Unit 12: Cell Signaling

Question 1

what are extracellular signal molecules?

Answer 1

any molecule outside cell that elicits a cellular response when bound to a receptor

Question 2

what is endocrine signaling?

Answer 2

signals circulated through the bloodstream (animals) or sap (plants)

Question 3

what are signals produced by endocrine signaling called?

Answer 3

hormones

Question 4

what is paracrine signaling?

Answer 4

signal molecules that diffuse locally through extracellular fluid and act on nearby cells

Question 5

what is an example of molecules that undergo paracrine signalling?

Answer 5

molecules that control inflammation

Question 6

what is autocrine signaling?

Answer 6

when a cell responds to signals they produced themselves.

Question 7

what is an example of a cell that undergoes autocrine signaling?

Answer 7

cancer cells respond to their own growth

Question 8

what is neuronal signaling?

Answer 8

neurons way of signaling very specifically very fast through direct, private lines

Question 9

what is contact dependent signaling?

Answer 9

when cells make direct contact with signal and receptor molecules in plasma membrane

Question 10

describe the selectivity of receptors.

Answer 10

receptors only respond to one type of signal

Question 11

what are cell surface receptors?

Answer 11

receptors that bind extracellular signals

Question 12

what type of signal do cell surface receptors bind?

Answer 12

signals that are too large/hydrophilic to cross the membrane

Question 13

what are intracellular receptors?

Answer 13

receptors that bind to signals that pass through the plasma membrane

Question 14

what type of signal do intracellular receptors bind?

Answer 14

signals that are small and hydrophobic enough to cross the plasma membrane

Question 15

what type of proteins have an effect on cell behaviour?

Answer 15

effector proteins

Question 16

can one signal cause different effects? how?

Answer 16

yes bc its effect depends on which receptor it binds.

Question 17

describe how acetylcholine’s effect changes in heart cells and salivary glands.

Answer 17

• decreases heart rate if binds to heart cell
• causes salivary glands to release components of saliva if it binds

Question 18

how fast does muscle cell contraction occur?

Answer 18

milliseconds

Question 19

how can cell response be fast?

Answer 19

if there are proteins in cell waiting for signal

Question 20

how can cell response be slow?

Answer 20

if new proteins have to be synthesized/gene expression is changed

Question 21

describe the general intracellular signaling pathway

Answer 21

1. recognition of an extracellular signaling molecule and relay of signal across membrane
2. message is passed from one signaling molecule to the next
3. target molecule is reached and we get our target response

Question 22

how do phosphorylation molecular switches work?

Answer 22

protein kinase will attach phosphate to switch protein turning it on, protein phosphatase will remove phosphate, turning switch off.

Question 23

describe the molecular switch phosphorylation cascade

Answer 23

as one switch is phosphorylated, it will phosphorylate the next and so on.

Question 24

how do GTP-binding molecular switches work?

Answer 24

GTP bound = switch on
hydrolyzing GTP = GDP
GDP = switch off

Question 25

what are ion channel coupled receptors?

Answer 25

receptors that change permeability of membrane to specific ions which changes membrane potential (opens due to signal)

Question 26

what are G-protein-coupled receptors?

Answer 26

activate GTP-binding proteins to interact w an enzyme/ion channel to initiate an intracellular signaling cascade

Question 27

describe the general pathway of a signal reaching a G-coupled protein receptor.

Answer 27

1. signal binds receptor 2. signal passed to cytosolic g-protein 3. g-proteins turns an enzyme in the membrane on/off

Question 28

how many subunit does a G-protein have? what are they?

Answer 28

3! a, B, y

Question 29

which G-protein subunits are bound to fatty acid tails?

Answer 29

a, y

Question 30

describe a G-protein in an unstimulated state

Answer 30

the a subunit has a GDP bound

Question 31

how does a G-protein in its active state.

Answer 31

the GDP in the a subunit gets phosphorylated to become GTP

Question 32

why do G-proteins break apart?

Answer 32

subunits break apart to relay message to other molecules

Question 33

what does the a subunit contain that turns the G-protein from an active to an inactive state.

Answer 33

a GTPase that hydrolyzes GTP back to GDP

Question 34

how does cholera change the G-protein?

Answer 34

modifies the a-subunit so that the GTP cannot get hydrolyzed, locking the G-protein in its active state.

Question 35

how do control gated ion channels in heart pacemaker cells affect heart rate?

Answer 35

G-protein binds to the K+ channel, opening it, allowing an influx of K+ into the cell, slowing heart rate

Question 36

what are considered "first messengers"

Answer 36

the initial signals that activate the enzymes

Question 37

what are considered "second messengers"

Answer 37

the small molecules produced by the target enzymes of the first messengers

Question 38

what are some common second messengers?

Answer 38

cAMP, diacylglycerol, inositol triphosphate

Question 39

what is the function of AMP phosphodiesterase?

Answer 39

conversion of cAMP to AMP

Question 40

how does caffeine affect the levels of cAMP in the cell?

Answer 40

blocks the activity of AMP phosphodiesterase, keeping concentration of cAMP high

Question 41

what does AMP activate? what does it do?

Answer 41

cylic-AMP-dependant-protein kinase (PKA). phosphorylates intracellular proteins

Question 42

what are the cell responses we get from the breakdown of glucose (activation of glycogen phosphorylases)?

Answer 42

- increased heart rate - glycogen breakdown - fat breakdown - cortisol secretion

Question 43

what are enzyme coupled receptors?

Answer 43

receptors that act as/associate with enzymes to activate intracellular signaling pathways

Question 44

describe how receptor tyrosine kinases (RTKs) transmit signals.

Answer 44

1. extracellular signal causes two RTKs to dimerize 2. this close proximity causes kinase domains to activate and phosphorylate each other on tyrosines 3. each phosphorylated tyrosine serves as a docking site for other proteins 4. signaling proteins bind docking proteins forming a bimolecular condensate 5. signal moves down several routes simultaneously due to all of these proteins bound

Question 45

how can signals transduced by the RTK be terminated?

Answer 45

- tyrosine phosphatase removing phosphates OR - signal terminated by endocytosis causing destruction of the RTK

Question 46

is signal transduction a linear process?

Answer 46

no!