FoM:L4 - The genetic code and protein synthesis

Question 1

How does DNA work as the genetic code?

Answer 1

• non overlapping
• degenerate
• triplets
• universal
• stop/start codons

Question 2

What is the open reading frame?

Answer 2

area between initiator and stop codon

Question 3

What is tRNA?

Answer 3

transfer RNA
- formed from longer precursors
- modified bases
- cloverleaf structure
- D, T arms and anticodon loop

Question 4

What is wobble?

Answer 4

• fewer number of tRNAs than number of codons
• 1 tRNA binds to more than 1 codon
• 3rd base in anticodon can base pair unusually

Question 5

What are modified bases?

Answer 5

• in tRNA
• non-standard nucleotides
• covalent modification after transcription

Question 6

How are amino acids activated?

Answer 6

• aminoacyl-tRNA synthetases
• ensures the correct amino acid is coupled to the correct tRNA
• requires ATP, E stored in ester bond between tRNA and aa -> E for peptide bond

Question 7

What are the 3 steps of translation?

Answer 7

1) initiation: formation of initiation complex
2) elongation: addition of further aas
3) termination: recognition of a stop codon

Question 8

What us rRNA?

Answer 8

• overall structure
• ability to position tRNAs on mRNAs
• catalytic activity

Question 9

What 3 sites are in a ribosome?

Answer 9

• aminoacyl tRNA site
• peptidyl tRNA
• exit

Question 10

Outline initiation in translation

Answer 10

• initiation factor binds (met-tRNAmet)
• complex with small subunit binds to mRNA
• proceed until AUG region
• large ribosomal subunit binds with initiator aminoacyl tRNA in P site

Question 11

Outline elongation in translation

Answer 11

• aminoacyl tRNAs picked up by elongation factors with GTP, enter A site
• anticodon is matched against codon (if not its thrown out)
• peptidyl synthetase activity links aa to polypeptide
• empty tRNA in P site, new petidyl-tRNA in A site
• moves forward 1 codon, empty tRNA moves to E, peptidyl-tRNA moves to P (GTP and elongation factor)

Question 12

Outline termination in translation

Answer 12

• stop codon with no corresponding tRNA
• release factor binds to A
• release factor releases polypeptide
• ribosome dissociates