W10L1 Important feature of translation

Question 1

What should be remembered about post transcriptional and postranlational

Answer 1

-MRNA level doesn’t equal protein level
-There is substantial post-transcriptional and post-translational control of gene expression

Question 2

Why is it important to regulate translation

Answer 2

• Energy: 80% of cellular energy is used in translation, 50% of cell biomass
  -specificity of the process

Question 3

General principles of translation – the ribosome cycle

Answer 3

-1. Initiation
-2. Elongation
-3. Termination

Question 4

Translation in prokaryoter

Answer 4

-Happen in the same time as transcription, creating a unit know as polyribosome

Question 5

mRNAs in prokaryotes

Answer 5

Prokaryotic mRNAs can be arranged in operons
Each ORF (usually) contains a Ribosome Binding Site (Shine dalgarno sequences)

Question 6

Initiation of translation in prokaryotes

Answer 6

-Small subunit associate with translation initiation factor. Recruiting mRNA and the fMet tRNA
-Upsterm 5’ of the mRNA have AGGAG which have complementary to the ribosome sequences
-This place the AUG to the P site of the ribosome with the MET tRNA
-association with the large subunit

Question 7

Way to prevent translation initiation

Answer 7

-An RNA-binding protein in AUG prevents translation initiation
-A secondary structure in the mRNA prevents translation initiation of ORF2.
Translation of ORF1 disrupts the structure permitted translation of ORF2.

Question 8

Comparison of mRNAs in eukaryotes and prokaryotes

Answer 8

-No RBS, mRNA recognised by 5’cap in prokaryote
-mRNAs are (mostly) monocistronic
-Poly-A tai in eukaryotel

Question 9

Features of translation in eukaryotes

Answer 9

Physical separation of transcription and translation
Interaction between poly-A and 5’cap to circularise mRNAs (increase stability)

Question 10

Initiation of translation in eukaryotes

Answer 10

• regconise ion of the 5’ cap by the pre-initiation complex (PIC)
  -scanning for AUG and Kodak sequences (regconise by the tRNA)
• dissociation of eIF subunit
  -association of 60s ribosomal subunit
  -elongation

Question 11

Leaky scan

Answer 11

-It is possible that ribosome pass through a weak AUG, start translation on the second AUG
-The context of the AUG (Kozak sequence) determines efficiency of initiation

Question 12

IRES: cap-independent translation initiation in eukaryotes

Answer 12

-mRNA structure recruits eIFs
-Very rare in eukaroytic mRNAs (~100 in total)
-Viruses use IRES for translation in host cells

Question 13

Codon bias and translation elongation

Answer 13

-There is degeneracy in the genetic code
-however, the codon usage bias and the tRNA pool affect translation elongation even though codon degeneracy exist
-Codon usage can influence rates of translation and protein folding. Region with sub-optimal codon are slower, also help with folding correctly

Question 14

The wobble concept

Answer 14

-Genomes do not contain all 61 tRNA genes (typically ~32)
-the third nucleotide in the anticodon have flexibility in what it can bind
- G can bind with U on top of C
-Idosine, a modified A can pair with CUA
-This allow one tRNA to bind with many codon, coding for the same aa

Question 15

Translation termination

Answer 15

Stop codons are recognized by release factors
in prokaryotes (RF1, RF2)
and eukaryotes (eRF1)
Facilitates peptide hydrolysis and release

Question 16

Nonsense mediated mRNA decay in eukaryotes

Answer 16

• Exon junction complex have mark splice boundaries (upf and ejc)
• premature stop codon due to mutation or alternative splice site ( regulation mechanism)
  -UPF protein interact with EJC leading to deadenylation, decappin and degration

Question 17

Nonstop mediated mRNA decay in eukaryotes

Answer 17

-in no stop, there is no stop codon and even the a tail is translated
-recruitment of RF- like protein which create a poly lys from the poly-A
-mRNA degration and protein degration

Question 18

No-go mediated mRNA decay

Answer 18

-Stalled ribosome also recruit RF like protein
- trigger mRNA degradation

Question 19

Organelle translation

Answer 19

Prokaryote-like gene expression
* Organellar ribosomes (rRNAs)
* Organellar t-RNAs (<32), incomplete even by the wobble rule
* RNA editing occur
* Introns (esp. plants)
* Minimal transcriptional regulation
* RBS/SD-independent translation

Question 20

Superwobble and RNA-editing in chloroplasts and mitochondria, coping with fewer tRNA

Answer 20

-Modified genetic code in mitochondria
-RNA modification of chloroplast anticodon
-Super wobble, U pair with al