CMB2001/L07 Post-transcriptional Control I

Question 1

What is the difference in where translation occurs between prokaryotes and eukaryotes?

Answer 1

In eukaryotes, translation occurs outside of the nucleus

Question 2

Give the 4 levels of eukaryotic gene expression regulation.

Answer 2

Transcription control
RNA processing control
Translation control
Protein activity control

Question 3

When are the m7G cap and poly A tail added and what does this mean?

Answer 3

Added post-transcriptionally in eukaryotic mRNAs
Not encoded in the genome

Question 4

What is pre-mRNA?

Answer 4

Unfinished messenger RNA or precursor mRNA

Question 5

How is primary transcript processing coupled to transcription?

Answer 5

Via the RNA pol II CTD which acts as a landing pad

Question 6

Describe the synthesis of the 5’ m7G cap. (2)

Answer 6

GpppN structure - addition of a guanosine triphosphate
Methylation - of guanosine cap which alters chemical behaviour of base and is crucial in function of mRNA

Question 7

Describe the structure of the 5’ m7G cap. (2)

Answer 7

Methylated guanosine at N7 position
Linked to 5’ end via 5’-5’ triphosphate bridge

Question 8

Give 3 functions of the m7G cap.

Answer 8

Protects mRNA from degradation by 5’-3’ nucleases
Facilitates splicing
Facilitates export from nucleus
Critical for translation of most mRNAs
Functions mediated through protein binding

Question 9

What kind of element is the 5’ cap?

Answer 9

Protein-binding

Question 10

How long are introns generally?

Answer 10

80-10,000

Question 11

What is a Duchenne muscular dystrophy?

Answer 11

Muscle wasting disease
Linked to gene dystrophin

Question 12

What 3 conserved sequences are present in introns?

Answer 12

5’ splice site
3’ splice site
Branch site

Question 13

Give the 2 steps of intron splicing.

Answer 13

2 trans-esterification reactions
1) cut at 5’ site & creation of bond between 5’ end of intron and branch site
2) cut at 3’ splice site to release intron lariat & ligation of two exons

Question 14

What is the spliceosome?

Answer 14

Enzymatic complex that catalyses the removal of introns

Question 14

What kind of proteins are within the spliceosome? (3)

Answer 14

RNA-binding proteins
ATPases
GTPases
Several snRNPS (U1-2, U4-6)

Question 15

What is splicing catalysed by?

Answer 15

snRNAs

Question 16

What do snRNPs bind to?

Answer 16

Base-pair with conserved sequences in intron
(U1 with 5’ splice site, U2 with branch point)

Question 17

What do snRNAs code for?

Answer 17

Nothing - non-coding

Question 18

Where are snRNPs found?

Answer 18

In the nucleus

Question 19

What are anti-Sm antibodies and which disease is associated with them?

Answer 19

Reactant against Sm proteins
Systemic lupus erythematosus (SLE)

Question 20

What are SM proteins?

Answer 20

Essential components of snRNPs which aid in assembly and stability

Question 21

How are transcription and splicing functionally coupled?

Answer 21

Such that they influence one another

Question 22

Why is the number of proteins more than the number of genes in the genome?

Answer 22

Alternative splicing allows many proteins to be made from the same genes

Question 23

Give 3 types of alternative splicing.

Answer 23

Exon skipping
Intron retention
Mutually exclusive exons
Alternative 5’ splice site
Alternative 3’ splice site

Question 24

Where do activators bind?

Answer 24

Intronic (ISE) and exonic splicing enhancers (ESE)

Question 25

Where do repressors bind?

Answer 25

Intronic (ISS) and exonic splicing silencers (ESS)

Question 26

How can mutants cause defects in splicing?

Answer 26

Loss of protein function Only one protein isoform

Question 27

What is the effect of spinal muscular atrophy on infants?

Answer 27

Most common genetic cause of infant mortality

Question 28

What are the effects of retinitis pigmentosa?

Answer 28

Reduced visual capabilities and blindness