Protein Biosynthesis

By

Amr S. Moustafa, M.D.; Ph.D.

Components of Translation

Amino acidsThe tRNAAminoacyl-tRNA synthetasesThe mRNACompetent ribosomesProtein factorsATP and GTP

Aminoacyl-tRNA

Synthetases

Activated amino acid

Charged tRNA

Wobble Hypothe

sis

Competent Ribosomes

Protein Biosynthesis

Translation:Genetic code on mRNA to amino acids on proteins

Polycistronic Vs Monocistronic

Steps:InitiationElongationTermination

Posttranslational modifications

Protein Biosynthesis: Initiation

Complementarity: 5’-end mRNA and 3’-end 16S rRNA

Shine-Dalgarno sequence

Protein Biosynthesis: Initiation-2

Initiation complexAssembly of components of translation:

The mRNA2 Ribosomal subunitsAminoacyl-tRNAGTPInitiation factors (IF or eIF)

Protein Biosynthesis: Initiation-3

Initiation codonAUG for metthionine

Initiator tRNA: IF-2 and P-site

N-Formylated methionine:

Transformylase

N10-formyl tetrahydrofolate

After binding to tRNA

Removal of N-formyl methionine

Protein Biosynthe

sis: Initiation-

4fMet-tRNA

Protein Biosynthesis: Elongation

Addition of amino acids to the carboxyl end

Elongation factors: EF-Tu, EF-Ts (eEF)

Peptidyltransferase: 23S rRNA (ribozyme) and GTP

Translocation: Ribosome moves in 5’-3’ on mRNAEF-G and GTPMovement of uncharged tRNA to E-siteMovement of peptidyl-tRNA to P-site

Protein Biosynthesis: Termination

Termination codons at the A-site

RF-1: UAA and UAGRF-2: UAA and UGARF-3: Binds GTP

Termination:Release of newly synthesized polypeptideDissociation of ribosome from mRNARecycling: Ribosomal subunits

mRNA and tRNAprotein factors

eRF: Single release factorBinds GTP

Peptide bond formation

Polyribosome: Several ribosomes and one mRNA