Because insulin exists, the doors are
open in figure 4.1, and the scientist has left. In all three cases, the door’s
combination is 7 amino acids long. The combination that opened each door is shown on the
screen. The combinations are very similar, but there are differences.
Figure 4.1: A Section of Insulin in Cat, Snake and Fish
Each of these 7 amino acid combinations corresponds to a section of the
real insulin protein in cat, snake and fish. The differences are important in determining
the allowed amino acids. The first amino acid is asparagine (asn) in rattlesnakes and
cats, but it is alanine in salmon; thus, both ala and asn are acceptable at position
number 1. At position 3, histidine (his) is found in both cats and fish, but arginine
(arg) is found in snakes; thus, both his and arg are acceptable at position number 3. In
figure 4.1, positions where more than one amino acid is allowed are represented by placing
the allowed amino acids in parenthesis; therefore, position 1 is represented by (asn, ala)
which means that either amino acid is fine at this position. From a comparison just like
this, it is possible to determine which amino acids are allowed at every position in the A
and B chains of insulin, and this will determine the amount of information contained in
insulin today.
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