describe the different ways gene expression can be regulated [4]

Answer 1

At transcription - degradation of hnRNA
At translation - degradation of mRNA / sequestering of mRNA into inactive form (reactivated when certain signals arise)
Degradation of polypeptide before it becomes a functional protein

Question 2

Describe the two mechanisms by which transcription is controlled

Answer 2

Binding of sequence specific TFs to DNA
Control of DNA packaging

Question 3

What are cis-acting sequences

Answer 3

DNA sequences found within the promoter
Some may be near the transcription start site , others may be significantly further away
They bind to TFs to help regulate gene transcription

Question 4

TFs have 2 binding sites : name them

Answer 4

DNA-binding site and RNA-polymerase binding site

Question 5

How do TF up to 100kb from the transcription start site regulate transcription ?

Answer 5

A mediator protein with several domains binds many TFs, RNA polymerase and other gene regulatory proteins together all at once , creating a protein complex and causing the DNA to loop

Question 6

Many TFs bind to DNA

true or false ?

Answer 6

False

many TFs do not bind to DNA

Question 7

DNA-binding TFs recruit essential regulators called :

Answer 7

Co-activators

co-repressors

Question 8

What are histones

Answer 8

Small basic proteins containing many C-terminal lysines

Question 9

Describe the action of co-activators

Answer 9

They open chromatin structure in 3 ways :

1. histone acetyltransferases (more acetylation = less condensed)
2. recruiting a chromatin remodelling complex which can remodel the nucleosome
3. chromatin remodelling complex may also recruit histone chaperone to remove histones or modify the histones present

Question 10

Describe the action of co-repressors

Answer 10

They work by closing up the chromatin structure

Histone deacetylases

histone methyl transferases.

Question 11

What are the different ways transcription regulator activity is modulated ?

Answer 11

Ligand binding

covalent modification

addition of a second subunit

unmasking

stimulation of exit from the nucleus

release from membrane

Question 12

What is p53?

Answer 12

A TF responsible for activating mutiple genes involved in cell cycle arrest , DNA repair and apoptosis

mutations of p53 are responsible for 50% of human cancers

Question 13

De-adenylation of mRNA leads to its

Answer 13

Degradation