Gene organisation and transcription

Question 1

What are the 3 types of RNA polymerases?

Answer 1

RNA Polymerase I -Transcribes rRNA genes
RNA Polymerase II – Transcribes genes encoding proteins into mRNA
RNA Polymerase III- Transcribes tRNA and 5S RNA genes

Question 2

What is gene transcription?

Answer 2

DNA ——> RNA ——> (Protein)

The initial product of gene expression is always RNA

Question 3

Which strand of DNA is transcribed?

Answer 3

Anti-sense (it is the opposite to the mRNA produced)

Question 4

what is transcription done by?

Answer 4

RNA polymerases

Question 5

Which RNA polymerases which RNA:

• mRNA
• tRNA
• rRNA
• snRNA

Answer 5

mRNA (messenger RNA, involved in Transcription) synthesised by RNA POLYMERASE II
tRNA (transfer RNA, involved in Translation)synthesised by RNA POLYMERASE III
rRNA (ribosomal RNA, involved in ribosome structure)synthesised by RNA POLYMERASE I
snRNA (small nuclear RNA, involved in RNA splicing)synthesised by RNA POLYMERASE II or III

Question 6

What is the gene promoter and its role

Answer 6

TATA sequence + Transcription Factor Binding Site.This is where theinitiation complex assembles
ROLE;
Transcription complex assembles at the gene promoter

Question 7

state the stages at which the transcription factors bind to TATA?

Answer 7

• TF II D
• TF IIA and TF IIB
• RNA polymerase II bind to TF IIB with TF IIF
• TF II E, TF IIH and TF IIJ bind to RNA polymerase II.

Question 8

What is special about TF IID and TF IIH?

Answer 8

TF IID:
- consist of TATA binding protein ( TBP) and TBP accessory factors (TAFs), when TF IID binds to TATA:
/ partially unwinds the DNA and widens minor groove- allowing extensive contact with bases
/ unwinding is asymmetrical with respect to TBP-TATA complex, ensuring transcription is unidirectional

TF IIH:
-promotes further unwinding of the DNA helix to facilitate RNA synthesis by RNA polymerase II.

Question 9

Which transcription factor binds to both RNA polymerase II and TF II D

Answer 9

TF IIB

Question 10

What is the basal transcription complex?

Answer 10

It contains all the TFs and the TATA, without the TFs the basal complex has low level of transcription

Question 11

What do Transcription factors do and give examples?

Answer 11

-facilitate transcription by helping to remodel chromatin. Done by recruiting proteins with enzymatic activity that modify histones.
Hyperacetylation = Gene expression
Hypoacetylation= Gene repression