Unit 7

Question 1

//Cells communicate by means of

Answer 1

extracellular signaling molecules

Question 2

Signaling molecules are synthesized and released by

Answer 2

signaling cells

Question 3

Signaling molecules are synthesized and released by signaling cells and produce

Answer 3

a specific response only in target cells that have receptors for the signaling molecules.

Question 4

Signal transduction:

Answer 4

the process of converting an extracellular signal (signaling molecule A) into an intracellular signal (signaling molecule
B) in a target cell.

Question 5

The intracellular signal initiates a series of intracellular reactions that regulate (6):

Answer 5

(1) Transcription
(2) Survival
(3) Protein synthesis
(4) Movement
(5) Cell death
(6) Metabolic changes

Question 6

What are the six steps in signalling:

Answer 6

1. SYNTHESIS of the signaling molecule by the signaling cell
2. RELEASE of the signaling molecule by the signaling cell
   3.TRANSPORT of the signaling molecule to the target cell
3. DETECTION of the signal by a specific receptor protein
4. a CHANGE in cellular metabolism, function, or development triggered by the receptor-signaling molecule complex
5. REMOVAL of the signaling molecule ,which terminates the cellular response

Question 7

Signaling can be classified into 4 types that act over short or long distances:

Answer 7

1. Autocrine
2. Paracrine
3. Endocrine
4. Contact-dependent

Question 8

In autocrine signaling (1/4 types signalling), cells respond to

Answer 8

signaling molecules that they themselves release.

Question 9

This type of signaling is particularly common in cancer cells, which overproduce and release growth factors that stimulate inappropriate, unregulated growth and division of themselves, leading to cancer development

Answer 9

autocrine signaling

Question 10

In paracrine signaling (1/4 types of signaling) …

Answer 10

the signaling molecules released by a signaling cell into the extracellular medium act LOCALLY to affect target cells in CLOSE PROXIMITY to the signaling cell

Question 11

In endocrine signalling (1/4 types of signalling) , the signalling molecules are called __ and act on __

Answer 11

in endocrine signalling, the signalling molecules are called HORMONES and act on target cells DISTANT from their site of synthesis by endocrine cells

Question 12

Hormones produced in endocrine cells are secreted into__ and can be __

Answer 12

Hormones produced in endocrine cells are secreted into the bloodstream and can be distributed widely throughout the body.

Question 13

In contact-dependent signaling (1/4 types of signalling), a ___ in the plasma membrane of the signaling cell binds to a receptor molecule embedded in the plasma membrane of the target cell.

Answer 13

membrane-anchored signal

Question 14

In contact-dependent signaling, a membrane-anchored signal __

Answer 14

in the plasma membrane of the signaling cell binds to a receptor molecule embedded in the plasma membrane of the target cell.

Question 15

In contact-dependent signaling, a membrane-anchored signal in the plasma membrane of the signaling cell binds to a receptor molecule embedded in the plasma membrane of the target cell. This requires __

Answer 15

cells to be in direct membrane-to-membrane contact with each other

Question 16

contact dependant signaling does not require:

Answer 16

the release of a signaling molecule.

Question 17

What type of signalling does not require the release of a signalling molecule?

Answer 17

contact dependant signalling

Question 18

true/false: in extracellular signalling, the signalling molecule is the signal?

Answer 18

The extracellular signaling molecule alone is not the signal. The signal depends on how the target cell interprets the signaling molecule, which is dictated by intracellular signaling pathways.
signal is the “process”

Question 19

in extracellular signalling, the signalling molecule alone is not the signal. The signal depends on:

Answer 19

how the target cell interprets the signaling molecule, which is dictated by intracellular signaling pathways.

Question 21

Intracellular signaling pathways: Signaling pathways consist of

Answer 21

a series of proteins and/or second messengers.

Question 22

Intracellular signaling pathways:Each protein in a pathway

Answer 22

alters the conformation or activity of the next
protein.

Question 23

Intracellular Signaling Pathways: In some cases the intracellular signaling molecule can be __ . These are referred to as ___.

Answer 23

In some cases the intracellular signaling molecule can be a small molecule (e.g. cAMP, Ca2+). These are referred to as second messengers.

Question 24

in intracellular signaling pathways: protein conformation is usually altered by:

Answer 24

phosphorylation

Question 25

in regards to intracellular signaling pathways (more specifically,protein conformation), kinases do what?

Answer 25

add phosphate

Question 26

in regards to intracellular signaling pathways (more specifically,protein conformation), phosphotases do what?

Answer 26

remove a phosphate

Question 27

Intracellular signaling pathways: Target proteins ultimately __

Answer 27

receive a message to alter cell activity.

Question 28

When signaling is mediated by __, upon activation of the signaling cascade there are __ types of molecular switches:

Answer 28

When signaling is mediated by proteins, upon activation of the signaling cascade there are four types of molecular switches

Question 29

When signaling is mediated by proteins, upon activation of the signaling cascade there are four types of molecular switches:

Answer 29

1. phosphorylation-dephosphorylation 2. GTP binding (e.g. G-protein-coupled receptor) 3. assembly-disassembly of protein complexes 4. proteolysis (irreversible)

Question 30

Protein phosphorylation can __

Answer 30

change protein behaviour in different ways

Question 31

Molecular switch 1/4: phosphorylation-dephosphorylation: Protein phosphorylation can change protein behaviour in different ways (4):

Answer 31

1. It can activate or inactivate an enzyme. 2. It can promote or interfere with protein-protein interactions. 3. It can change the subcellular location of the protein. 4. It can trigger protein degradation

Question 32

a kinase tends to __ a signal

Answer 32

activate

Question 33

a phosphatase tends to __ a signal.

Answer 33

inactivate

Question 34

A GTP-binding protein is active when bound to __

Answer 34

GTP

Question 35

A GTP-binding protein is inactive when bound to __

Answer 35

GDP

Question 36

In the absence of a signal, the GTP-binding protein is bound to

Answer 36

GDP

Question 37

A GTP-binding protein is active when bound to GTP and inactive when bound to GDP. In the absence of a signal, the GTP-binding protein is bound to GDP.Signals activate the release of __ and the subsequent binding to ___

Answer 37

Signals activate the release of GDP and the subsequent binding to GTP

Question 38

how do intracellular signaling proteins convert active form of GTP to GDP?

Answer 38

The GTPase activity of these intracellular signaling proteins hydrolyses the bound GTP to GDP and Pi, thus converting the active form back to the inactive form

Question 39

Many signal-transduction cascades contain:

Answer 39

multiprotein signaling complexes.

Question 40

Some proteins act as __ to bring other signaling molecules into proximity for sequential activation

Answer 40

scaffolds

Question 41

Some signaling proteins can interact with the activated receptor and

Answer 41

transmit the signal to downstream effector proteins

Question 42

Most interactions during signaling are mediated by specific _

Answer 42

protein domains

Question 43

Define protein domain:

Answer 43

stretches of amino acids that share some degree of similarity and can function independently of the entire protein.

Question 44

Some examples of protein interaction domains found in signaling molecules are (4):

Answer 44

(1) Src homology 2 (SH2) domains (2) Src homology 3 (SH3) domains (3) pleckstrin homology (PH) domains (4) phosphotyrosine-binding (PTB) domains

Question 45

Some signaling cascades are mediated by proteolysis where:

Answer 45

the intracellular portion of the receptor is cleaved and acts as a signaling molecule.

Question 46

Some signaling cascades are mediated by ___ where the intracellular portion of the receptor is cleaved and acts as a signaling molecule.

Answer 46

proteolysis

Question 47

SH2 domain –

Answer 47

binds to phosphate in a particular sequence

Question 48

SH3 domain - binds to

Answer 48

proline-rich sequences

Question 49

PH domain binds to:

Answer 49

certain phosphoinositides

Question 50

PTB domain binds to:

Answer 50

phosphorylated tyrosine residues in a particular sequence

Question 51

In contrast to the other three molecular switches, this type of switch is not reversible:

Answer 51

proteolysis -> once the protein is cleaved it cannot be undone

Question 52

Molecular switch: phosphorylation can be reversed by a

Answer 52

phosphatase

Question 53

Molecular switch:GTP activation can be reversed by

Answer 53

GTP hydrolysis

Question 54

true or false: protein assembly can be undone:

Answer 54

true

Question 55

Intracellular signaling pathways The pathway can be thought of as a cascade of events. The cascade serves to (4):

Answer 55

1. RELAY THE SIGNAL and help spread it in the cell. 2. AMPLIFY THE SIGNAL such that a few extracellular molecules can provoke a large intracellular response. 3. INTEGRATE signals from other pathways before relaying them onward. 4. DISTRIBUTE THE SIGNAL to a number of different effector proteins evoking a complex response.

Question 56

Amplification of the epinephrine signal:

Answer 56

1 molecule of epinephrine leads to the production of 100x106 molecules of glucose-1-phosphate

Question 57

Extracellular signaling molecules fall into __ classes, corresponding to __

Answer 57

Extracellular signaling molecules fall into 2 classes, corresponding to 2 fundamentally different classes of receptors.

Question 58

1st class (largest) of extracellular signaling molecules:

Answer 58

- extracellular signaling molecules are too large and too hydrophilic to cross the plasma membrane - receptors are on the outer surface of the plasma membrane of the target cell

Question 59

2nd class (largest) of extracellular signaling molecules:

Answer 59

-extracellular signaling molecules are sufficiently small and hydrophobic to diffuse across the plasma membrane -receptors are in the interior of the target cell, either in the cytosol or in the nucleus

Question 60

Signaling through extracellular signaling molecules: A receptor protein located on the cell surface receives the extracellular signaling molecule and:

Answer 60

generates a new intracellular signaling molecule in response (protein or second messenger).

Question 61

Signaling through extracellular signaling molecules: There are 3 classes of ligand-triggered cell-surface receptors:

Answer 61

1. G-protein-coupled receptors – found in virtually all cells 2. Ion-channel-coupled receptors – especially important in neuronal signaling 3. Enzyme-coupled receptors

Question 62

class of ligand-triggered cell-surface receptors found in virtually all cells

Answer 62

G-protein -coupled receptors

Question 63

class of ligand-triggered cell-surface receptors – especially important in neuronal signaling :

Answer 63

Ion-channel-coupled receptors

Question 64

Some G proteins stimulate the production of 1,2 diacylglycerol and inositol-1,4,5-triphosphate by activating phospholipase C and are referred to as

Answer 64

Gq

Question 65

Some G proteins stimulate the production of cAMP and are referred to a

Answer 65

Gs

Question 66

Some G proteins stimulate the production of cAMP and are referred to as Gs. Others inhibit the production of cAMP and are called

Answer 66

Gi

Question 67

The subunits of the heteromeric G protein are called

Answer 67

Gqa for the a subunit and Gqby for the by subunits.

Question 68

ligand-triggered cell-surface receptors:ion-channel-coupled receptors Ligand binding changes

Answer 68

the conformation of the ion-channel-linked receptor and opens the channel for ion flow

Question 69

ligand-triggered cell-surface receptors:An enzyme-coupled receptor ___ switching on an __ of the plasma membrane.

Answer 69

An enzyme-coupled receptor BINDS ITS EXTRACELLULAR LIGAND switching on an ENZYME ACTIVITY ON THE OPPOSITE SIDE of the plasma membrane.

Question 70

An enzyme-coupled receptor binds its extracellular ligand switching on an enzyme activity on the opposite side of the plasma membrane. The enzyme may be part of (2):

Answer 70

(1) cytoplasmic domain of the receptor (2)an enzyme that associates with the cytoplasmic domain of the receptor

Question 71

2nd class of extracellular signaling molecules and receptors: Some extracellular signaling molecules are sufficiently small and hydrophobic to diffuse across the plasma membrane. The corresponding receptors are in (2):

Answer 71

the interior of the target cell, either in the cytosol or in the nucleus.

Question 72

2nd class of extracellular signaling molecules and receptors:Two groups of small, diffusible signaling molecules:

Answer 72

1. Hormones 2. Nitric oxide (NO)

Question 73

group of small, diffusible signaling molecules: 1. Hormones – their receptors are __

Answer 73

transcription factors that regulate expression of specific genes.

Question 74

group of small, diffusible signaling molecules: 2. Nitric oxide (NO) – Produced by __

Answer 74

the breakdown of arginine

Question 75

group of small, diffusible signaling molecules: 2. Nitric oxide (NO) – only involved in what kind of signalling

Answer 75

short-lived so only local acting (paracrine signaling),

Question 76

what group of small diffusable signaling molecules is important in the cardiovascular system:

Answer 76

Nitric oxide (NO)

Question 77

Cortisol(hormone-example of small diffusable signalling molecule) binds to its receptor in the

Answer 77

cytosol

Question 78

thyroxine(hormone-example of small diffusable signalling molecule) binds to its receptor in the:

Answer 78

nucleus

Question 79

Cortisol is produced by

Answer 79

adrenal gland

Question 80

Cortisol is produced by the adrenal gland under (2):

Answer 80

(1) stress (2) low blood glucose

Question 81

cortisol causes the body to (2):

Answer 81

(1) Produce glucose (2) Suppress the immune system

Question 82

Describe the 3 steps involved in cortisol binding to its receptor

Answer 82

(1) Cortisol diffuses across the plasma membrane and binds to its receptor protein, which is located in the cytosol. (2) The binding of cortisol induces a conformational change in the receptor and the complex of cortisol and its receptor are transported into the nucleus through nuclear pores. (3)In the nucleus, the receptor binds to specific DNA regulatory sequences and induces expression of the downstream genes.

Question 83

Thyroxine receptor is located in the

Answer 83

nucleus

Question 84

Thyroxine receptor is located in the nucleus and is bound to DNA either (2):

Answer 84

in the presence or absence of thyroxine.

Question 85

Thyroxine receptor is located in the nucleus and is bound to DNA either in the presence or absence of thyroxine. In the ABSENCE of thyroxine, the receptor

Answer 85

binds to a REPRESSOR molecule to prevent gene transcription.

Question 86

Thyroxine is produced by

Answer 86

the thyroid gland

Question 87

Thyroxine is produced by the thyroid gland and increases:

Answer 87

(1) metabolic rate (2) protein synthesis

Question 88

can thyroxine diffuse across the plasma membrane ? if so , how

Answer 88

can diffuse across the plasma membrane where it is transported from the cytosol into the nucleus through NUCLEAR PORES

Question 89

In the nucleus, binding of thyroxine to its receptor induces

Answer 89

a conformational change such that the receptor now binds to a transcriptional activator, which in turn recruits RNA polymerase. The gene is then transcribed.

Question 90

a vasodilator, causing the smooth muscle cells lining blood vessels to relax, allowing blood to flow more readily

Answer 90

NO

Question 91

NO is a vasodilator, causing the smooth muscle cells lining blood vessels to relax, allowing blood to flow more readily. Produced through the action of

Answer 91

acetylcholine.

Question 92

NO activates ___ , an enzyme that produces __

Answer 92

NO activates guanylyl cyclase, an enzyme that produces cGMP

Question 93

NO is a vasodilator, causing the smooth muscle cells lining blood vessels to relax, allowing blood to flow more readily. Produced through the action of acetylcholine. It activates guanylyl cyclase, an enzyme that produces cGMP, cGMP is a second messenger that activates

Answer 93

a protein kinase that phosphorylates specific substrates leading to smooth muscle cell relaxation and vasodilation

Question 94

therapeutic persepective NO:

Answer 94

Nitroglycerin, used to treat angina (inadequate blood flow to the heart), is converted to NO leading to vasodilation.

Question 95

Increasing the lifetime of cGMP will increase

Answer 95

blood flow for greater periods of time.

Question 96

Increasing the lifetime of cGMP will increase blood flow for greater periods of time. Inhibitors of __ (sildenafil, a.k.a. Viagra) achieve this

Answer 96

phosphodiesterase 5