A layman calls for help!

[Keith Robison]

cu630 at cleveland.Freenet.Edu (Gustave Rabson) writes:

>...There are 64 (4 cubed) permutations
>of 4 bases taken 3 at a time, but only 20 combinations.
>That is, if we consider two words to be the same if they
>consist of the same letters in any order there are
>only 20 combinations of the 4 letters. This would fit
>very well with 20 Amino Acids. So my question is
>how firmly established is it that combinations
>like GGU and GUG are different? What about mirror
>images, i.e. GCU and UCG?
>Thanks for your indulgence.

VERY firmly.  Also, remember that you need 20 amino acids
PLUS stop.  I suggest that you find a copy of Molecular Biology
of the Cell (by Alberts), Genes (by Lewin), or a similar textbook
(this is a good time to look for them -- students unloading them
enmass at term's end).  Most such books have detailed explanations
as to how the code was cracked, which I think you will find interesting.

Have fun!


Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

robison at biosun.harvard.edu