Translation

Question 1

Eukaryotic ribosomes are a complex of

Answer 1

rRNA and 82 ribonucleoproteins

40S + 60S assemble into the 80S ribosome for translation

Question 2

Steps of translation (3)

Answer 2

• initation
• elongation
• termination

Question 3

Translation begins with the codon

Answer 3

AUG

Which codes for methionine carried by a special tRNA called an initiator tRNA

Question 4

The initiator tRNA carries

Answer 4

Methionine and binds to the P site of the small subunit before the ribosome is fully assembled

Question 5

Eukaryotic initiation factors (eIFs) functions (2)

Answer 5

• help load the initiator tRNA into the small subunit of the ribosome
• help bind the 5’ end of mRNA into the ribosome

Question 6

eIF4E binds

Answer 6

to the 5’ GTP cap

Question 7

EPA are the

Answer 7

tRNA binding sites in the ribosome

Question 8

Translation terminates with the codon

Answer 8

UAA/UAG/UGA

release factors bind to the A site containing the stop codon forcing peptidyl transferase to hydrolyse water instead of an a.a.

Question 9

Post translational modifications (6)

Answer 9

• phosphorylation (via kinases: cell cycle and signal transduction)
• methylation (via methyl transferases: inc+ hydrophibicity and epigenetics)
• glycosylation (affect protein folding and conformation)
• proteolysis (activating proteins)
• n-acetylation (transfer acetyl group to N terminus to replace Met, gene expression regulation)
• lipidation (inc+ hydrophibicity, destined for membranes)

Question 10

mRNA turnover is the

Answer 10

rate at which mRNA is degraded

mRNA is degraded by nucleases, the exosome and decapping proteins

Question 11

Steps of mRNA degradation (2)

Answer 11

• RNA deadenylase + exonucleases degrade the poly A tail

- Decapping proteins + Xrn1p remove the 5’ GTP cap

Question 12

mRNA degradation is determined by

Answer 12

RBPs
RNA binding proteins

bind specific sequences within mRNA that regulate stability

Question 13

What binds to RBPs to increase degradation

Answer 13

AREs

AU rich elements

Question 14

What binds to RBPs to decrease degradation

Answer 14

CREs

stabilise mRNA

Question 15

Nonsense mediated decay is

Answer 15

an mRNA surveillance system that selectively degrades transcripts containing PTCs

PTC= premature termination codon

Question 16

PTCs can form via (3)

Answer 16

• point mutations
• frame shifts
• splicing errors

Question 17

PTCs are recognised during

Answer 17

translation

exon exon junction complexes are protein complexes that have been formed through splicing
these are removed after translation
if any remain, NMD is activated

Question 18

Exon exon junctions are

Answer 18

proteins that form a complex marking the site of a successful splicing event

if any remain on the mRNA after translation, NMD is activated

Question 19

miRNAs

Answer 19

micro RNAs

small non-coding RNA molecules (about 22 nucleotides)

function in RNA silencing and post-transcriptional regulation of gene expression via base-pairing with complementary sequences within mRNA molecules

Question 20

lncRNAs

Answer 20

long non coding RNAs

also regulate mRNA stability

Question 21

Genes can be regulated by (6)

Answer 21

• changes in chromatin
• transcriptional changes
• changes in mRNA processing
• altered translation
• altered mRNA turnover
• ncRNAs