Chapter 16

Question 1

adaptation

Answer 1

Adjustment of sensitivity following repeated stimulation;
allows a cell or organism to register small changes in a
signal despite a high background level of stimulation.

Question 2

adenylyl cyclase

Answer 2

Enzyme that catalyzes the formation of cyclic AMP from
ATP; an important component in some intracellular
signaling pathways.

Question 3

Ca2+/calmodulin-dependant protein kinase (CaM-kinase)

Answer 3

Enzyme that phosphorylates target proteins in response to
an increase in Ca2+ ion concentration through its interaction
with the Ca2+-binding protein calmodulin.

Question 4

cell signaling

Answer 4

The molecular mechanisms by which cells detect and
respond to external stimuli and send messages to other
cells.

Question 5

cyclic AMP

Answer 5

Small intracellular signaling molecule generated from
ATP in response to hormonal stimulation of cell-surface
receptors.

Question 6

Cyclic-AMP-dependant protein kinase (PKA)

Answer 6

Enzyme that phosphorylates target proteins in response to

a rise in intracellular cyclic AMP concentration.

Question 7

diacylglycerol (DAG)

Answer 7

Small messenger molecule produced by the cleavage
of membrane inositol phospholipids in response to
extracellular signals. Helps activate protein kinase C.

Question 8

enzyme-coupled receptor

Answer 8

Transmembrane protein that, when stimulated by the
binding of a ligand, activates an intracellular enzyme (either
a separate enzyme or part of the receptor itself).

Question 9

extracellular signal molecule

Answer 9

Complex network of polysaccharides (such as
glycosaminoglycans or cellulose) and proteins (such as
collagen) secreted by cells. A structural component of tissues
that also influences their development and physiology.

Question 10

G protein

Answer 10

A membrane-bound GTP-binding protein involved in
intracellular signaling; composed of three subunits, this
intermediary is usually activated by the binding of a
hormone or other ligand to a transmembrane receptor.

Question 11

G-protein-coupled receptor (GPCR)

Answer 11

Cell-surface receptor that associates with
an intracellular trimeric GTP-binding
protein (G protein) after activation by an
extracellular ligand. These receptors are
embedded in the membrane by seven
transmembrane α helices.

Question 12

GTP-binding protein

Answer 12

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 13

hormone

Answer 13

Extracellular signal molecule that is secreted and
transported via the bloodstream (in animals) or the sap (in
plants) to target tissues on which it exerts a specific effect.

Question 14

inositol 1,4,5-triphosphate (IP3)

Answer 14

Small intracellular signaling molecule that triggers the
release of Ca2+ from the endoplasmic reticulum into the
cytosol; produced when a signal molecule activates a
membrane-bound protein called phospholipase C.

Question 15

inositol phospholipid

Answer 15

Minor lipid component of plasma membranes that plays a
part in signal transduction in eukaryotic cells; cleavage yields
two small messenger molecules, IP3 and diacylglycerol.

Question 16

intracellular signaling pathway

Answer 16

A set of proteins and small-molecule second messengers
that interact with each other to relay a signal from the
cell membrane to its final destination in the cytoplasm or
nucleus.

Question 17

ion-channel-coupled receptor

Answer 17

Transmembrane receptor protein or
protein complex that opens in response to
the binding of a ligand to its external face,
allowing the passage of a specific inorganic
ion.

Question 18

local mediator

Answer 18

Secreted signal molecule that acts at a short range on

adjacent cells.

Question 19

molecular switch

Answer 19

Intracellular signaling protein that toggles between an

active and inactive state in response to receiving a signal.

Question 20

neurotransmitter

Answer 20

Small signaling molecule secreted by a nerve cell at a
synapse to transmit information to a postsynaptic cell.
Examples include acetylcholine, glutamate, GABA, and
glycine.

Question 21

nitric oxide (NO)

Answer 21

Locally acting gaseous signal molecule that diffuses
across cell membranes to affect the activity of intracellular
proteins.

Question 22

nuclear receptor

Answer 22

Protein inside a eukaryotic cell that, on binding to a signal
molecule, enters the nucleus and regulates transcription.

Question 23

phospholipase C

Answer 23

Enzyme associated with the plasma membrane that
generates two small messenger molecules in response to
activation.

Question 24

protein kinase

Answer 24

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

Question 25

protein kinase C

Answer 25

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

Question 26

protein phosphotase

Answer 26

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

Question 27

receptor

Answer 27

Protein that recognizes and responds to a specific signal

molecule

Question 28

receptor tyrosine kinase (RTK)

Answer 28

Enzyme-coupled receptor in which the 
intracellular domain has a tyrosine kinase 
activity, which is activated by ligand 
binding to the receptor’s extracellular 
domain.

Question 29

serine/threonine kinase

Answer 29

Enzyme that phosphorylates target proteins on serines or

threonines.

Question 30

signal transduction

Answer 30

Conversion of an impulse or stimulus from one physical or
chemical form to another. In cell biology, the process by
which a cell responds to an extracellular signal.

Question 31

tyrosine kinase

Answer 31

Enzyme that phosphorylates target proteins on tyrosines.