Denaturation is the process of changing the structures of proteins which allows for them to be digested. The protein is still intact and the amino acids are still linked together, but the coiling and shape of the protein is just loosened or modified so that the protein is no longer functional. Usually classified as a noncovalent change in the structure of a protein. “Denaturation of proteins involves the disruption and possible destruction of both the secondary and tertiary structures. Since denaturation reactions are not strong enough to break the peptide bonds, the primary structure (sequence of amino acids) remains the same after a denaturation process. Denaturation disrupts the normal alpha-helix and beta sheets in a protein and uncoils it into a random shape.” (Elmhurst) The visual thought of “uncoiling” is really what sets this apart in my mind. Digestion breaks bonds, denaturation uncoils them. “Denaturation is defined as a major change from the original native state without alteration of the molecule's primary structure, i.e., without cleavage of any of the primary chemical bonds that link one amino acid to another.” (Online Encyclopedia) Denaturation usually renders a protein biologically inactive because of the separation of the strands.
Characteristic Changes:
- Loss of Solubility
- Increased Proteolysis
- Loss of Biological Activity
- Change of Volume (depends on temperature)
Denaturation of proteins can be caused by heat (thermal denaturation), alkali or acid treatments (pH denaturation) by something like adding lemon juice to milk makes the proteins curdle, or metals (cooking in a cast iron pot). This importance of this process is it prepares the protein to be moved along into digestion. Digestion breaks down the proteins – denaturation does not.
Examples of denaturation:
“A classic example of denaturing in proteins comes from egg whites, which are largely egg albumins in water. Fresh from the eggs, egg whites are transparent and liquid. But by cooking they are turned opaque and white, and form an interconnected solid mass. The same transformation can be effected with a denaturing chemical. Pouring egg whites into a beaker of acetone will also turn egg whites opaque and solid. The skin which forms on curdled milk is another common example of denatured protein.
An example of reversible denaturing in proteins is the modern permanent wave technique for curling or straightening hair.” (Wikipedia) Denaturation of nucleic acids was thought to be irreversible until 1961.