Chapter 4 Flashcards
active site
Region on the surface of an enzyme that binds to a substrate
molecule and catalyzes its chemical transformation.
allosteric
Describes a protein that can exist in multiple conformations
depending on the binding of a molecule (ligand) at a
site other than the catalytic site; such changes from one
conformation to another often alter the protein’s activity or
ligand affinity.
α-helix
Folding pattern, common in many proteins, in which a
single polypeptide chain twists around itself to form a rigid
cylinder stabilized by hydrogen bonds between every fourth
amino acid.
amino acid sequence
The order of the amino acid subunits in a protein chain.
Sometimes called the primary structure of a protein.
antibody
Protein produced by B lymphocytes in response to a foreign
molecule or invading organism. Binds to the foreign
molecule or cell extremely tightly, thereby inactivating it or
marking it for destruction.
antigen
Molecule or fragment of a molecule that is recognized by
an antibody.
β-sheet
Folding pattern found in many proteins in which neighboring regions of the polypeptide chain associate side-by-side with each other through hydrogen bonds to give a rigid, flattened structure.
binding site
Region on the surface of a protein, typically a cavity or
groove, that interacts with another molecule (a ligand)
through the formation of multiple noncovalent bonds.
C-terminus
The end of a polypeptide chain that carries a free carboxyl
group (–COOH).
coenzyme
Small molecule that binds tightly to an enzyme and helps it
to catalyze a reaction
coiled-coil
Stable, rodlike protein structure formed when two or more
α helices twist repeatedly around each other.
conformation
Precise, three-dimensional shape of a protein or other
macromolecule, based on the spatial location of its atoms
in relation to one another
disulfide bond
Covalent cross-link formed between the sulfhydryl groups
on two cysteine side chains; often used to reinforce a
secreted protein’s structure or to join two different proteins
together.
enzyme
A protein that catalyzes a specific chemical reaction.
feedback inhibition
A form of metabolic control in which the end product of
a chain of enzymatic reactions reduces the activity of an
enzyme early in the pathway.
GTP-binding protein
Intracellular signaling protein whose activity is determined
by its association with either GTP or GDP. Includes both
trimeric G proteins and monomeric GTPases, such as Ras.
ligand
General term for a small molecule that binds to a specific
site on a macromolecule.
Michaelis constant (Km)
The concentration of substrate at which an enzyme works
at half its maximum velocity; serves as a measure of how
tightly the substrate is bound
motor protein
Protein such as myosin or kinesin that uses energy derived
from the hydrolysis of a tightly bound ATP molecule to
propel itself along a protein filament or polymeric molecule.
N-terminus
The end of a polypeptide chain that carries a free α-amino
group.
peptide bond
Covalent chemical bond between the
carbonyl group of one amino acid and the
amino group of a second amino acid. (See
Panel 2–6, pp. 76–77.)
polypeptide, polypeptide chain
Linear polymer composed of multiple amino acids. Proteins
are composed of one or more long polypeptide chains.
polypeptide backbone
Repeating sequence of the atoms (–N–C–C–) that form the core of a protein molecule and to which the amino acid side
chains are attached.
primary structure
The amino acid sequence of a protein.
protein domain
Segment of a polypeptide chain that can fold into a compact,
stable structure and that often carries out a specific function.
protein kinase
Enzyme that catalyzes the transfer of a phosphate group
from ATP to a specific amino acid side chain on a target
protein.
protein kinase
Enzyme that catalyzes the transfer of a phosphate group
from ATP to a specific amino acid side chain on a target
protein
protein machine
Assembly of protein molecules that operates as a
cooperative unit to perform a complex series of biological
activities, such as replicating DNA.
protein phosphatase
Enzyme that catalyzes the removal of a phosphate
group from a protein, often with high specificity for the
phosphorylated site.
protein phosphorylation
The covalent addition of a phosphate group to a side chain
of a protein, catalyzed by a protein kinase; serves as a form
of regulation that usually alters the activity or properties of
the target protein.
quaternary structure
Complete structure formed by multiple, interacting
polypeptide chains that form a larger protein molecule.
secondary structure
Regular local folding pattern of a polymeric molecule. In
proteins, it refers to α helices and β sheets.
side chain
Portion of an amino acid not involved in forming peptide
bonds; its chemical identity gives each amino acid unique
properties.
tertiary structure
Complete three-dimensional structure of a fully folded
protein.
transition state
Transient structure that forms during the course of a
chemical reaction; in this configuration, a molecule has the
highest free energy; it is no longer the substrate, but is not
yet the product.
turnover number
The maximum number of substrate molecules that an
enzyme can convert into product per second.
Vmax
The maximum rate of an enzymatic reaction, reached when
the active sites of all of the enzyme molecules in a sample
are fully occupied by substrate.
