The folding and coiling patterns of a protein often affect its biological activity, for
instance, its effectiveness as an enzyme. Forces such as heat and ionic environment
can alter the pattern of folding and coiling, causing the enzyme to become inactive, or
denatured.
Proteins make up more than 50% of the dry weight of animals and bacteria. They
perform many important functions in living organisms, a few of which are indicated in
Table 28-7. Each protein carries out a specific biochemical function. Each is a polypep-
tide with its own unique sequenceof amino acids. The amino acid sequence of a protein
determines exactly how it folds up in a three-dimensional conformation and how it
performs its precise biochemical task.
28-9 Polypeptides and Proteins 1133A model of the protein
ribonuclease A in stereoview.
The different colors represent
regions within the folding and
coiling patterns.
A “ribbon” model of the protein calmodulin. In this
type of model, the ribbon represents the
polypeptide chain. This protein coordinates with
Ca^2 ions (white spheres) and aids in transporting
them in living systems.