Translation

tRNA

• The process of assembling a protein from

the genetic information on an mRNA

molecule

“cooking from a recipe”

“building from instructions”

• Transfer RNA

• “t” shaped molecule that links each codon

on the mRNA molecule to its specific amino

acid

Amino Acid

Attachment

Site

Anti – Codon

Arm

Anti – Codon:

3 base pair sequence that is

complimentary to a specific

codon on an mRNA

Amino – Acyl Arm

Ribosomes • A specialized structure that “reads” the

mRNA and co – ordinates the action of the

tRNA and the assembly of proteins

Have 2 subunits:

1. Small Subunit – reads mRNA

2. 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)

The Process

The Process:

Step #1

Initiation

• mRNA binds to an active Ribosome

• Binds in a way that 2 neighbouring codons

are exposed

• Ribosome reads the mRNA in the 5’ to 3’

direction

• Ribosome reads the initiator codon (AUG)

and the initiator tRNA carrying the amino

acid methionine binds to the A – Site of

the Ribosome

Step #2:

Elongation

• 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 larger

polypeptide chain

• The tRNA in the P – Site slides into the

E –Site where it is ejected and the process

repeats.

Step #3:

Termination

• Elongation continues until the ribosome

reads a “stop” codon on the mRNA

• 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