Biochem 1 - genetics and epigenetics

Question 1

What are the 5 main levels of gene expression?

Answer 1

1. genome
2. transcription
3. RNA processing and nuclear export
4. translation
5. posttranslation

Question 2

How many base pairs does a chromosome contain?

Answer 2

48 - 240 million base pairs

Question 3

What are epigenetic mechanisms?

Answer 3

modifications of DNA that switch specific gene expression on/off

Question 4

What does methylation of DNA affect?

Answer 4

gene expression
- methylation is generally associated with regions of DNA that are less actively transcribing RNA, usually shuts of expression

Question 5

What are promoters?

Answer 5

promoters are DNA sequences upstream (in front) of the coding sequence

they ‘tell’ RNA Polymerase where to start transcription and which DNA strand to transcribe

Question 6

What do promoters bind?

Answer 6

promoters bind proteins called transcription factors (TF)

Question 7

What are transcription factors (TF)?

Answer 7

proteins that specifically recognise the DNA sequence

some transcription factors stimulate expression, some suppress, some are ubiquitous

Question 8

What are the 2 functional domains of Transcription Factors?

Answer 8

1. DNA-Binding domain
2. Transcriptional activation domain

Question 9

What does the DNA-binding domain do/contain?

Answer 9

interact with DNA via the major or minor groove
- helix-turn-helix motif (due to protein shape)
- leucine zipper motif
- zinc finger motif

Question 10

What does the Transcriptional activation domain do?

Answer 10

• stimulate the formation of an active transcription complex
• may interact with the RNA Polymerase complex
• indirect effetcs from interaction with coactivators and corepressors
• may remodel the chromatin

Question 11

Why might transcriptions factors need to be able to remodel the chromatin?

Answer 11

Part of the control of gene expression depends on the availability of a gene to be transcribed, so this may require the DNA unwinding from the histones and becoming physically available for transcription to take place.

Some transcription factors can cause this unwinding to happen.

Question 12

What are enhancers?

Answer 12

• DNA sequences which can up-regulate transcription
• enhance formation of initiation complex

Question 13

What are silencers?

Answer 13

DNA sequences which can down-regulate transcription