Proteins are probably the most important class of biochemical
molecules, although of course lipids and carbohydrates are also
essential for life. Proteins are the basis for the major structural
components of animal and human tissue.
Proteins are natural polymer molecules consisting of amino
acid units. The number of amino acids in proteins may range
from two to several thousand. See Amino
Primary Protein Structure:
The primary protein structure is defined as the specific
sequence of amino acids in the protein. In order to function
properly, peptides and proteins must have the correct sequence
of amino acids. In the section on peptide
bonds, it was shown that a dipeptide consisting of two different
amino acids could have two different sequences as in the example
gly - ala or ala - gly.
Remember that as written left to right in gly-ala, the glycine
has the "free" amine terminal end and alanine has the
"free" carboxyl acid terminal end.
If three different amino acids (gly, ala, leu) are used to
make a tripeptide, how many different sequences are possible?
There are six possible sequences:
gly - ala - leu; gly - leu - ala; ala - gly - leu;
ala - leu - gly; leu - ala - gly; leu - gly - ala.
Review example: gly-ala-leu - Chime
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In the protein hormone insulin, 51 amino acids are found.
Using 51 amino acids there are 1.55 x 1066 different
possible sequences. Many other proteins contain many more amino
acids then insulin, but only the correct precise sequence is
produced by the body. The procedure used to synthesize the correct
sequence of amino acids in proteins is guided by the genetics
of DNA and RNA.