Lecture 25

Question 1

Most abundant RNA-protein complex

Answer 1

Ribosome

Question 2

Final Initiation complex

Answer 2

80S

Question 3

EF1a

Answer 3

in a complex with GTP and the tRNA and is place on the A site of the ribosome. The EF1a is released and hydrolysis of the GTP to GDP causes a conformational change in the ribosome thus bringing tRNA 2 close to 1.

Question 4

First peptide bond formation

Answer 4

The 2 amino acids alpha amino group reacts with activated methionine on initiator tRNA thus release tRNA from the P site. (peptidyl tranferase)

Question 5

Hydrolysis of GTP in EF2

Answer 5

this promotes the translocation of the tRNA molecules from the P and A site to the E and P site

Question 6

Second elongation cycle

Answer 6

The E site tRNA is kicked out following the conformational change of the ribosome (hydrolysis of GTP) and same cycle repeats

Question 7

Translation Termination

Answer 7

When reached a stop, eRF1 recognizes sequence (mimics aminoacyl-tRNas
GTP-bound eRF3 associated to eRF1 bound to A site undergoes GTP hydrolysis thus cleaving the last amino acid in P site

Question 8

Peptide cleavage

Answer 8

Done by the hydrolysis of eRF3 associated with eRF1 and and then the E site tRNA is released then the complex dissacociates

Question 9

5’ and 3’ interactions

Answer 9

PolyA tail factors interact with the 5’ end and the loops favour reinitiating

Question 10

Ribosomal Profiling

Answer 10

Quantifies levels of new protein synthesis and provides info of ribosome positions
Enables instantaneous results

Question 11

Ribosomal Profiling Method

Answer 11

the protected mRNA sequences by rRNA is sequenced and used to map the genome and the more it is found the more actively it is transcribed

Question 12

Interpretation of Ribosomal Profiling:

You recover sequences from gene A ten times more frequently than you recover sequences from gene B

Answer 12

ten times more mRNA for gene A than B but there translational activities are not changed

Question 13

How to analyze translational activities of RIbosomes

Answer 13

Ribosome Profiling and regular sequencing and then normalization

Question 14

From the ribosome profiling reads, the ratio for gene A: gene B is 10:1, and from the total mRNA reads, the ratio for gene A: gene B is 1:1

Answer 14

Gene A mRNA is translated 10 times more efficiently than gene B mRNA.

Question 15

From the ribosome profiling reads, the ratio for gene A: gene B is 10:1, and from the total mRNA reads, the ratio for gene A: gene B is 10:1

Answer 15

Translational efficiency is equal for genes A and B. There is more mRNA for gene A than for gene B, which could result from higher transcription, higher RNA stability, or both.