PL5 : Translation 2 (elongation and termination)

What are ribosomes responsible of?

All protein synthesis.

Which is the most abundant RNA-protein complex in the cell?

The ribosomes

At what rate does elongation proceed?

3 -5 amino acids/second

What is peptidyltransferase activity?

Creation of peptide bonds in growing polypeptide chain without protein.→ enzymatic activity in RNA molecule called ribozyme

Which structure is responsible of peptide transferase activity?

In bacteria : 23s rRNA; in eukaryotes : 28s rRNA

Explain translation elongation in y steps:

Again flame:

Explain translation termination

When stop codon at A site : eRF1 (termination release factor) associated with GTP-bound eRF3 bind to A site → cause GTP hydrolysis
Result : cleavage of polypeptide chain on P site tRNA

Disassociation of large and small ribosomal subunit so that ready to be used again.

Put these 3 events in order : peptide cleavage, release of tRNA at E site and release of polypeptide chain

1- peptide cleavage 2- release of the 2 other things

What favors the reinitiation of translation? How?

Interaction of the s' and 3' ends of the mRNA

They create a loop
mRNA stabilization = efficient transcription

What does ribosome profiling enable?

- Detailed measurement of translation
- instantaneous measurement while others measure are steady state.

What does ribosome profiling do?

It quantifies the levels of new protein synthesis and gives information on where the ribosomes are ( helped to discover new translation products)

How is ribosome profiling done?

1 - Isolation of mRNA ASSOCIATED with ribosomes
2 - cleaved with nuclease : not affected if associated with ribosomes = ribosome footprints
3 - Sequencing and mapping of ribosome footprints which should indicate reading frames ; the more they are present the more they should be actively translated

If gene A is sequenced 10x more than gene B, does it mean that gene A is translated 10x more efficiently than gene B?

NOOOOOOOOOO!

How can we correcly interpret result from ribosome profiling?

We need to compare the ratio of ribosome-bound mRNA to the ratio of total mRNA.

If they are the same, both genes are as efficiently translated.
If they are different, the one that has a bigger ribosome-bound ratio is translated more efficiently