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Name: Angelica
Status: Student
Grade:  9-12
Location: VA
Country: United States
Date: September 2005

There are 64 amino acids overall but why does only 20 of them exist in humans?

There are actually many more than 64 amino acids, because the class of substances "amino acids" only requires one carboxyl group and one amine group. The presence of other groups is not excluded, and some of the group of 20 do contain sulfur. I don't think anyone knows why the "essential amino acids" are 20 in number. Even given the number, no one knows why these amino acids are "left handed", that is plane polarized light is rotated in only one direction. There are many unanswered questions in molecular biology.

Vince Calder

There are only 20 amino acids in nature, not 64. There are 64 different triplet codons in DNA and RNA (4 x 4 x4). A doublet code could only code for 4 x 4 = 16 codons. 64 is the minimum number of codons required to code for 20 amino acids.

Ron Baker, Ph.D.

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