Translation

Question 1

What are features of the genetic code?

Answer 1

61 of a possible 64 codons specify an amino acid
Most amino acids have more than one codon
Three codons specify to stop (UAA, UAG and UGA)
One codon specifies start (AUG - also specifies methionine)

Question 2

What is tRNA?

Answer 2

Single strand of RNA
70-80 nucleotides in length
At least one tRNA for each amino acid
Each tRNA has a region which can bind an amino acid and region which can interact with mRNA

Question 3

How does tRNA act as the ‘adaptor’?

Answer 3

1. Adaptor between tRNA and RNA is an amino acid binding site - function is to bind amino acids
2. Complementary sequences to mRNA. Anticodon is three nucleotides which binds to and interacts with mRNA
3. tRNA binds to ribosomes. 3D structure - ribosome has pockets which bind tRNA perfectly

Question 4

What are the steps involved in charging a tRNA?

Answer 4

An enzyme recognises both a specific amino acid and the correct tRNA for this amino acid and joins them together
There are 20 different enzymes, one for each amino acid

Question 5

What is Translation?

Answer 5

Translation is the synthesis of proteins by ribosomes using mRNA as a set of instructions. Ribosomes contain both ribosomal RNA (rRNA) and proteins

Question 6

What are ribosomes made up of?

Answer 6

Two subunits, small and large
Large has three binding sites (E, P, A) for tRNA
A: amino acids enter
P: growing chain of amino acids
E: empty tRNA leave

Question 7

What is initiation?
(TRANSLATION)

Answer 7

1. A specific initiation tRNA binds to a small ribosomal subunit
2. The subunit identifies the 5’ G-cap and attaches to mRNA
3. The subunit moves along mRNA (5’—>3’) until it finds AUG
4. Complex stops with initiator tRNA carrying first codon position in P site
5. Large ribosomal subunit attaches

Question 8

What is Elongation?
(TRANSLATION)

Answer 8

1. A charged tRNA with an anticodon complementary to A site codon lands in the A site
2. The ribosome will break bond that binds to amino acid to tRNA and transfer amino acid to the new amino acid forming peptide bond between them, ribosome moves three nucleotides down mRNA
3. In the E site the tRNA detaches from its anticodon and is expelled

Question 9

What is termination?
(TRANSLATION)

Answer 9

1. When the ribosome reaches a stop codon a protein called release factor enters the A site
2. The release factor breaks the bond between P site tRNA using water and the final amino acid. This causes polypeptide chain to detach from tRNA and polypeptide is released
3. The small and large ribosomal sub units dissociate from the mRNA and each other