Introduction Flashcards
(153 cards)
1
Q
Define pharmacology.
A
Study of Mechanisms by which drugs affect function of living systems.
2
Q
What is a drug?
A
Biologically active compound.
3
Q
What is a receptor?
A
Protein which signals a response upon activation by a ligand.
4
Q
What is an agonist?
A
Drug that binds to a receptor to produce a response.
5
Q
What is an antagonist?
A
Drug that prevents a response of an agonist.
6
Q
What is occupancy?
A
Proportion of receptors occupied by agonist.
7
Q
What is the formula for occupancy?
A
Number of receptors occupied / Total number of receptors
8
Q
How can occupancy be measured directly?
A
Prepare pig ileum by treating with detergent and centrifuge
Aliquot membranes onto filters
Apply radiolabeled agonist at different concentrations and equilibrate
Remove unbound agonist via filtration
Measure radioactivity of filter
9
Q
When measuring occupancy directly, why is the total binding count different from the specific binding count and which is the accurate representation of occupancy?
A
Total binding count includes specific and non-specific binding counts. Non-specific binding count represents the amount of drug being bound to non-biological material such as the filter itself. Specific binding count corresponds to the amount of agonist bound to the receptors hence gives an accurate measure of occupancy.
10
Q
Give the formula for the law of mass action.
A
rate = (k+1)[agonist][free receptor]
rate = (k-1)[agonist-receptor complex]
At equilibrium:
(k+1)[agonist][free receptor] = (k-1)[agonist-receptor complex]
11
Q
Give the formula for calculating KD.
A
KD = ((Xa)(Ntot-Na)/(Na)
12
Q
Give the formula for KD in terms of rate constants.
A
KD = k-1/k+1
13
Q
Give the formula for calculating occupancy Pa.
A
Pa = Xa/(KD+Xa)
14
Q
Give the formula for occupancy in terms of the receptor agonist ratio.
A
Pa = Na/Ntot
15
Q
Give the Langmuir equation.
A
Moles bound = Maximum moles of drug bound per mg of protein x occupancy
Bound = (Bmax)(Pa)
16
Q
What is the Langmuir equation used for?
A
Conversion of occupancy to actual data.
17
Q
Define affinity.
A
Probability of the drug binding to the receptor at any time.
18
Q
How is KD used to estimate affinity?
A
A low KD (KD<1) means that rate of the backward reaction is lower than the rate of the forward reaction. This suggests that agonist is more likely to associate with a receptor than dissociate from it meaning it has a high affinity for the receptor. Vice versa.
19
Q
Why can’t the biological response be determined from the affinity of the agonist for the receptor?
A
Biological response is the consequence of the binding of agonist and receptor and not the binding itself. Responses may be amplified after the agonist is bound. Different responses need different proportions of bound receptors.
20
Q
How are biological responses compared?
A
By their EC50 - concentration of agonist needed to produce 50% of the max response.
21
Q
Can EC50 be used to compare different drugs?
A
No, some drugs may not evoke a full response - partial agonists.
22
Q
What is receptor reserve?
A
Spare receptors that don’t need to be bound to evoke a full response.
23
Q
What is the function of the receptor reserve?
A
To enable chemicals to evoke a maximal response even when some receptors are occupied by an antagonist or other.
24
Q
Give the formula for calculatin response.
A
Response = (Maximum Response x Concentration of Agonist^Hill Slope Factor)/((Concentration of Agonist^Hill Slope Factor) + (EC50^Hill Slope Factor)) Response = (max)(Xa^n)/((Xa^n) + (EC50^n))
25
What is potency?
Amound of drug needed to produce a response.
26
What is the Hill Slope Factor?
Measure of steepness of the response curve.
27
What can be determined from the HSF?
Whether one or mole molecule is needed to produce a response.
HSF>1 - More than 1 molecule is needed
HSF<1 - More than 1 receptor subtype exists
28
What is efficacy?
Measure of a single agonist-receptor's ability to generate a response
29
What are the classes of antagonism?
Chemical
Pharmacokinetic
Physiological
30
Outline the basis of chemical antagonism with an example.
Antagonist binds to the agonist in solution
| e.g.: Inactivation of heavy metals with dimercaprol - a chelating agent.
31
Outline the basis of pharmacokinetic antagonism with an example.
Inhibition of absorption of agonist in the GI tract (opiates).
Changing the rate of excretion of agonist (aspirin)
Changing the metabolism of agonist (Antibiotics on warfarin)
32
Outline the basis of physiological antagonism with an example.
Interaction of two drugs which have an opposite effect on the body. Noradrenaline increases heart rate, histamine does the opposite.
33
What is a non-competitive antagonist?
Antagonist which doesn't compete for the receptor site. Blocks the pathway between binding and response.
34
What is a competitive antagonist?
Antagonist which acts at the level of the receptor. Competes for occupancy.
35
What is a reversible competitive antagonist?
Antagonist which can be washed off of the receptor to stop its action.
36
What is an irreversible competitive antagonist?
Antagonist which dissociates slowly or not at all. Some form a chemical (alkyl) bond with the receptor.
37
What is the Dose Ratio?
The ratio of agonist in the presence of an antagonist needed to evoke the same response.
38
How is DR calculated?
DR = [agonist in presence of antagonist]/[agonist in absence of antagonist]
39
What is pA2?
Measure of potency of antagonists.
40
How is pA2 calculated?
-log10[antagonist] that gives a dose ratio of 2.
41
What is the relationship between pA2 and strength of antagonist?
The greater the pA2 the stronger the antagonist. if pA2 = 6 then 1x10^-6M of antagonist are needed to give a dose ratio of 2.
42
How is DR calculated in terms of antagonist concentrations?
DR = [antagonist]/(antagonist equilibrium constant + 1)
43
What are the axes labels of a Schild plot?
y - log(DR-1)
| x - log[Antagonist]
44
How can pA2 be estimated from a Schild plot?
pA2 is the negative of the x intercept of a Schild plot.
45
How is irreversible competitive antagonism time-dependent?
The longer the antagonist is bound the stronger its effect.
46
Why does irreversible competitive antagonism affect the max response after a while?
At first it uses up the receptor reserve.
47
Give an example of irreversible competitive antagonism.
Dibenamine is an antagonist to histamine receptors.
48
What is does study of pharmacokinetics involve?
Study of the time-course of drug action and how the drugs are processed in the body.
49
What are the stages of pharmacokinetics?
Absorption
Distribution
Metabolism
Excretion
50
What defines pharmacokinetic absorption?
Movement of drug from site of administration to plasma.
51
Give examples of routes of drug administration.
Sublingual (under the tongue)
| Epithelial (cornea)
52
What factors determine the site of drug administration?
Molecular weight
Lipid solubility
pH/ionisation
Transport (passive/active)
53
What are the major body compartments for drug distribution?
Extracellular fluid (plasma/interstitial/lymph)
Intracellular fluid
Transcellular fluid (cerebrospinal fluid)
Fat
54
What is the blood-brain barrier?
Wall of endothelial cells in the brain.
| Connected by tight junctions which prevents drugs from entering CSF.
55
What can affect the blood-brain barrier?
Inflammation.
56
What is meant by drug metabolism?
Inactivation of drugs prior to excretion.
57
What are the two phases of drug metabolism
Phase 1 - Red/Ox/Hydrolysis
| Phase 2 - Conjugation of functional groups
58
In what ways can drugs be excreted?
Renal - Penicillin cleared after single kidney filtration
GI - Billiary excretion through liver
Lungs
59
Describe the one compartment model of pharmacokinetics.
KA - Rate of absorption
VD - Volume of distribution
CP - Concentration in plasma
Kel - Rate of elimination
Kel is proportional to CP.
Decrease in CP is exponential.
Plasma half-life proportional to VD and inversely proportional to Kel
60
How can a steady concentration of drug in plasma be established?
Repeated doseage.
61
When is the two compartment model applied?
When drug disappearance doesn't follow the trends of the one compartment model. A second compartment must exist where the drug may enter/leave via the central compartment.
62
What is a ligand?
A molecule which binds specifically to a receptor.
63
Why don't antagonists have efficacy?
Don't activate receptors.
64
Give an example of an agonist.
Salbutamol - Beta-2 adrenergic receptor agonist.
65
Give an example of an antagonist.
Tamoxifen - Oestrogen receptor antagonist
| Beta blockers - Beta-adrenergic receptor antagonists.
66
What are the 3 classes of drug targets?
Proteinous
Nucleic acids
Idiosyncratic
67
What molecules belong to the idiosyncratic class of drug targets?
Anti-acids
68
What molecules belong to the nucleic acid class of drug targets?
DNA
| mRNA/siRNA/shRNA
69
What are the types of proteinous drug targets?
Transporters
Ion Channels
Receptors
Enzymes
70
What are the 2 types of drugs that affect transporters and what are their individual functions? Give an example.
False substrates - Compete with normal substrates for the carrier. Cause accumulation of abnormal product.
e.g.: Amphetamine false substrate for noradrenaline uptake 1 transporter. Causes accumulation of NA in synaptic cleft. Leads to prolonged neuronal stimulation
Inhibitors - Block transport.
e.g.: Cocaine. Inhibits Noradrenaline uptake 1 transporter.
71
What are the 2 types of drugs that affect ion channels and what are their individual functions? Give an example.
Modulators - Bind to channels and affect gating.
e.g.: Sulfonylurea. Acts on K+ ATPase channels
Blockers - Physically block the channel.
e.g.: Tetrodotoxin. Blocks Na+ VGCs.
72
What are the 2 types of receptors?
Nuclear
| Cell surface
73
What type of ligand would bind to a nuclear receptor? Give examples.
```
Hydrophobic ligands:
Steroid hormones
Thyroid hormones
Fatty acids
Vitamin D
Retinoic acid
```
74
What is the function of nuclear receptors?
Regulation of transcription via binding to DNA.
75
Give 2 examples of drugs that act on nuclear receptors.
Tamoxifen - treatment of oestrogen dependent breast cancer.
| Thiazolidinediones - PPAR-gamma receptor agonist. Treatment of type 2 diabetes.
76
What type of ligand would bind to a cell surface receptor?
Hydrophilic ligands:
Neurotransmitters
Protein hormones
Growth factors
77
Outline the structure of a cell surface receptor.
Extracellular domain - ligand binding site.
Transmembrane-spanning domain - Alpha-helical structure.
Intracellular domain.
78
What is the function of cell surface receptors?
Transduction of signals onto target proteins.
79
Give examples of target protein types.
Metabolic enzymes
Gene/regulatory protein
Cytoskeletal protein
80
What are the 3 classes of cell surface receptors?
Ligand-gated ion channels (ionotropic)
G-protein coupled receptors (metabotropic)
Enzyme linked receptors
81
What are the 3 types of drugs that affect enzymes and what are their individual functions? Give an example.
False substrates - Form abnormal product which inhibits the metabolic pathway.
e.g.: Methyldopa. Binds to Dopadecarboxylase to form methylnorepinephrine.
Inhibitors - Bind to enzyme and block it's activity.
e.g.: Aspirin. Inhibits cyclooxygenase.
Pro-drugs - Inactive molecules which use the enzyme to convert to the active form.
e.g.: Enalapril. Converted to enalaprilat. Inhibits angiotensynogen converting enzyme (ACE)
82
What is the difference between Competitive and non-competitive enzyme inhibitors?
Competitive inhibitors block the active site whereas the non-competitive inhibitors bind to an allosteric site on the ezyme
83
Give an example of a reversible competitive enzyme inhibitor.
Ibuprofen. Acts on cyclooxygenase
84
Give an example of an irreversible competitive enzyme inhibitor.
Aspirin. Acts on cyclooxygenase
85
What are the 2 ligand groups that act on ligand gated ion channels?
Neurotransmitters
| Nucleotides
86
Give 3 neurotransmitters that act on ligand gated ion channels.
Glutamate
Acetylcholine
Gamma-aminobutyric acid
87
What type of receptor does glutamate act on? Give examples.
Ionotropic glutamate receptors.
NMDA
AMPA
Kalnate
88
What effect does glutamate have on receptors?
Causes a nerve impulse.
89
What type of receptor does acetylcholine act on?
Nicotinic acetylcholine receptors (nAChR).
90
Describe the structure of a nAChR.
Pentameric: 2x alpha, beta, gamma, delta.
91
Where on a nAChR is the ACh binding site?
Extracellular domain of alpha subunits.
92
What effect does ACh have on nAChR?
Causes a nerve impulse that leads to a muscular contraction.
93
Name a nAChR agonist other than ACh.
Nicotine.
94
Name a nAChR antagonist.
Alpha-conotoxin.
95
What type of receptor does GABA act on?
GABA receptors.
96
What is the function of GABA receptors?
Transport of anions.
97
What effect does GABA have on the GABA receptor?
Causes hyperpolarisation of the axon. Inhibits neuronal activity
98
What is the general purpose of neurotransmitter-gated receptors?
Regulation of electrical signalling in the nervous system.
99
What is the largest family of cell-surface receptors?
Metabotropic receptors (GPCRs)
100
Give examples of GPCR agonists.
```
Some neurotransmitters (mAChR)
Hormones
Photons
Metabolites
Odourants
```
101
Describe the structure of a G-protein
Heterotrimer. 3 subunits: Alpha, Beta, Gamma.
102
What is the function of the Alpha subunit?
Together with gamma, couples the receptor with an effector.
| Binds to GTP and hydrolyses it to GDP.
103
What is meant by intrinsic GTPase activity?
Ability to metabolise GTP natively.
104
How do G-proteins vary?
Differ in combinations of subunits.
16+ Alpha variants
6+ Beta variants
9 Gamma variants
105
Give 3 examples of G-protein alpha subunit variants.
Gs
Gi
Gq
106
What is the unique function of the GsPCR?
Stimulation of adenylyl cyclase to produce cAMP.
107
How can a GsPCR be inhibited?
By application of cholera toxin.
108
What is the unique function of the GiPCR?
Inhibition of adenylyl cyclase. Reduces cAMP production.
109
How can a GiPCR be inhibited?
By application of pertussis toxin.
110
What is cAMP?
Cyclic adenosine monophosphate. A secondary messenger
111
What is the function of cAMP?
Relay of signal onto PKA.
112
What is PKA?
Protein Kinase A. A target protein.
113
What is the function of PKA?
Regulation of physiological functions e.g.: increasing heart rate.
114
What is the effect of activation of GsPCR or GiPCR on heart rate?
GsPCR causes increase in heart rate.
| GiPCR causes decrease in heart rate.
115
What is the unique function of the GqPCR?
Stimulation of Phospholipase C-Beta. Increased production of IP3 and DAG from PIP2
116
What is the function of IP3?
Acts on an IP3 receptor on ER to release Calcium ions causing contraction.
117
What is the function of DAG?
Activation of PKC which causes contraction.
118
What are IP3 and DAG?
Inositrol thisphosphate; Diacylglycerol. Secondary messengers.
119
What is PKC?
Protein Kinase C. A target protein.
120
Describe the structure of a GPCR.
Singlt polypeptide chain. 7 transmembranal domains (radiator).
121
Where in a GPCR does ligand binding occur?
Extracellular domain.
| 2nd/3rd transmembranal domain.
122
Which parts of the GPCR are highly variable?
COOH tail.
| 3rd intracellular loop.
123
What changes occur in the GPCR upon activation?
Binding of ligand causes a conformational change in the receptor.
Activated receptor binds to the G-protein, which is associated with GDP (inactive), and acts as a Guanine nucleotide Exchange Factor (GEF).
Binding causes GDP to be replaced with GTP (GEF action).
GTP-bound alpha subunit dissociates from the ligand-bound receptor and beta/gamma complex.
Ligand dissociates from receptor and alpha subunit binds to/activates effector.
GTP is hydrolysed to GDP via intrinsic GTPase activity of the alpha subunit. This causes the alpha subunit to dissociate from effector and reassociate with beta/gamma subunits.
124
Describe the G-protein cycle.
```
G-protein GDP-bound (at rest).
GTP replaces GDP.
Beta/gamma subunits dissociates.
Alpha subunit GTP-bound (active).
H2O binds to alpha subunit
Beta/gamma subunits reassociate.
Pi is given off.
G-protein is at rest again.
```
125
How do GPCRs regulate ion channels?
The G-protein acts on the channel directly instead of causing production of secondary messengers.
126
Why is GPCR regulated ion channel activation slower than ligand-gated channel activation?
The former uses a GPCR to act on the channel whereas the latter acts on the channel directly.
127
Give an example of a GPCR-regulated ion channel.
Muscarinic M2 ACh Receptor.
128
How are signals amplified in their secondary messenger pathways.
Signal relayed onto multiple receivers.
| Exponential increase of sub-signals with each step.
129
Name a class of enzyme-linked receptors.
Tyrosine Kinase receptors.
130
What is the active catalytic domain of RTKs?
Intrinsic tyrosine kinase activated by a ligand.
131
What types of ligands activate RTKs? Give examples.
Peptide Growth factors - EGF.
| Hormones - Insulin.
132
What are RTKs used for?
Metabolism
Differentiation
Cell-cycle
133
Describe the structure of an RTK.
Extracellular ligand-binding domain.
Transmembrane domain
Intracellular TK domain
134
What are the steps of TK activation?
Ligand binding
Dimerisation
Tyrosine phosphorylation (Autotransphosphorylation)
135
Which RTK receptor skips the dimerisation step?
Insulin receptor.
136
Name 2 signalling molecules that may be recruited by RTKs
PTB - Phosphotyrosine binding domain
| SH2 - Scr Homology 2 domain
137
Where on the RTK do signalling molecules bind to?
Phosphorylated tyrosine
138
How do signalling molecules cause activation of linked enzymes?
Signalling molecules induce a conformational change in the enzyme.
Enzyme is phosphorylated.
Enzyme brought nearer its substrate.
139
Give 3 examples of enzymes linked to receptors.
PLC-gamma - Phospholipase C-gamma
Src - Tyrosine kinase
Shp2 - Phosphatase
140
What are adaptor proteins?
Proteins which bind to phosphorylated RTKs.
141
How do adaptor proteins work?
Act as adaptors to connect other proteins to the receptor. Contain SH2 and SH3 domains. SH2 binds to receptor. SH3 free for binding other molecules.
142
Give an example of an adaptor protein.
Grb2 - Growth factor receptor binding protein.
143
What are docking proteins?
Proteins which bind to the RTK and acy as extension leads/splitters for binding sites (phosphorylated tyrosines)
144
How do docking proteins work?
Contain a PTB domain which binds to the RTK. Contain a PH domain and a chain of tyrosines which allows binding of multiple other proteins that have compatible domains (PTB/SH2).
Can be used to form series of docking chains.
145
Give an example of a docking protein.
IRS - Insulin receptor substrate.
146
Describe the pathway of direct recruitment/activation of PLC-gamma and its effect.
The platelet derived growth factor (PDGF) receptor phosphorylates PLC-gamma
PLC-gamma cleaves PIP2 into DAG and IP3.
DAG activates PKC.
IP3 acts on IP3 receptors on ER to release calcium.
PKC and calcium influx causes muscle contraction.
147
Describe the MAPK pathway activation.
```
EGF receptor binds to an adaptor protein GRB.
Adaptor has a SH2 and SH3 domain.
SH2 binds to the receptors.
SH3 allows binding of the SOS enzyme.
SOS is a GEF. Acts on the small G-protein Ras.
Binding of GTP to Ras turns it on.
Ras phosphorylates the Raf protein.
Raf phosphorylates the MEK protein.
MEK phosphorylates the MAPK protein.
```
148
What is the MAPK protein involved in?
Cell growth/proliferation.
149
Describe the Insulin signalling pathway via the IRS1 docking protein.
IRS1 - Insulin receptor substrate 1. Contains a PTB domain which binds to phosphorylated tyrosines.
Receptor phosphorylates IRS.
IRS may recruit GRB to trigger the MAPK pathway.
IRS may recruit PI3 kinase.
PI3 - Phosphatidylinositol 3'-kinase.
PI3 binds to IRS1 via it's SH2 domain.
PI3 phosphorylate PIP2 to PIP3
PIP3 - a phospholipid - contains a PH domain which enables it to recruit proteins to the phospholipid bilayer. PIP3 recruits PKB to plasma membrane and activates it.
150
What are the functions of PKB on the plasma membrane?
Protein synthesis in muscle
Glucose transport and lipid metabolism in fat cells/lipocytes.
Glycogen metabolism in liver.
151
What are PIP2 and PIP3? Give full names.
Phospholipids.
PIP2 - Phosphatidylinositol 4,5-bisphosphate.
PIP3 - Phosphatidylinositol 3,4,5-trisphosphate.
152
What are associated TKs?
Tyrosine kinases which are not intrinsic to the receptor but associated with it.
153
Name the classes of cell surface receptors in ascending order of response time.
Ligand-gated ion channels
GPCRs
Enzyme-linked receptors
