26.2. Amino Acids and Proteins http://www.ck12.org
Inhibitors
Aninhibitoris a molecule that interferes with the function of an enzyme, either slowing or stopping the chemical
reaction catalyzed by that enzyme. Inhibitors can work in a variety of ways, but one of the most common is illustrated
below (Figure26.15).
FIGURE 26.15
A competitive inhibitor is a molecule that
binds to the active site of an enzyme with-
out reacting, thus preventing the substrate
from binding.The inhibitor binds competitively at the active site and blocks the substrate from binding. Since no reaction occurs
with the inhibitor, the enzyme is prevented from catalyzing the reaction. Cyanide is a potent poison that acts
as a competitive inhibitor. It binds to the active site of the enzymecytochrome c oxidaseand interrupts cellular
respiration. The binding of the cyanide to the enzyme is almost completely irreversible, and the affected organism
dies quickly.
Cofactors
Some enzymes require the presence of non-protein molecules or ions in order to function properly; these additional
components are referred to as cofactors. Cofactors can be inorganic metal ions or small organic molecules. Many
vitamins, such as the B vitamins, act as cofactors. Some metal ions that function as cofactors for various enzymes
include zinc, magnesium, potassium, and iron.
Lesson Summary
- Amino acids are the building blocks of proteins. An amino acid has a carboxyl group, an amino group, and a
variable side chain all covalently bonded to a central carbon atom. There are twenty fundamental amino acids,
each with a unique side chain, that are used as the building blocks of proteins in living organisms. - Amino acids can undergo a condensation reaction in which the carbon atom of the carboxyl group of one
amino acid bonds to the amino nitrogen atom of another amino acid. The result is called a peptide bond.
Polypeptides and proteins are long strings of amino acids. - Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. The structure and function
of a protein is ultimately governed by its amino acid sequence.