Translation - DNA to RNA to protein

Question 1

Initiation of translation in prokaryotic - Shine-Dalgarno / Ribosome Binding Site

Answer 1

• A sequence upstream from the mRNA’s start codon that tells the ribosome where to start translating
• Binds the 16S rRNA

Question 2

Components required for prokaryotic translation

Answer 2

• Ribosomes
• mRNA
• fMet-tRNA(fmet)
• initiation factors (IFs)

Question 3

What is needed for the assembly of the translation apparatus?

Answer 3

One molecule of GTP

Question 4

How translation is intiated in prokaryotes

Answer 4

• Initiating tRNA (fMet-tRNA(fMet)), small ribosomal subunit + mRNA form a complex
• This is followed by binding of large ribosomal subunit
• Then ready for elongation phase

Question 5

Initiation of translation in eukaryotic - eIF

Answer 5

• ‘Eukaryotic Initiation Factors’ help the ribosome bind to the 5’-Cap and find the first AUG codon (start)
• Don’t contain a Shine-Dalgarno sequence or equivalent

Question 6

How translation is initiated in eukaryotes

Answer 6

• Initiating tRNA (Met-tRNA(Met), small ribosomal subunit and the mRNA form a complex
• Then large ribosomal subunit binds
• Ready for elongation phase

Question 7

Components required for eukaryotes

Answer 7

• Ribosome
  -mRNA
• Initiation Factors (eIFs)

Question 8

What is needed for the assembly of translation apparatus in eukaryotes?

Answer 8

1 ATP + 1 GTP

Question 9

The P (peptidyl) Site - Step 1

Answer 9

• At beginning of each cycle, the growing peptide chain is attached to the tRNA

Question 10

The A (aminoacyl) Site - Step 2

Answer 10

• Incoming aminoacyl-tRNA is delivered by an elongation factor (EF-Tu/eEF1alpha) to here - GTP needed
• A decoding centre in A make sure the right aa-tRNA is delivered

Question 11

How the peptide bond is formed - Step 3

Answer 11

• Growing chain is transferred from t-RNA in P site
• To the amino group of the AA is carried by the tRNA in the A site
• Peptide bond is formed
• The peptidyl transfer reaction is catalysed by peptidyltransferase activity of ribosome

Question 12

Ribosome moves along the mRNA - Step 4

Answer 12

• This translocation step requires an elongation factor (EG-G/eEF2) and GTP
• tRNA carrying the growing peptide –> P site
• Uncharged tRNA –> Exit site (E)
• A site is now occupied by next codon on mRNA

Question 13

Where the uncharged tRNA goes + how the cycle continues - Step 5

Answer 13

• Leaves the ribosome and the next aminoacyl-tRNA is delivered to the A site by EF-Tu

Question 14

Termination of translation

Answer 14

• When the stop codon occupies the A site, no aminoacyl-tRNA can bind to A site
• Release factors bind to A site to release new protein from ribosome
• Factors (RRF, EF-G, IF3) lead to release of uncharged tRNAs & large + small ribosomal subunits dissociate