6. Gene Regulation and Epigenetics

Question 1

What are the 3 main differences as to why different types of cells share same genome but look & function different?

Answer 1

1. Heterochromatin vs. Euchromatin
2. Presence or absence of specific transcription factors
3. Splicing

Question 2

Histone Modification Complexes (HMC)

Answer 2

Modify histone tails in nucleosome to increase or decrease their affinity to DNA.
1. Methylation
2. Acetylation

Question 3

Histone Tails

Answer 3

Highly abundant in positively charged lysine residues that ATTRACT DNA.
* Positively charged tails interact with Negatively charged phosphates of DNA

Question 4

Acetylation - Relaxes DNA

Answer 4

Acetylation of lysines changes histone tail (+) charge to (-) charge
* Reduces affinity of histone tails towards DNA
* Euchromatin is abundant in Acetylated Lysines

Question 5

Methylation

Answer 5

Methylation of lysines inhibits their acetylation while keeping their (+) charge.
* Heterochromatin is abundant in Methylated Lysines

Question 6

Histone Code:

Answer 6

Specific set of modifications that determines whether a gene is going to be transcribed or not

Question 7

Chromatin Remodeling Complexes (CRC)

Answer 7

Make space inside euchromatin to allow the recruitment of the transcription machinery.

Question 8

Process of Chromatin Remodeling Complexes:

Answer 8

1. Histone modifcation by histone acetyltransferase: LOOSENS attachment of nucleosome to DNA
2. Remodeling proteins bind, disaggregating the nucleosome.
3. Transcription complex can bind to begin transcription.

Question 9

How do activators and inhibitors influence transcription?

Answer 9

They influence transcription from so far away by INDUCING LOOPS that place them in CONTACT to the TRANSCRIPTION MACHINERYassembled at the PROMOTER.

Question 10

Pre-initiation complex of transcription:

Answer 10

General transcription factors + RNA Pol II + Mediator

Question 11

Mediator

Answer 11

Determines whether gene getes transcribed

Question 12

Specific Transcription Factors

Answer 12

Different Activator proteins that bind to an enhancer sequence.

Question 13

Operon

Answer 13

Multiple genes controlled by one promoter

Question 14

4 Types of Promoters:

Answer 14

1. Negative Inducible
2. Negative Repressible
3. Positive Inducible
4. Positive Repressible

Question 15

Negative Inducible Promoter

Answer 15

Substrate makes repressor inactive = transcription ON

Question 16

Negative Repressible Promoter:

Answer 16

Product makes repressor active = Transcription OFF

Question 17

Positive Inducible Promoter:

Answer 17

Substrate makes activator active = Transcription ON

Question 18

Positive Repressible Promoter:

Answer 18

Product makes the activator inactive = Transcription OFF