Energetics of Translation (Protein synthesis)

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Energetics of Translation

A. High energy bonds for synthesis of polypeptide chain of (N) amino acid residues N ATP to charge tRNA

1 GTP for initiation
N-1 GTP for binding of aa-tRNA to A-site N-1 GTP for translocation step
1 GTP for termination
Sum: 3N
300 aa protein requires 900 high energy bonds; Each bond is 7.5 kcal/mol 900 bonds × 7.5 kcal/bond = 6,750 kcal/mol polypeptide 22.5 kcal/bond
Free energy of peptide bond hydrolysis is –0.5 kcal/mol At 10% energy conversion, –5 kcal would be sufficient to form a peptide bond.

B. High price paid for synthesizing a defined sequence.

1. Random polymerization is cheaper
2. Only one high energy bond is involved in peptide bond formation
3. Cells need to proofread to insure defined sequence.

4. The ultimate step in gene expression must be correct.



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