Chapter 5 Cell Signalling in Physiology

Question 1

The first step in the action of any intercellular chemical messenger is the binding of the messenger to specific target-cell proteins known as _________

Answer 1

The first step in the action of any intercellular chemical messenger is the binding of the messenger to specific target-cell proteins known as receptors (or receptor proteins)

Question 2

A chemical messenger is a _____ and the receptor has a _____ _____ for that specific messenger

Answer 2

A chemical messenger is a ligand and the receptor has a binding site for that specific messenger

Question 3

The binding of a messenger to the receptor changes the ______ (_____ structure) of the receptor

Answer 3

The binding of a messenger to the receptor changes the conformation (tertiary structure) of the receptor

Question 4

Changing the conformation of a receptor effectively _____ the receptor

Answer 4

Changing the conformation of a receptor effectively activates the receptor

Question 5

What is signal transduction?

Answer 5

Signal transduction is the process by which the binding of a messenger to a receptor activates a sequence of events that lead to a cell response

signal= receptor activation

transduction= the process by which a stimulus is transformed into a response

Question 6

Receptors that bind intercellular chemical messengers are ______ or _____ located either in the ______ or inside the cell in the _____ or the ______

Answer 6

Receptors that bind intercellular chemical messengers are proteins or glycoproteins located either in the plasma membrane or inside the cell in the nucleus or the cytosol

Question 7

Why is the plasma membrane the most common location for receptors?

Answer 7

A large number of messengers are water-soluble (not lipid-soluble) and therefore cannot diffuse across the plasma membrane

Question 8

Plasma membrane receptors are _____, that is, they span the entire membrane thickness

Answer 8

Plasma membrane receptors are transmembrane proteins, that is, they span the entire membrane thickness

Question 9

Arriving chemical messengers bind to the extracellular parts of the receptor; the intracellular regions of the receptors are involved in ______ _____ events

Answer 9

Arriving chemical messengers bind to the extracellular parts of the receptor; the intracellular regions of the receptors are involved in signal transduction events

Question 10

Intracellular receptors exist in either the _____ or the _____

Answer 10

Intracellular receptors exist in either the cytosol or the nucleus

Question 11

Like plasma membrane receptors, intracellular receptors have a segment that binds the ______ and segments that act as _______ ______. Unlike plasma membrane receptors, intracellular receptors also have a segment that binds to______

Answer 11

Like plasma membrane receptors, intracellular receptors have a segment that binds the messenger and segments that act as regulatory sites. Unlike plasma membrane receptors, intracellular receptors also have a segment that binds to DNA

Question 12

What is a key distinction between Plasma Membrane Receptors and Intracellular receptors?

Answer 12

Plasma membrane receptors can transduce signals without interacting with DNA whereas all intracellular receptors transduce signals through interactions with genes

Question 13

What are the four major features that define the interactions between receptors and their ligands?

Answer 13

1. specificity
2. affinity
3. saturation
4. competition

Question 14

What is Receptor specificity?

Answer 14

The ability of a receptor to bind to only one type (or a limited number of structurally related types) of chemical messengers.

• means that only cells that express the particular receptor will be affected by a particular messenger

Question 15

What is saturation (concerning receptors)?

Answer 15

The degree to which receptors are occupied by messengers.

If all are occupied the receptors are fully saturated; if only half are occupied the receptors are at 50% saturation and so on

Question 16

What is affinity (in regards to receptors)

Answer 16

The strength with which a chemical messenger binds to its receptor

higher affinity = higher chance of bonding

Question 17

What is receptor competition?

Answer 17

The ability of different molecules to compete with a ligand for binding to its receptor

Competitors are usually similar in structure to the natural ligand

Question 18

What is a receptor antagonist?

Answer 18

A molecule that competes with a ligand for binding but does not activate signalling normally associated with the natural ligand

i.e. Antagonists prevent the actions of the natural ligand

eg certain antihistamines

Question 19

What is a receptor agonist?

Answer 19

Chemical messenger that binds to a receptor and triggers the cell’s response - often refers to a drug that mimics a normal messenger’s action

eg some decongestants are agonists

Question 20

What is down regulation (terms of receptors)? When might it occur?

Answer 20

A decrease in the total number of target-cell receptors for a given messenger; may occur in response to chronic high extracellular concentration of the messenger

Question 21

What is up-regulation (in terms of receptors) and when might it occur?

Answer 21

An increase in the total number of target-cell receptors available for a given messenger; may occur in response to a chronic low extracellular concentration of the messenger

Question 22

What is increased sensitivity (in regards to receptors)?

Answer 22

The increased responsiveness of a target cell to a given messenger; may result from up-regulation of receptors

Question 23

The general term for a compound that blocks the action of a chemical messenger is:

Answer 23

Antagonist

Question 24

The true chemical messenger is termed the ______ messenger

Answer 24

The true chemical messenger is termed the endogenous messenger

Question 25

Down regulation represents what kind of feedback mechanism?

Answer 25

Negative Feedback:

intense prolonged stimulation results in fewer receptors = reduce cell’s responsiveness to frequent or intense stimulation (i.e desensitize the cell)

Question 26

How is down regulation possible?

Answer 26

there is continuous synthesis and degradation of receptors

Question 27

The main mechanism of down-regulation of plasma membrane receptors is:

Answer 27

Internalization

Question 28

What happens during internalization?

Answer 28

1. messenger binds to receptor
2. stimulates messenger-receptor complex to be taken into the cell via receptor-mediated endocytosis
3. increases rate of degradation within the cell
4. higher concentration of messenger = more internalization = gradual decrease in receptors

Question 29

up regulation is the _________ of a cell receptor to a messenger as a result of prolonged exposure to low messenger concentrations

Answer 29

up-regulation is the increased sensitivity of a cell receptor to a messenger as a result of prolonged exposure to low messenger concentrations

Question 30

How is up-regulation and down-regulation an example of the principle of homeostasis?

Answer 30

Acts to return signal strength to normal when the concentration of messengers varies above or below normal

Question 31

What is receptor activation?

Answer 31

the conformation change that occurs when a messenger binds to a receptor

Question 32

What are five possible types of cell responses to a messenger?

Answer 32

Changes in the

1. permeability, transport properties, or electrical state of the plasma membrane
2. metabolism
3. secretory activity
4. rate of proliferation and differentiation
5. contractile or other activities

Question 33

The diverse sequences of events that link receptor-activation to cellular responses are termed:

Answer 33

Signal transduction pathways

Question 34

Lipid soluble messengers include:

Answer 34

hydrophobic substances such as steroid hormones or thyroid hormones

Question 35

Lipid soluble messengers bind to _____ receptors (intracellular receptors)

Answer 35

Lipid soluble messengers bind to nuclear receptors (intracellular receptors)

Question 36

in a few cases, inactive intracellular receptors are in the ______ and move into the _____ after binding to their ligand

Answer 36

in some cases, inactive intracellular receptors are in the cytosol and move into the nucleus after binding to their ligand

Question 37

Most of the inactive intracellular receptors are located in the _____ where they bind to and are activated by their respective ligands

Answer 37

Most of the inactive intracellular receptors are located in the nucleus where they bind to and are activated by their respective ligands

Question 38

Intracellular receptor activation leads to altered rates of _____ of one or more genes in a particular cell

Answer 38

Intracellular receptor activation leads to altered rates of transcription of one or more genes in a particular cell

Question 39

Is it possible for more than one gene to be subject to control by a single receptor site?

Example?

Answer 39

Yes

Adrenal gland hormone cortisol activates numerous genes involved in the coordinated control of cellular metabolism and energy balance

Question 40

in some cases, the transcription of a gene (or genes) may be _____ by the activated receptor

Example?

Answer 40

in some cases, the transcription of a gene (or genes) may be decreased by the activated receptor

Cortisol inhibits transcription of several genes whose protein products mediate inflammatory responses (anti-inflammatory)

Question 41

Water soluble messengers include most ______ hormones, ______ and _____ and _____ compounds

Answer 41

Water soluble messengers include most polypeptide hormones, neurotransmitters, and paracrine and autocrine compounds

Question 42

What are first messengers?

Answer 42

extracellular chemical messengers that reach the cell and bind to their specific plasma membrane receptors

Question 43

What are second messengers?

Answer 43

substances that enter (or are generated in) the cytoplasm as a result of receptor activation by the first messenger

-chemical relays from plasma membrane to biochemical machinery within the cell

Question 44

What is protein kinase?

Answer 44

enzyme that phosphorylates other proteins by transferring a phosphate group to them from ATP

-alters protein’s activity by allosterically changing tertiary structure of a protein