Post-transcription and translation

Question 1

What is post-transcriptional gene silencing

Answer 1

Gene silencing small interfering RNA cause mRNA degrade, can’t be translated to protiens

Question 2

What happens if RNA fragments are complementary to mRNA (PTGS antisense mechanism)

Answer 2

Form double stranded RNA - virus RNA often double stranded
Triggers mechanism to destroy it
Triggers small RNA fragment production to be supressed

Question 3

What is a transposon

Answer 3

Small DNA pieces - replicate and move round in genome, insert themselves

Question 4

What has the PTGS mechanism likely evolved from

Answer 4

A way of destroying virus RNA and defending against transposons

Question 5

What are the ways to silence genes

Answer 5

1. sense construct
2. antisense construct
3. RNAi construct

Question 6

What is antisense construct

Answer 6

Take out gene want to silence and turn the sequence around, reinsert - opposite strand is transcribed

Question 7

What is RNA interference construct

Answer 7

Gene coding sequence at start
End is opposite coding sequence (RNA complementary base pair)
If can RNA sequences can bind to form double stranded RNA they get cut out

Question 8

How can DNA packing affect gene not being expressed

Answer 8

Eukaryotes, DNA coiled round protein complexes made of histones, tighter histones are = can turn off sections of chromosomes - DNA cant be read

Question 9

mRNA structure

Answer 9

transcription starts at 5’ end
5’UTR 
start codon
coding region
stop codon
3’UTR
Poly(A) signal
Poly(A) tail

Question 10

What is needed for eukaryotic initiation

Answer 10

Binding initiator tRNA
40S subunit attach to mRNA
Joining of 60S

Question 11

How does translation occur in eukaryote

Answer 11

Scans 5’ UTR, mRNA unwound, more proteins bind
mRNA attaches to complex with poly(A) tail at end
tRNA brings methionine, binds to form large complex

Question 12

What is held in the peptidal tRNA binding site

Answer 12

tRNA that carries amino acid and polypeptide chain

Question 13

What is held in the amino acial tRNA site

Answer 13

tRNA carrying next amino acid to be added

Question 14

How does TRANSLATION termination occur in eukaryotes

Answer 14

Termination codons at end of protein-coding sequence
tRNAs don’t recognise these codons as no (matching) anticodon
Release factors bind to ribosome, release mRNA from ribosome - complex falls apart

Question 15

What must occur before trnaslation

Answer 15

Secondary structure must unwind 5’ UTR region

Question 16

How can the unwinding of the secondary structure be prevented

Answer 16

Inhibiting 5’ cap and 3’ poly(A) tail - inhibition of one promotes the other

Question 17

What can be inferred if initiation does not occur

Answer 17

Don’t need to translate the mRNA at this time - can be degraded

Question 18

Where can mRNA be stored

Answer 18

Vesicles