Chapter 4

Question 1

active site

Answer 1

Region on the surface of an enzyme that binds to a substrate
molecule and catalyzes its chemical transformation.

Question 2

allosteric

Answer 2

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.

Question 3

α-helix

Answer 3

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.

Question 4

amino acid sequence

Answer 4

The order of the amino acid subunits in a protein chain.

Sometimes called the primary structure of a protein.

Question 5

antibody

Answer 5

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.

Question 6

antigen

Answer 6

Molecule or fragment of a molecule that is recognized by

an antibody.

Question 7

β-sheet

Answer 7

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.

Question 8

binding site

Answer 8

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.

Question 9

C-terminus

Answer 9

The end of a polypeptide chain that carries a free carboxyl

group (–COOH).

Question 10

coenzyme

Answer 10

Small molecule that binds tightly to an enzyme and helps it

to catalyze a reaction

Question 11

coiled-coil

Answer 11

Stable, rodlike protein structure formed when two or more

α helices twist repeatedly around each other.

Question 12

conformation

Answer 12

Precise, three-dimensional shape of a protein or other
macromolecule, based on the spatial location of its atoms
in relation to one another

Question 13

disulfide bond

Answer 13

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.

Question 14

enzyme

Answer 14

A protein that catalyzes a specific chemical reaction.

Question 15

feedback inhibition

Answer 15

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.

Question 16

GTP-binding protein

Answer 16

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.

Question 17

ligand

Answer 17

General term for a small molecule that binds to a specific

site on a macromolecule.

Question 18

Michaelis constant (Km)

Answer 18

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

Question 19

motor protein

Answer 19

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.

Question 20

N-terminus

Answer 20

The end of a polypeptide chain that carries a free α-amino

group.

Question 21

peptide bond

Answer 21

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.)

Question 22

polypeptide, polypeptide chain

Answer 22

Linear polymer composed of multiple amino acids. Proteins

are composed of one or more long polypeptide chains.

Question 23

polypeptide backbone

Answer 23

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.

Question 24

primary structure

Answer 24

The amino acid sequence of a protein.

Question 25

protein domain

Answer 25

Segment of a polypeptide chain that can fold into a compact,
stable structure and that often carries out a specific function.

Question 26

protein kinase

Answer 26

Enzyme that catalyzes the transfer of a phosphate group
from ATP to a specific amino acid side chain on a target
protein.

Question 27

protein kinase

Answer 27

Enzyme that catalyzes the transfer of a phosphate group
from ATP to a specific amino acid side chain on a target
protein

Question 28

protein machine

Answer 28

Assembly of protein molecules that operates as a
cooperative unit to perform a complex series of biological
activities, such as replicating DNA.

Question 29

protein phosphatase

Answer 29

Enzyme that catalyzes the removal of a phosphate
group from a protein, often with high specificity for the
phosphorylated site.

Question 30

protein phosphorylation

Answer 30

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.

Question 31

quaternary structure

Answer 31

Complete structure formed by multiple, interacting

polypeptide chains that form a larger protein molecule.

Question 32

secondary structure

Answer 32

Regular local folding pattern of a polymeric molecule. In

proteins, it refers to α helices and β sheets.

Question 33

side chain

Answer 33

Portion of an amino acid not involved in forming peptide
bonds; its chemical identity gives each amino acid unique
properties.

Question 34

tertiary structure

Answer 34

Complete three-dimensional structure of a fully folded

protein.

Question 35

transition state

Answer 35

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.

Question 36

turnover number

Answer 36

The maximum number of substrate molecules that an

enzyme can convert into product per second.

Question 37

Vmax

Answer 37

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.