Translation 2

Front 1

Describe how the start site is indicated on prokaryotic DNA

Back 1

The purine rich Shine-Dalgarno sequence interacts with rRNA, donating the following AUG to be the start site

Front 2

In prokaryotes, what other two sequences can occasionally be the start site other than AUG?

Back 2

GUG or UUG

Front 3

What is an operon?

Back 3

A group of continuous genes that are transcribed into one mRNA molecule

Front 4

What 'p' is a word to describe the mRNA transcribed via an operon?

Back 4

Polycistronic

Front 5

Define polycistronic

Back 5

An individual mRNA that codes for several different proteins

Front 6

How long after transcription does translation begin in prokaryotes?

Back 6

Often, translation can begin before transcription has been completed

Front 7

What is the name of the modified methionine-tRNA complex in prokaryotes?

Back 7

fMet-tRNAf

Front 8

What is the role of the modified methionine?

Back 8

The first amino acid in the sequence - distinguished from the regular methionine amino acids in the protein sequence

Front 9

What is the fate of the modified methionine after translation?

Back 9

Often it is cleaved off

Front 10

Outline the stages in prokaryotic initiation

Back 10

1) Initiation factors (IF) combine with 30s ribosome subunit

2) IF2-GTP delivers fMet-tRNAf and all the components assemble at the start site

3) Meanwhile, 16s rRNA assembles with Shine-Dalgarno sequence

4) tRNA base pairs with AUG codon - IF 1 and 3 disassociate

5) IF2 recruits 50s ribosomal subunit and GTP is hydrolysed

6) IF2-GDP and Pi released

Front 11

What enzyme catalyses the formation of the peptide bond between amino acids and where is it found?

Back 11

Peptidyl transferase - found in the large ribosomal subunit

Front 12

What happens after the transfer of the amino acid to the peptide chain?

Back 12

Large subunit moves forward forming hybrids site with the small subunits. The P in the large subunit now aligns with the small subunit's A site and the E in the large subunit now aligns with the small subunit's P site.

Front 13

What occurs after the large subunit has moved forward?

Back 13

The small subunit moves forward, pulling the mRNA through and forming a new A site

Front 14

What occurs after revelation of the new A site?

Back 14

Uncharged tRNA moves out via the E site. New aminoacyl-tRNA enters the A site.

Front 15

What elongation factor binds the incoming aminoacyl-tRNA?

Back 15

EF-Tu-GTP

Front 16

What effect does the GTP bound state have on codon/anticodon interactions?

Back 16

Base pairing is able to occur, but peptide bond cannot form

Front 17

What happens when the correct aminoacyl-tRNA base pairs at the A site when the GTP bound state is present?

Back 17

Hydrolysis of GTP to GDP, causing a conformational change in Ef-Tu, releasing it from the tRNA and the ribosome

Front 18

Which elongation factor is involved with freeing up the A site of the ribosome?

Back 18

EF-G/GTP

Front 19

Where does EF-G/GTP bind?

Back 19

EF-Tu-GTP binding site on 50s subunit

Front 20

What happens when the GTP of EF-G is hydrolysed?

Back 20

tRNAs and mRNA moves three base distances through the ribosome, freeing up the A site and releasing the uncharged tRNA

Front 21

What occurs at the stop codons?

Back 21

Release factor binds at A site

Front 22

What does peptidyl transferase do in the absence of an amino acid?

Back 22

Catalyses addition of H2O, which hydrolyses the peptide bond between the amino acid in the P site and its tRNA

Front 23

What are release factors structurally similar to?

Back 23

tRNA

Front 24

Name two antibiotics that work by disrupting protein synthesis in prokaryotes

Back 24

Chloramphenicol

Streptomycin