L8 - RNA Transcription

Question 1

What is transcription?

Answer 1

The process of RNA synthesis from a DNA template

Question 2

mRNA

Answer 2

Messenger RNA
Codes for proteins
3-5% of total RNA

Question 3

tRNA

Answer 3

Transfer RNA
Participates in translation carrying amino acids
Each has a specific anticodon loop

Question 4

rRNA

Answer 4

Ribosomal RNA
Major constituent of ribosomes
4 main types

Question 5

Primary structure of RNA

Answer 5

Ribose instead of deoxyribose
Uracil instead of thymine
Synthesised as a single strand
Very unstable

Question 6

Secondary structure of RNA

Answer 6

A binds to U
G binds to C
Can also have non Watson Crick airing
- G binds to U
Give rise to stem loop secondary structures that can base pair on themselves through H bonds

Question 7

Tertiary structure of RNA

Answer 7

Folding of a molecule in 3D

Question 8

RNA polymerase I

Answer 8

Ribosomal RNA

Question 9

RNA polymerase II

Answer 9

Protein encoding genes

Question 10

RNA polymerase III

Answer 10

tRNA, snRNA, 5s rRNA

Question 11

Differences between RNA and DNA transcription

Answer 11

Multiple RNA polymerases bind on the same gene
No primer needed
Only one strand of DNA is used as the template
Transcript does not remain bound to the template
Higher error rate

Question 12

What direction does RNA transcription occur?

Answer 12

5’ to 3’ direction
RNA polymerase moving from left to right - RNA made using bottom strand as template
RNA polymerase moving from right to left - RNA made using top strand as template
Template strands described as antisense

Question 13

Transcription creates supercoiling

Answer 13

DNA with fixed end

- Unwind 10 DNA base pairs - DNA helix forms one supercoil

Question 14

What do topoisomerases do?

Answer 14

Release supercoils to allow progression

Question 15

Where does transcription start?

Answer 15

Promoter
Sequences in the DNA tell RNA polymerase where to start 
- INR
- BRE
- TATA 
- DPE

Question 16

Many proteins in the polymerase complex bind directly to DNA including

Answer 16

TATA binding protein binds to TATA box found upstream

Question 17

Protein complex is required for transcription to start

Answer 17

General and specific transcription factors

Question 18

RNA processing techniques

Answer 18

Splicing of introns
Capping of 5’ end
Polyadenylation of 3’ end

Question 19

Splicing of introns

Answer 19

Eliminates non-coding intron regions to generate mature mRNA for protein synthesis
Specific to eukaryote mRNA
Some mRNA can be spliced multiple ways - alternative splicing

Question 20

Capping of 5’ end

Answer 20

Necessary for

• Stability
• Binding of mRNA to ribosomes
• Initiation of translation

Question 21

Polyadenylation of 3’ end

Answer 21

Part of termination process
Addition of PolyA tail
Determine mRNA stability
Helps mRNA nuclear export and translation
Cleavage is 1-30 nucleotides downstream of PolyA signal

Question 22

Splicing mechanism

Answer 22

1. OH of branch site A attacks bond on donor site G
2. Cleavage at donor site leads to formation of a lariat ]
3. 3’ OH donor site G attacks bond on acceptor site G
4. Lariat is freed then degraded

Question 23

What is mRNA splicing performed by?

Answer 23

Splicesome - nuclear complex made of 150 proteins + 5RNAs

Question 24

Functions of the splicesome

Answer 24

Recognise 5’ donor and branch sites
Bring sites together
Catalyse RNA cleavage

Question 25

Synthesis of 5’ cap mechanism

Answer 25

1. Cap added early on when mRNA is 20-40 nucleotides long
2. Unusual 5’ to 5’ linkage of guanosine
3. Methylation of guanine

Question 26

Recognition of PolyA signal

Answer 26

PolyA signal - AAUAAA

CPSF and CstF recognise the signal and bind to it

Question 27

What is CPSF?

Answer 27

Cleavage and polyadenylation specific factor

Question 28

What is CstF?

Answer 28

Cleavage stimulating factor
Helps in recruiting PolyA polymerase which adds on up to 200 As
PolyA binding proteins bind to the As

Question 29

What is CTD?

Answer 29

Pol II C-terminal domain

Binds to proteins waiting for the PolyA signal to keep them there