Denniston, 8e
Glossary of Key Terms in Chapter Eighteen
-amino acids (18.2) the basic subunits of proteins; each is composed of an -carbon bonded to a
carboxylate group, a protonated amino group, a hydrogen atom, and a variable “R” group.
antibody (18.1) one of the specific proteins produced by cells of the immune system in response to
invasion by infectious agents.
antigen (18.1) any substance able to stimulate the immune system; they are usually proteins or large
carbohydrates.
coagulation (18.10) the process by which proteins in solution are denatured and aggregate with one
another to produce a solid.
complete protein (18.11) a protein source that contains all the essential and nonessential amino acids.
C-terminal amino acid (18.3) the amino acid at the end of the protein chain that has a free –CO2– group;
this is the last amino acid in a peptide.
defense proteins (18.1) proteins that defend the body against infectious diseases; antibodies are defense
proteins.
denaturation (18.10) the process by which the organized structure of a protein is disrupted resulting in a
completely disorganized, nonfunctional form of the protein.
enzyme (18.1) a protein that serves as a biological catalyst.
essential amino acid (18.11) an amino acid that cannot be synthesized by the body and must therefore be
supplied by the diet.
fibrous protein (18.5) a protein composed of peptides arranged in long sheets or fibers.
globular protein (18.6) a protein composed of polypeptide chains that are tightly folded into a compact
spherical shape.
glycoprotein (18.7) a protein with sugars as prosthetic groups; often these are receptors on the cell surface.
-helix (18.5) a right-handed coiled secondary structure maintained by hydrogen bonds between the
amide hydrogen of one amino acid and the carbonyl oxygen of an amino acid four residues away.
heme group (18.9) the chemical group found in hemoglobin and myoglobin that is responsible for the
ability to carry oxygen.
hemoglobin (18.9) the major protein component of red blood cells; the function of this red, ironcontaining protein is transport of oxygen.
hydrophilic amino acid (18.2) “water loving,” one of the polar or ionic amino acids that has a high
affinity for water.
hydrophobic amino acid (18.2) “water fearing,” a nonpolar amino acid that prefers contact with other
nonpolar amino acids over contact with water.
incomplete protein (18.11) a protein source that does not contain all of the essential and nonessential
amino acids.
isoelectric point (18.10) the pH at which the protein has an equal number of positive and negative
charges and therefore has an overall net charge of zero.
-keratin (18.5) fibrous proteins that form the covering of most land animals; they are major components
of fur, skin, beaks, and nails.
movement protein (18.1) a protein involved in any aspect of movement in an organism, for instance, actin
and myosin in muscle tissue and flagellin that composes bacterial flagella.
myoglobin (18.9) the oxygen storage protein found in muscle.
nonessential amino acid (18.11) an amino acid that can be synthesized by the body.
N-terminal amino acid (18.3) the amino acid at the end of a protein chain that has a free -N+H3 group;
this is the first amino acid of a peptide.
nutrient protein (18.1) a protein that serves as a source of amino acids for embryos or fetuses.
peptide bond (18.3) the covalent linkage between two amino acids in a peptide chain; an amide formed
by a condensation reaction between two amino acids.
-pleated sheet (18.5) a common secondary structure that resembles the pleats of an oriental fan.
primary structure (of a protein) (18.4) the sequence of amino acids in a protein; this is determined by
the genetic information of the gene for each protein.
prosthetic group (18.7) a nonprotein group that is attached to a protein and is essential to the biological
activity of that protein; often a complex organic compound.
protein (Intro) a macromolecule whose primary structure is a linear sequence of -amino acids and
whose final structure results from folding of the chain into a specific three-dimensional structure; they
have many functions in the organism, including serving as catalysts, structural components, and
nutritional elements.
quaternary structure (of a protein) (18.7) aggregation of two or more globular proteins to form a
functional protein.
regulatory protein (18.1) a protein that controls cell functions such as metabolism and reproduction.
secondary structure (of a protein) (18.5) folding of the primary structure of a protein into an -helix or
a -pleated sheet; the forces that maintain the folding are hydrogen bonds between the amide hydrogen
and the carbonyl oxygen of the peptide bond.
sickle cell anemia (18.9) a human genetic disease resulting from inheriting mutant hemoglobin genes
from both parents.
structural protein (18.1) a protein that provides mechanical support for large plants and animals.
tertiary structure (of a protein) (18.6) the globular, three-dimensional structure of a protein that results
from folding the regions of secondary structure; this folding occurs spontaneously as a result of
interactions of the side chains or R groups of the amino acids.
transport protein (18.1) a protein that transports materials across the cell membrane or soluble proteins,
such as hemoglobin, that carry substances through the body.