Lesson 4B: Protein Synthesis: Translation

Question 1

Translation

Answer 1

The process of assembling a protein
from the genetic information on an
mRNA molecule

This requires a number of elements
working together:

1. Transfer RNA (tRNA)
2. Ribosomes

Question 2

tRNA

Answer 2

The molecule that carries amino
acids to the ribosomes.

Every tRNA molecule contains an
anti – codon that complements a
codon found on the mRNA strand.

Question 3

Ribosome

Answer 3

A specialized structure that “reads” the
mRNA and co – ordinates the action of the
tRNA and the assembly of proteins

Have 2 subunits:

Small Subunit – reads mRNA

Large Subunit – handles tRNA

The large subunit has 3 binding sites for
tRNA:

A Site (Aminoacyl tRNA Binding
Site)

P Site (Peptidyl tRNA Binding Site)

E Site (Exit Site)

Question 4

Step 1 Initiation

Answer 4

Translation is initiated when an mRNA molecule binds to
an active ribosome.

The ribosome reads the mRNA in the 5’ – 3’ direction.

The ribosome reads the initiator codon (AUG) and the
tRNA that contains the anti – codon base pairs at the A
site bringing the amino acid, methionine.

Question 5

Step 2 Elongation

Answer 5

The tRNA bound to the A – Site of the ribosome slides into the P –Site as the
ribosome moves along the mRNA.

A new tRNA carrying a new amino acid corresponding to the codon exposed in the
A – site binds to the ribosome.

A peptide bond forms between the new amino acid and the amino acid attached to
the tRNA in the P – Site forming a polypeptide chain on the A – site.

The tRNA in the P – Site slides into the E –Site where it is ejected and the process
repeats.

Question 6

Step 3 Termination

Answer 6

Elongation continues until the ribosome reads a “stop” codon on the mRNA
(UAA UAG or UGA)

When a stop codon is encountered a “release” factor binds to the
termination codon and the complete polypeptide chain is released

The chain is then “processed” into a functional protein