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Name: Scott
Status: Student
Grade:  9-12
Location: TX
Country: United States
Date: May 2006


Question:
Hi, I am in 12th grade and studying biology. How is it that cells use ATP to harness energy and transfer energy? I understand by reading biology books that cells transfer a phosphate group off of the ATP molecule to another molecule to activate that other molecule. However, does it really work by transferring phosphate groups? For instance, say if two unactivated amino acids needed to be joined into a peptide bond. Wouldn't the enzyme just get two unactivated amino acids into an active site and a molecule of ATP at some other active site on the enzyme. Then the enzyme would hydrolyze ATP and thereby release heat. The enzyme would harness the heat released by the ATP hydrolysis and cram the two amino acids together to create a peptide bond.

Isn't this the way it works by the enzyme just going ahead and harnessing the heat released from the hydrolysis of ATP and not by transferring phosphate groups? Thereby creating the peptide bond.



Replies:
The way in which amino acids are activated to form a peptide bond is as follows. An enzyme named amionoacyl-tRNA synthetase transfers a phosphate group from ATP to the amino acid to form a short-lived complex called amino acid-AMP. This same enzyme then catalyzes the reaction of the acivated amino acid with it's specific tRNA molecule to form amino acid-tRNA + AMP. The amino group of the amino acid-tRNA conjugate then reacts with the -COOH group of the terminal amino acid of the nascent polypeptide being synthesized by enzymes that are a part of the ribosome.

Ron Baker, Ph.D.



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