Proteins are naturally occurring polymers formed by

Chapter , Problem 12.86

(choose chapter or problem)

Proteins are naturally occurring polymers formed by condensation reactions of amino acids, which have the general structure H N C H R O C O H H In this structure, R represents H, CH3, or another group of atoms; there are 20 different natural amino acids, and each has one of 20 different R groups. (a) Draw the general structure of a protein formed by condensation polymerization of the generic amino acid shown here. (b) When only a few amino acids react to make a chain, the product is called a peptide rather than a protein; only when there are 50 amino acids or more in the chain would the molecule be called a protein. For three amino acids (distinguished by having three different R groups, R1, R2, and R3), draw the peptide that results from their condensation reactions. (c) The order in which the R groups exist in a peptide or protein has a huge influence on its biological activity. To distinguish different peptides and proteins, chemists call the first amino acid the one at the N terminus and the last one the one at the C terminus. From your drawing in part (b) you should be able to figure out what N terminus and C terminus mean. How many different peptides can be made from your three different amino acids?