The Genetic Code - Lecture 15

Question 1

What is a codon?

Answer 1

A 3 nucleotide or triplet code used to specify amino acids

Question 2

What was the Nirenebrg-Matthaei experiment?

Answer 2

○ Used RNA that only contained U (Poly U) and 20 amino acids and one of them was radiolabelled
○ Added that to bacterial extract competent for translation
○ Isolate polypeptides and measured how much radioactivity was in the protein
○ Only labelled Phe gave a labelled polypeptide
○ Did this with different templates

Question 3

What is an open-reading frame?

Answer 3

Runs from a specific start codon to a specific stop codon

Question 4

What is the function of tRNA?

Answer 4

○ To link a specific amino acid and to recognise a codon in mRNA
○Ensures amino acid-codon match

Question 5

How does the structure of tRNA aid its function?

Answer 5

○ Has an acceptor arm where the amino acid joins to
○ Modified nucleotides especially in anticodon loop

Question 6

What is aminoacyl-tRNA synthetases?

Answer 6

○ Each tRNA is recognised by only one of 20 aminoacyl-tRNA synthetases
○ Each synthetase is specific for amino acid and tRNA
○ >1 tRNA for some amino acids so some tRNAs recognise more than one codon

Question 7

What is wobble?

Answer 7

Allows unconventional base pairing between third base in codon and first base in anticodon

Question 8

What does wobble allow?

Answer 8

○ Most variation at the third position
○ Purine -> any pyrimidine (vice versa)
○ Inosine (modified G) -> A, C, U