Lecture 6

Question 1

Cell signaling pathways can be exceedingly complex, with multiple signals triggering pathways acting through common – or through separate –.

Answer 1

intermediates

Question 2

The ability of different signaling pathways to respond to distinct signals allows – of signaling that fine-tunes cell responses

Answer 2

integration

Question 3

– of signals can determine different cell fates

Answer 3

Combinatorial integration

Question 4

– is the basis of intercellular communication

Answer 4

Signal transduction

Question 5

Within an organism signals released by one cell act to trigger signal transduction in target cells which express the –

Answer 5

signal receptor.

Question 6

long range signaling can occur over long distances by transport of the signal through the bloodstream to distant targets.

Answer 6

endocrine signaling

Question 7

insulin is an example of – signaling

Answer 7

endocrine

Question 8

short range signaling to cells in the local vicinity of the signal producing cells. Examples include neurotransmitter release, and somatostatin releas

Answer 8

paracrine signaling

Question 9

released signal acts on the releasing cell. – by growth factors is a characteristic of many tumor cells

Answer 9

Autocrine signaling

Question 10

signals attached to the plasma membrane directly bind receptors on adjacent cells. (e.g. T signaling in immune system where an antigen is displayed on the surface of an antigen-presenting cell binds to the T-cell antigen receptor.)

Answer 10

Plasma membrane-associated protein signaling

Question 11

In the context of receptor binding, the signal is called a –

Answer 11

ligand

Question 12

The ligand binds to a specific site on the – domain of the receptor.

Answer 12

extracellular

Question 13

Ligand binding causes a – in the receptor that triggers the signal transduction pathway

Answer 13

conformational change

Question 14

Ligands and receptors are usually present at very low concentrations so binding must be tight (high affinity) AND –

Answer 14

specific

Question 15

Ligand binding assays allow determination of the – (often expressed as a dissociation constant, or Kd) and the number of receptors per cell

Answer 15

ligand-receptor affinity

Question 16

Known concentrations of ligand are added to cells and the amount – to the cells is determined.

Answer 16

bound

Question 17

Because there is a defined number of receptors in each cell, binding increases until all the receptors are occupied – this is the –

Answer 17

saturation binding level.

Question 18

the ligand concentration where the amount of ligand bound is half of the saturation level.

Answer 18

Kd

Question 19

The saturation level can be used to calculate the number of –per cell.

Answer 19

receptors

Question 20

Maximal physiological response to an external signal usually occurs when only – are occupied by ligand.

Answer 20

a fraction of the receptors

Question 21

three major classes of signaling receptors

Answer 21

ion channel, G protein coupled, enzyme linked receptors

Question 22

ion channel receptors (neurotransmitters) ligand binding causes channel opening
and –

Answer 22

ion flux

Question 23

G protein coupled receptors (GPCR) (e.g. beta adrenergic receptors for epinephrine): Ligand
binding activates a G-protein which in turn activates or inhibits an enzyme that generates a
specific –

Answer 23

second messenger.

Question 24

Receptor associated with separate enzyme (e.g. interferon receptor): Ligand-binding
causes – of the receptor and activation of cytosolic protein tyrosine or
serine/threonine kinases (phosphorylate tyrosine or serine/threonine in target protein).

Answer 24

dimerization

Question 25

Receptor with intrinsic enzyme (e.g. EGF receptor): Ligand-binding activates tyrosine
kinase activity within –

Answer 25

receptor cytoplasmic domain.

Question 26

molecule that binds to a receptor and activates signal transduction

Answer 26

agonist

Question 27

Antagonist: molecule that binds to a receptor and prevents activation by the normal ligand,
often by – to the same site on the receptor

Answer 27

competing for binding

Question 28

Activation of signaling pathways can lead to two types of responses.

Answer 28

rapid or persistent response

Question 29

rapid response involves alterations in – in the cytoplasm.

Answer 29

existing proteins

Question 30

persistent responses involve changes in – requires signaling

Answer 30

gene expression

Question 31

Classes of molecules that play key roles in signal

transduction: protein kinases,– and secondary messengers

Answer 31

GTPase switch proteins

Question 32

Ligand binding to receptors often leads to
activation of an intracellular protein kinase,
which – amino acids (hydroxyl
groups on serine, threonine, tyrosine) on target
proteins.

Answer 32

phosphorylates

Question 33

T/F: Depending on the particular target
protein, phosphorylation can activate OR
inactive the target.

Answer 33

true

Question 34

In the case of signaling GTPase
switch proteins, – are important in converting the
inactive GDP bound form to the active GTP
bound form.

Answer 34

guanine nucleotide exchange

factors (GEFs)

Question 35

– stimulate the intrinsic GTPase activity

of the GTPase switch protein, promoting inactivation

Answer 35

GTPase-activating proteins

GAPs

Question 36

Nonprotein, low-molecular-weight intracellular signaling molecules that regulate activities of
enzymes and nonenzymatic proteins in signaling pathways.

Answer 36

second messengers

Question 37

Once activated, cells have mechanisms to– signaling to prevent overstimulation.

Answer 37

dampen or inactive

Question 38

The receptor or components of the signaling pathway can be inhibited in several ways.

Answer 38

receptor inactivation, signaling protein inactivation, production of inhibitory protein, endocytosis, lysosomal degradation

Question 39

feedback regulation
from-- (such as
phosphorylation by an activated kinase) can
prevent receptor from engaging signaling
pathway

Answer 39

an activated signaling component

Question 40

Signaling protein inactivation: inactivation of
protein in signaling pathway – (such as phosphorylation or GTPase
activity)

Answer 40

downstream of

receptor

Question 41

Production of inhibitory protein: signaling
pathway activates an inhibitory protein that
blocks pathway (– feedback)

Answer 41

negative

Question 42

Endocytosis (by clathrin-coated vesicles) removes–,

leading to dissociation of the ligand and inactivation of the receptor.

Answer 42

receptors from the cell surface

Question 43

The receptor can
be recycled from endosomes to the cell surface,
a form of short term “–”

Answer 43

desensitization

Question 44

the receptor (and ligand) can be
transported to a lysosome where both are
degraded. This is called “–” and
results in longer term desensitization.

Answer 44

down-regulation