Protein synthesis

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Protein Synthesis
R. C. Gupta M.D. (Biochemistry) Jaip
ur (Rajasthan), India
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An overview of protein synthesis

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Amino acids are present in cytosol
They bind to specific tRNA molecules
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This is known as charging of tRNAs
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Gene expression
Gene expression means using the information
present in the gene to synthesize a protein
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A gene is expressed when the protein encoded by
it is required
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Transcription of gene
For expression of a gene, the coded infor-
mation present in it has to be transcribed
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Charging of tRNAs
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Wobble
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Translation
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Initiation
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Dissociation of ribosomal subunits
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Formation of 43S pre-initiation complex
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Formation of 48S initiation complex
eIF-4F binds to the 5 cap of mRNA
eIF-4A and eIF-4B bind to mRNA in the presence of
ATP
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IF-4A hydrolyses ATP into ADP and Pi

Using this energy, eIF-4B uncoils the
mRNA near its 5-end
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Formation of 80S initiation complex
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Elongation
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• This activity is present in the 28S rRNA which
  is a ribozyme

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Termination
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Polysome
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Post-translational modifications
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Cleavage
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Hydroxylation
Some amino acid residues, e.g. proline and
lysine, may be hydroxylated after translation
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Carboxylation
Glutamate residues of pre-prothrombin are
carboxylated after translation
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This converts pre-prothrombin into prothrombin
Glutamate residues of several other proteins are
also carboxylated
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Phosphorylation
Serine, threonine and tyrosine residues of some
proteins can be phosphorylated
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Phosphorylation is a method used for regulating
the activity of some enzymes
Phosphorylation of tyrosine residues is important
in intracellular signaling
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Glycosylation
Carbohydrate prosthetic groups are added to many
proteins
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Examples are mucin, immunoglobulins, hCG etc
These can form O-linked, N-linked and
GPI-linked glycoproteins
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The linkage between carbohydrate portion and
protein occurs through
Hydroxyl group of serine in
O-linked glycoproteins
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Amide group of asparagine in N-linked
glycoproteins
Phosphatidyl inositol in GPI-linked glycoproteins
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Addition of other prosthetic groups
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Prokaryotic translation
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Primary transcript
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Number of cistrons
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Number of initiation sites
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Shine-Dalgarno sequence
5------AGGAGGU?NNNNN?AUG---
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Initiation factors
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Elongation factors
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Releasing factors
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Protein folding
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Some protein factors
Some enzymes
Chaperone proteins
Chaperonins
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Enzymes involved in protein folding
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Protein targeting
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The signal that directs the protein to its
destination is inbuilt in the protein molecule
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Signal hypothesis
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Streptomycin
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Tetracyclines
Tetracyclines bind to 50S ribosomal subunit of
prokaryotes They prevent binding of amino acyl
tRNA to the A site
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Chloramphenicol
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Erythromycin
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Thank you