Question

Calculate the energy required, in ATP equivalents, to synthesize a 100-residue protein from free amino acids in E. coli (assume that the N-terminal Met remains attached to the polypeptide and that no ribosomal proofreading occurs).

Short answer

In E. coli, synthesizing a protein with 100 residues from free amino acids takes about 400 ATP equivalents.

Step-by-step solution

Adenosine triphosphate (ATP)

The main molecule for storing and transferring energy in cells is adenosine 5'-triphosphate (ATP). It is frequently referred to as the cell's energy currency. In particular, it is a coenzyme that transfers energy to cells by releasing phosphate groups when interacting with enzymes like ATP triphosphatase.

ATP equivalent required to synthesize 100-residue protein

During translation, amino acids are attached to tRNA, and this process is referred to as aminoacylation.Aminoacylation involves the hydrolysis of ATP.

• As pyrophosphate is cleaved from ATP during aminoacylation, 200 ATP equivalents are needed to aminoacylate 100 tRNAs.
• 1 GTP is needed for initiation of translation which is equivalent to 1ATP.
• For the action of EF-Tu, 99 cycles of elongation require 99 GTP (equivalent to 99 ATP equivalents).
• For EF-G action, 99 cycles of ribosomal translocation require 99 GTP (equivalent to 99 ATP equivalents).
• Finally, 1 GTP (equivalent to 1 ATP equivalent) is needed for translation termination.

Hence, 200 + 1 + 99 + 99 + 1 = 400 ATP equivalents are required for the 100 amino acid residue protein.