Chapter 4 Flashcards

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1
Q

active site

A

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

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2
Q

allosteric

A

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.

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3
Q

α-helix

A

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.

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4
Q

amino acid sequence

A

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

Sometimes called the primary structure of a protein.

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5
Q

antibody

A

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.

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6
Q

antigen

A

Molecule or fragment of a molecule that is recognized by

an antibody.

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7
Q

β-sheet

A
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.
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8
Q

binding site

A

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.

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9
Q

C-terminus

A

The end of a polypeptide chain that carries a free carboxyl

group (–COOH).

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10
Q

coenzyme

A

Small molecule that binds tightly to an enzyme and helps it

to catalyze a reaction

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11
Q

coiled-coil

A

Stable, rodlike protein structure formed when two or more

α helices twist repeatedly around each other.

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12
Q

conformation

A

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

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13
Q

disulfide bond

A

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.

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14
Q

enzyme

A

A protein that catalyzes a specific chemical reaction.

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15
Q

feedback inhibition

A

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.

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16
Q

GTP-binding protein

A

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.

17
Q

ligand

A

General term for a small molecule that binds to a specific

site on a macromolecule.

18
Q

Michaelis constant (Km)

A

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

19
Q

motor protein

A

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.

20
Q

N-terminus

A

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

group.

21
Q

peptide bond

A

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.)

22
Q

polypeptide, polypeptide chain

A

Linear polymer composed of multiple amino acids. Proteins

are composed of one or more long polypeptide chains.

23
Q

polypeptide backbone

A

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.

24
Q

primary structure

A

The amino acid sequence of a protein.

25
Q

protein domain

A

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

26
Q

protein kinase

A

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

27
Q

protein kinase

A

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

28
Q

protein machine

A

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

29
Q

protein phosphatase

A

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

30
Q

protein phosphorylation

A

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.

31
Q

quaternary structure

A

Complete structure formed by multiple, interacting

polypeptide chains that form a larger protein molecule.

32
Q

secondary structure

A

Regular local folding pattern of a polymeric molecule. In

proteins, it refers to α helices and β sheets.

33
Q

side chain

A

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

34
Q

tertiary structure

A

Complete three-dimensional structure of a fully folded

protein.

35
Q

transition state

A

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.

36
Q

turnover number

A

The maximum number of substrate molecules that an

enzyme can convert into product per second.

37
Q

Vmax

A

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.