I

|gtp|gtp| gtp |gtp|gtp|gtp|gtp aaï—aa5—aa3 — aa9— aa2—aa13—aa20

Figure 3-11

Chemical events in the formation of a protein molecule.

process in which ATP combines with the amino acid to form an adenosine monophosphate complex with the amino acid, giving up two high-energy phosphate bonds in the process. (2) The activated amino acid, having an excess of energy, then combines with its specific transfer RNA to form an amino acid-tRNA complex and, at the same time, releases the adenosine monophosphate. (3) The transfer RNA carrying the amino acid complex then comes in contact with the messenger RNA molecule in the ribosome, where the anticodon of the transfer RNA attaches temporarily to its specific codon of the messenger RNA, thus lining up the amino acid in appropriate sequence to form a protein molecule. Then, under the influence of the enzyme peptidyl transferase (one of the proteins in the ribosome), peptide bonds are formed between the successive amino acids, thus adding progressively to the protein chain. These chemical events require energy from two additional high-energy phosphate bonds, making a total of four high-energy bonds used for each amino acid added to the protein chain. Thus, the synthesis of proteins is one of the most energy-consuming processes of the cell.

Peptide Linkage. The successive amino acids in the protein chain combine with one another according to the typical reaction:

nh2 o i ii

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