Translation - tRNAs and the Ribosome

Question 1

How are codons ‘read’?

Answer 1

Adaptor molecules are used - a special class of RNA - tRNA
- Each carries an amino acid
- Recognises at least one codon for a single amino acid

Question 2

tRNA molecules’ defined structure

Answer 2

• Internal base pairing in a ‘clover leaf’
• Has modified bases
• 4 loops: anticodon, DHU, T-psi-C, variable
• Amino acid is attached at 3’ end
• Anticodon is complementary to the codon on the mRNA

Question 3

Clover leaf structure folds to L shape

Answer 3

• 2 helical regions + a bend
• 2 constant loops (DHU, T-psi-C) form the ‘elbow’/bend
• Anticodon loop on one end of ‘L’ and amino acid on attached to other

Question 4

‘Charging’ the tRNA

Answer 4

2 Step reaction
- AMP attached to carboxyl group of amino acid
- AA then transferred from AMP molecule to the tRNA

-AMP and PPi are released
- Reaction is driven by breakdown of PPi to 2Pi

Question 5

Enzyme involved with charging tRNA

Answer 5

• Aminoacyl-tRNA synthetase attaches each amino acid to its corresponding tRNA molecule to ‘charge’ it

Question 6

Ribosomes

Answer 6

• Where translation occurs, containing a large + small subunit
• Prokaryotic contain over 50 proteins + 3 ribosomal RNAs (rRNA)
• Eukaryotic ribosomes contains over 80 proteins + 4 rRNAs