By:MARYAM SHAKEEL

TRANSLATION IN PROKARYOTES

INITIATION ELONGATION TERMINTION

TRANSLATION:The process in which the messenger RNA (mRNA) generated by transcription is interpreted by the ribosome to generate a particular amino acid succession, or polypeptide that will fold into an active protein.STAGES

:

Bringing the Small Ribosomal Subunit to the Initiation Codon

Binding of small ribosomal subunit to the initiation codon at m-RNA.

How small subunit of ribosomes select initiation codon

Initiation factors IF1,IF2,IF3

INITIATION

Shine-Dalgarno Sequence

Bringing the first aa-tRNA into the ribosome

AUG is an initiation and only one codon for METHIONINE.

t-RNA enter at P site and bind to both AUG & IF2

Assemble complete Initiation complex

Larger subunit join complex GTP hydrolyse IF2-GDP release

It is always first amino acid in polypeptide

chain

Aminoacyl-t RNA Selection

Entry of second aminoacyl-tRNA in A site

EF-Tu is require to deliver aminoacyl-tRNA to A site

Complex of aminoacyl-tRNA Tu-GTP enter

GTP is hydrolyse and Tu-GTP release

ELONGATION

Must join EF-Tu bound to GTP

Series of steps is repeated over and over as amino acids are polymerised in growing polypeptide chain

Peptide Bond Formation Two amino acid, attached with separate

tRNA are juxtaposed in such position that the can react

Amine nitrogen of the aa-tRNA in A site carries out a nucleophilic attack on carbonyl carbon of amino acid bound to tRNA of P site

As a result tRNA at A site Dipeptide tRNA in P site deacylated Pepti

de bond formed

Peptidyl

transferas

e

Formed

spontaneouslyA component of large

ribosomal subunit known as ribozyme.

TRANSLOCATION It is actually

characterized by a ratchet-like motion of ribosomes

Dipeptidyl-tRNA shift from A site P site

GTP hydrolyse and EF-G-GDP leaves

Ribosomes moves three nucleotide along mRNA in 5’-3’ direction

Releasing the Deacylated tRNA

Deacylated tRNA leaves ribosome

Empty E site

STOP CODON

Class 1 RFs RF1, RF2 Class 2 RFs GTP binding protein

TERMINATION

Release Factor

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