Receptors I

Question 1

What drug type creates a response in the cell

Answer 1

agonist

Question 2

What is occupation of a drug-receptor governed by?

Answer 2

Affinity

Question 3

What is activation of a drug-receptor governed by?

Answer 3

efficacy

Question 4

What part of a drug receptor reaction is reversible

Answer 4

occupation forming a complex

Question 5

What is the ratio of reversibility of a drug receptor reaction governed by?

Answer 5

affinity of the drug

Question 6

Describe the reversibility of drugs with high affinities

Answer 6

slow reversibility

Question 7

Describe occupancy

Answer 7

proportion of receptors occupied will vary with the drug concentration

Question 8

What does occupancy vary between

Answer 8

0 and 1

Question 9

How much drug is present at 0 occupancy

Answer 9

none

Question 10

How can we measure occupancy

Answer 10

by measuring response

Question 11

Describe the relationship between occupancy and response

Answer 11

high occupancy means there is a large response

Question 12

Can you measure antagonists activity using occupancy

Answer 12

NO

Question 13

Examples of ligands

Answer 13

neurotransmitters, hormones, growth factors, cytokines, drugs, toxins

Question 14

Examples of protein targets

Answer 14

receptors, ion channels, enzymes, transporters

Question 15

Describe a ligand binding practical

Answer 15

tissue prep with radio-ligand, incubation, filtration, rinse, count, data analysis

Question 16

True or False - most ligands bind non-specifically to tissue, filter paper, glass

Answer 16

TRUE

Question 17

How can non-specific ligand binding be reduced

Answer 17

reduced by anti-absorbants

Question 18

What are some examples of anti-absorbants

Answer 18

albumin, collagen, o-catechol

Question 19

What is the function of rinsing in a ligand binding practical

Answer 19

remove unbound radioligand from incubation medium

Question 20

What is a key measurement in receptor ligand assays

Answer 20

specific and non specific binding

Question 21

What are the disadvantages of using a radio ligand

Answer 21

degradation

Question 22

How can you prevent degradation of radio ligands

Answer 22

free radical scavenger, store at low temp, avoid light, incorporation of antioxidant

Question 23

What are radio ligands labelled with

Answer 23

radio active labels

Question 24

Name two radio labels

Answer 24

tritum, iodine

Question 25

What are the disadvantages of tritum

Answer 25

specialised labs required, expensive

Question 26

What are the advantages of tritum as a label

Answer 26

high specific activities, good stability, long half life

Question 27

What are the advantages of iodine as a label

Answer 27

easy and cheap, if aromatic hydroxyl group can be incorporated at high specific activities

Question 28

What are the disadvantages of iodine

Answer 28

more readily degraded, short half life, activity of ligand can be reduced

Question 29

What tissue would you select for your ligand binding practical

Answer 29

tissue that contains the receptors of interest

Question 30

What can the tissue be in the ligand binding practical

Answer 30

isolated membranes, slices, synaptosomes, purified receptors

Question 31

What must incubation preserve

Answer 31

integrity of ligands and binding sites

Question 32

What happens during the tissue incubation period of the ligand binding practical

Answer 32

enzymes are liberated

Question 33

What is the effect of enzymes being liberated during the tissue incubation period

Answer 33

enzymes break down receptors of interest

Question 34

What are the enzymes liberated during the tissue incubation period

Answer 34

proteases

Question 35

How can the effect of enzymes be minimised during the tissue incubation period

Answer 35

protease inhibitors added for peptides, anti-oxidants if ligand is oxidisable

Question 36

What is the temperature during the incubation period

Answer 36

low room temperature to 0 degrees

Question 37

How is the tissue and bound ligand separated from free ligand

Answer 37

filtration or centrifugation

Question 38

What is a problem when separating bound ligand from free ligand during the practical

Answer 38

rate of dissociation of ligand-receptor complex

Question 39

What must speed of separation of bound ligand from free ligand be compatible with

Answer 39

affinity of ligand for receptor

Question 40

What type of separation does lower affinity of ligand receptor require

Answer 40

faster/more efficient separation

Question 41

How do you work out specific binding

Answer 41

subtract non specific binding from total bound

Question 42

How is ligand receptor binding data plotted

Answer 42

semi-logarithmic scale

Question 43

What is saturable binding

Answer 43

specific binding

Question 44

Why is radio-ligand binding saturable

Answer 44

total number of receptors is limited

Question 45

What does the Langmuir equation describe

Answer 45

relationship between receptor occupancy, affinity and drug concentration

Question 46

What is Bmax in the Scatchard equation

Answer 46

maximum amount of drug which can bind specifically to receptors

Question 47

What is F in the Scatchard equation

Answer 47

free ligand concentration

Question 48

What is KD in the scatchard equation

Answer 48

dissociation constant for radio ligand

Question 49

What determines the dissociation constant for the radio ligand

Answer 49

saturation analysis

Question 50

What is KD a measure of

Answer 50

affinity

Question 51

What does high KD show

Answer 51

low affinity