Trans-translation and ribosomal peptidyl transferase Flashcards Preview

BS2091 Biochemistry I: from genes to proteins > Trans-translation and ribosomal peptidyl transferase > Flashcards

Flashcards in Trans-translation and ribosomal peptidyl transferase Deck (23):
1

Bacteria face a major problem during trans-translation when ribosomes..

Become stranded on non-stop mRNA

2

What is non-stop mRNA?

Broken mRNA lacking a stop codon

3

Can you get multiple ribosomes trapped on non-stop mRNAs?

Yes, in polyribosomes

4

What is tmRNA used for?

To release incomplete polypeptides (with C-terminal tags) from ribosomes on non-stop mRNA

5

What does tmRNA resemble?

tRNA lacking an anticodon stem-loop but with an 'extra' mRNA-like region (MLR) containing an open reading frame that can be translated

6

What is the ORF in the tmRNA used for?

To put a C-terminal tag on truncated peptide during release from non-stop mRNA

7

What gene encodes the 363 nucleotide E. coli tmRNA?

ssrA gene

8

What tmRNA tag is the target for proteases such as ClpXP?

ANDENYALAA

9

What does tmRNA (ssrA RNA) work together with?

SmpB protein
Forms quaternary complex with EF-Tu + GTP and binds into ribosomal A site

10

Outline the steps that follow when tmRNA-SmpB binds in A site?

- Peptide bond formation
- Translocation brings tmRNA ORF into A site
- ORF of tmRNA is now being translated; aatRNA binds into A site
- Translation of tmRNA ORF generates C-terminal tag on truncated protein; peptide bond formation

11

How many amino acids does the tmRNA ORF encode?

10 amino acid sequence

12

Are ribosomes recycled?

Yes

13

Is the alanine in the tag coded for?

No, it's inserted into empty decoding site

14

What terminates the synthesis of the tag?

UAA stop codon

15

What does PTC stand for?

(Ribosomal) peptidyl transferase centre

16

What are the CCA-3' ends of tRNAs in the PTC positioned for?

Peptide bond formation by specific H-bonding to P-loop and A-loops of 23S rRNA

17

What does puromycin resemble?

The 3' end of aa-tRNA

18

What is puromycin?

An acceptor substrate for peptidyl transferase

19

What happens when the nascent peptide is joined to puromycin?

The peptidyl-puromycin falls off ribosome

20

Is the PTC on the larger or smaller ribosomal unit?

The larger one

21

What do the donor substrates in the P site need?

2'-OH

22

What is the 2'-OH of the P site involved in?

Proton shuttle

23

What are the 3'-CCA ends of tRNAs held in position at the PTC by?

The P-loop and A-loop of 23S rRNA