chap16

Question 1

Cells in multicellular organisms communicate through a huge variety of _.

Answer 1

extracellular chemical signals

Question 2

In animals, hormones are carried in the blood to distant target cells, but most other extracellular signal molecules act over only a short distance. Neighboring cells often communicate through _

Answer 2

direct cell-cell contact.

Question 3

For an extracellular signal molecule to influence a target cell it must interact with a _ on or in the target cell. Each _ protein recognizes a _ signal molecule.

Answer 3

receptor protein
receptor
particular

Question 4

Most extracellular signal molecules bind to cell-surface receptor proteins that _ the extracellular signal into different _ signals, which are usually organized into _ pathways.

Answer 4

convert (transduce)
intracellular
signaling

Question 5

There are three main classes of cell-surface receptors: (1) _, (2) _, and (3) _

Answer 5

ion- channel-coupled receptors
G-protein-coupled receptors (GPCRs)
enzyme-coupled receptors.

Question 6

GPCRs and enzyme-coupled receptors respond to extracellular signals by _, which, in turn, activate _ that _.

Answer 6

_
activating one or more intracellular signaling pathways
_
effector proteins
_
alter the behavior of the cell

Question 7

_ signaling pathways is as important as turning them on. Each activated component in a signaling pathway must be subsequently _ for the pathway to function again.

Answer 7

Turning off
inactivated or removed

Question 8

GPCRs activate _ called _ proteins; these act as _, transmitting the signal onward for a short period before switching _ by hydrolyzing their bound GTP to GDP.

Answer 8

trimeric GTP-binding proteins
G
molecular switches
themselves off

Question 9

G proteins directly regulate _ or _ in the plasma membrane. Some directly activate (or inactivate) the _, which increases (or decreases) the intracellular concentration of the second messenger molecule _; others directly activate the _, which generates the second messenger molecules _ and _.

Answer 9

ion channels
enzymes
enzyme adenylyl cyclase
cyclic AMP
enzyme phospholipase C
inositol trisphosphate (IP3)
diacylglycerol

Question 10

_ opens Ca2+ channels in the membrane of the endoplasmic reticulum, releasing a flood of free Ca2+ ions into the cytosol. The Ca2+ itself acts as a _, altering the activity of a wide range of _ proteins. These include calmodulin, which activates various target proteins such as _

Answer 10

IP3
second messenger
Ca2+-responsive
_
Ca2+/calmodulin-dependent protein kinases (CaM-kinases).
_

Question 11

A rise in cyclic AMP activates _, while Ca2+ and diacylglycerol in combination activate _.

Answer 11

protein kinase A (PKA)
protein kinase C (PKC)

Question 12

PKA, PKC, and CaM-kinases phosphorylate selected _ proteins on _ and _, thereby altering their activity. Different cell types contain _ sets of _ and are therefore affected in different ways.

Answer 12

signaling and effector
serines
threonines
different
signaling and effector proteins

Question 13

Enzyme-coupled receptors have intracellular protein domains that function as _ or are _. Many enzyme-coupled receptors are _, which _ themselves and select intracellular signaling proteins on _. The phosphotyrosines on RTKs then serve as _ for various _ proteins.

Answer 13

enzymes
associated with intracellular enzymes
receptor tyrosine kinases (RTKs)
phosphorylate
tyrosines
docking sites
intracellular signaling

Question 14

Most RTKs activate the monomeric _, which, in turn, activates a _ signaling module that helps relay the signal from the plasma membrane to the _.

Answer 14

GTPase Ras
three-protein MAP-kinase
nucleus

Question 15

Ras mutations stimulate _ by keeping Ras (and, consequently, the Ras–MAP kinase signaling pathway) constantly _ and are a common feature of many human _.

Answer 15

cell proliferation
active
cancers

Question 16

Some RTKs stimulate cell _ and cell _ by activating PI 3-kinase, which phosphorylates specific _ in the cytosolic leaflet of the plasma membrane lipid bilayer. This inositol _ creates lipid _ sites that attract specific signaling proteins from the cytosol, including the protein kinase Akt, which becomes active and relays the signal onward.

Answer 16

growth
survival
inositol phospholipids
phosphorylation
docking

Question 17

Other receptors, such as Notch, have a direct pathway to the _. When activated, part of the receptor migrates from the plasma membrane to the _, where it regulates the _

Answer 17

nucleus
nucleus
transcription of specific genes.

Question 18

Some _, such as steroid hormones and nitric oxide, are small or hydrophobic enough to cross the plasma membrane and activate _ proteins, which are usually either _ regulators or _.

Answer 18

extracellular signal molecules
intracellular
transcription
enzymes

Question 19

Plants, like animals, use enzyme-coupled cell-surface receptors to recognize the extracellular signal molecules that control their _ and _; these receptors often act by _ of specific genes.

Answer 19

growth
development
relieving the transcriptional repression

Question 20

Different intracellular signaling pathways _, enabling each cell type to produce the appropriate response to a combination of _. In the absence of such signals, most animal cells have been programmed to _

Answer 20

interact
extra-cellular signals
kill themselves by undergoing apoptosis.

Question 21

Animal cells use extracellular signal molecules to communicate with one another
in various ways:

Answer 21

endocrine signals
Paracrine signals
Neuronal signals
contact-dependent signaling

Question 22

Hormones produced in _ glands are secreted into the bloodstream and
are distributed widely throughout the body.

Answer 22

endocrine

Question 23

_ signals are released by cells into the extracellular fluid in their neighborhood and act locally.

Answer 23

Paracrine

Question 24

In contact-dependent signaling, a cell-surface-bound _ binds to a _ on an _ cell. Many of the same types of signal molecules are used for endocrine, paracrine, and neuronal signaling. The crucial differences lie in the _ and _ with which the signals are delivered to their targets.

Answer 24

signal molecule
receptor protein
adjacent
speed
selectivity

Question 25

responses—such as _—need not involve changes in gene expression and therefore occur more quickly

Answer 25

changes in cell movement, secretion, or metabolism

Question 26

Signaling molecules eventually interact with _, altering them to change the behavior of the cell in various ways.

Answer 26

specific effector proteins

Question 27

Intracellular signaling proteins can relay, amplify, integrate, distribute, and modulate via _.

Answer 27

feedback an incoming signal

Question 28

a receptor protein located on the cell surface _ an extracellular signal into an intracellular signal

Answer 28

transduces

Question 29

Note that some proteins in the pathway may be held in close proximity by a _, which allows them to be activated at a _ in the cell and with greater speed, efficiency, and selectivity

Answer 29

scaffold protein
specific location

Question 30

a downstream protein in a signaling pathway, protein Y, acts to _ the activity of the protein that activated it—a form of positive feedback.

Answer 30

increase

Question 31

Positive feedback loops can ignite an _ response, such as the activation of the proteins that trigger cell division

Answer 31

explosive

Question 32

In a simple example of negative feedback, protein Y _ the protein that activated it.

Answer 32

inhibits

Question 33

The activity of monomeric
GTPases is controlled by two types of
regulatory proteins. _ promote the
exchange of GDP for GTP, thereby switching the protein on. _ stimulate the hydrolysis of GTP to GDP, thereby switching the protein off.

Answer 33

Guanine nucleotide exchange factors (GEFs)
GTPase-activating proteins (GAPs)

Question 34

Two messenger molecules are produced when a membrane _ is hydrolyzed by activated _. _ diffuses through the cytosol and triggers the release of _from the ER by binding to and opening special _ channels in the ER membrane. The large electrochemical gradient for _ across this membrane causes _
to rush out of the ER and into the cytosol. _ remains in the plasma membrane and, together with _, helps activate the enzyme _, which is recruited from the cytosol to the cytosolic face of the plasma membrane (Movie 16.4). _ then phosphorylates
its own set of intracellular proteins, further propagating the signal.

Answer 34

inositol phospholipid
phospholipase C
Inositol 1,4,5-trisphosphate (IP3)
Ca2+
Ca2+
Ca2+
Ca2+
Diacylglycerol
Ca2+
protein kinase C (PKC)
PKC