M and R Flashcards
(320 cards)
1
Q
What are the general functions of membranes?
A
Selective permeable barrier enclosed environment Communication recognition of signaling molecules signal generation
2
Q
What are some of the specific functions a membrane can have ?
A
Interaction with adjacent cells absorption or secretion changing shape for transport synapses electrical signal conduction
3
Q
Describe the composition of a plasma membrane
A
40% lipid
60% Protein
1-10% carbohydrates
4
Q
How are plasma membranes stabilised?
A
H bonds with h2o
5
Q
Give an example of a phospholipid
A
Phosphatidylcholine
6
Q
Give an important property of phospholipid molecules
A
Amphipathic
7
Q
How are phospholipid molecules named?
A
By their head
8
Q
How can chain length of phospholipid molecules vary ? What are the most common lengths?
A
C14-C24
Most common C16 and C18
9
Q
Describe the structure of a phospholipid
A
Glycerol backbone, 2 FAs with phosphate group and head
10
Q
What is a plasmalogen? Give an example of one
A
Lipid not based on glycerol eg sphingomyelin
11
Q
What is a glycolipid?
A
Lipid containing sugar
12
Q
What are the two types of glycolipids?
A
Cerebroside - contain a sugar monomer
Ganglioside- contain a sugar oligosaccharide
13
Q
What movements are lipid able to do in a bilayer?
A
Flip flop
Rotation
Lateral drift
Flexion
14
Q
A double bond in a phospholipid has what effect?
A
Introduces a kink reducing packaging and therefore increasing fluidity
15
Q
How can a protein move in a bilayer?
A
Rotation. lateral drift and conformational change
16
Q
What type of movement can a lipid do but not a protein in a plasma membrane?
A
Flip flop - requires too much energy for the hydrophobic and hydrophilic moieties to swap.
17
Q
Describe an integral protein
A
Hydrophobic interactions with membrane - has at least one transmembrane domain
18
Q
Describe a peripheral protein
A
Held in place by electrostatic interactions or H bonds - no transmembrane domain
19
Q
What evidence is there for proteins ?
A
Freeze fracture
Fractionalization and SDS page
Specificity of function
20
Q
Why do proteins have reduced movement than lipids?
A
Tethering to cytoskeleton
Aggregates
Lipid mediated effects - areas of low cholesterol
Basolateral junctions
21
Q
Where would you find the cytoskeleton?
A
Cytostolic face of membrane
22
Q
Describe spherocytosis anemia
A
Spectrin depleted by 40-50% leading to spherical shaped RBCs
23
Q
Describe eliptocytosis
A
Defect in spectrin meaning they are unable to form tetrameres leading to fragile ellipoid cells
24
Q
What is topology?
A
Mechanisim of inserting proteins meaning proteins have very specific orientation in the membrane- membranes are therefore asymmterical.
25
What proportion of a membrane is cholesterol?
45%
26
How does cholesterol stabilise the membrane ?
Through H bonds
CHOLESTEROL ABOLISHES THE ENDOTHERMIC PHASE TRANSITION OF THE LIPID BILAYER
The sterol ring decreases packaging and increased fluidity
The long tail reduces chain motion decreasing fluidity
27
What types of molecules are able to easily pass through the bilayer?
Hydrophobic - oxygen, carbon dioxide, nitrogen and benzene
| Small uncharged polar molecules - water, urea, and glycerol
28
What molecule cannot pass through the bilayer?
Ions
| Large uncharged polar molecules
29
What are the uses of proteins in the bilayer?
Maintain ionic composition
Maintain cell volume
Maintain pH
Concentration of metabolites and anabolites
Remove waste products
Generation of ionic gradients for function
30
What does diffusion depend on?
Gradient and permeability
31
What three methods of transport are there when using a protein?
Uniport
Antiport
Symport
32
What is the problem with transport of molecules using proteins ?
They are saturatable
33
Give the extracellular concentration of Na ions
145mM
34
Give the extracellular concentration of Cl ions
123mM
35
Give the extracellular concentration of Ca ions
1.5mM
36
Give the extracellular concentration of K ions
4mM
37
Give the intracellular concentration of Na ions
12mM
38
Give the intracellular concentration of Cl ions
4.2mM
39
Give the intracellular concentration of Ca ions
10-7M
40
Give the intracellular concentration of K ions
155mM
41
Describe and give the properties of the Na+ pump
3 sodium out
2 K in
Uses one ATP
Provides the concentration gradient and therefore energy for lots of secondary active transports
42
Describe the NCX transporter
sodium calcium exchanger
1 calcium out for 3 sodium in
Low affinity high capacity
Electrogenic
43
Describe the PMCA
Plasma membrane Ca ATPase
One calcium out for one H in
Brings in H to increase electrochemical efficiency
High affinity low capacity
44
Describe the SERCA
Sarco(endo)plasmic reticulum Ca ATPase
One calcium out for one H in
located on ER - creates store of Ca
45
Describe the NHE
one H out for One sodium in
| extrudes acid using NA gradient - role in pH conc
46
Describe the AE
Anion exchanger
Bicarbonate out and Cl in
Extrudes base and electrochemically neutral
47
How do proteins help control cell volume?
Movement of osmotically active ions or organic osmolytes - h20 follows
48
How do proteins help control cell pH?
Using Na gradient
| Extrude / influx acid or base
49
What is the membrane potential ?
Electrical potential different across a membrane controlled by movement of ions
-20--90mV
50
What is the equilibrium potential ?
The potential difference across a membrane that is selectively permeable to only that ion- electrical chemical gradient equals concentration gradient leading to no net movement
51
How do you calculate the equilibrium potential for an ion?
Use of the Nernst Equation
| E= 61/Z log 10 (conc out/ conc in)
52
How is the resting membrane potential brought about?
Membrane selectively permeable to K+
K+ down concentration gradient and in down chemical gradient but anions cannot follow making cell negative compared to outside.
Na pump has minor role but is mainly used to created gradients
53
What types of gating are there?
Ligand - Fast ( intrinsic ion channel) slow ( GPCR)
Mechanical
Voltage
54
Give four properties of an AP
All or nothing
Only occur if reach threshold
Distinct signals
Propagated without loss of amplitude
55
Define depolarisation
Cell interior less negative
56
Define hyperpolarisation
Cell interior more negative
57
During the AP which ions conductance changes rapidly and which one slowly
Na - quickly
| K- Slowly
58
What type of feedback is involved in an AP?
Postive
59
Describe the channel and ion channels leading to depolarization and then repolarisation?
Na channels open leading to Na entering the cell which increases the number of Na channels open and therefore the influx of Na into the cell. This depolarises the cell.
Depolarisation opens K channels leading to influx of K into the cell and causes inactivation of Na channels stopping the Na influx resulting in repolarisation.
60
What happens during the absolute refractory period ?
All Na channels are inactivated- excitatory of cell is at 0
61
What happens during the relative refractory period?
Na channels are recovering- excitability returns to normal as number inactivated decreases
62
Describe accommodation
Constant sub threshold stimulus leads to more and more Na channels in the inactivated state meaning a larger stimulus for AP to be generated.
Eventually AP cannot be generated
63
Describe the structure of a Na channel ?
1 subunit = 4 domains = 1 functional protein
| 6 transmembrane domains - S4 channel voltage sensor- stimulated by change in transmembrane voltage
64
Describe the structure of a K channel?
1 subunit = 1 domain = 1/4 functional protein
| Need 4 subunits
65
What is the length constant?
Distance it takes for initial signal to fall by 37% of original amplitude
66
What affects the length constant?
Diameter - larger = faster
Resistance - higher = faster
Capacitance - lower = faster
67
What is the effect on transmission of myelination? Why?
Quicker at larger axon diameter due to saltatory conductance
68
What effect does myelination have on resistance and capacitance ?
Increased resistance
| Decreased capacitance
69
Where is high density of ion channels found in a myelinated neurone?
At nodes of ranvier
70
Describe the consequences of MS
Demyelination of neurones leads to a decreased length constant
Initially - total blockage of signal
Later - slower conductance as channels spread along the axon
71
How do you calculate unmyelinated neurone speed?
Proportional to square root of diameter
72
What is the maximal speed of an unmyelinated neurone?
20ms-1
73
How do you calculate the speed of a myelinated neurone?
Proportional to diameter
74
What is the maximal speed of an myelinated neurone?
120ms-1
75
At what point does speed in myelinated neurone equal that of unmyelinated?
1mm
76
Describe neurotransmitter release?
Ca entry though Ca channels bind to synaptotagmin
Vesicles brought close to membrane
Snare complex make a fusion pore
Transmitter released through this pore
77
What heads can you find on a phospholipid? What property do they all have ?
Choline, amine, amino acid, sugar
| All polar
78
Describe the formation of the bilayer?
Amphipathic molecules form bilayer spontaneously in h20 driven by VdWs between hydrophobic tails
Structure is then stabilised by non covalent forces ; electrostatic and H bonds between hydrophilic moeites and interactions between hydrophillic moeites and h20
79
How are peripheral protiens removed?
pH or ionic strength
80
How are integral proteins removed?
Agents that compete for non polar interactions with bilayer
81
How is the orientation of proteins in the membrane determined?
Protein synthesis determines this with addition of highly hydrophobic stop transfer sequence. When protein is being translated and fed into ER lumen. The stop signal will remain in the ER once it has been translated - rest of the protein is translated in cytoplasm and protein will then span the membrane.
82
Give the properties of the stop transfer sequence
18-20 AA
| Hydrophobic smaller uncharged AAs
83
What is a hydropathy plot? What are the axis?
y= hydropathy index
x= aa number
Shows how hydrophobic/ hydrophilic an AA sequence is
Can work out the number of TMDs a protein has
84
Define facilitated diffusion
Permeability of membrane to a substance is determined by specific proteins in the bilayer - modes include carrier molecules and channel proteins
85
What substance inhibits the Na pump?
Oubain
86
What happens to the NCX in ischaemia?
Decreased ATP so no Na pump leading to an increase in Na conc in the cell so the NCX reverses drawing Ca into cell.
87
What control is there on the NHE?
Activated by growth factors and inhibited by amiloride
88
Describe bicarbonate reabsorption in the proximal tube?
Na pump removes Na- NHE can therefore pump Na from the lumen into cells along gradient in exchange for H ions - H into lumen and picks up HCO3- bringing into cell.
Used to retain base for buffers
89
What are aquaporins?
Allow h2o to move increased easily through membrane - inclusion in membrane in kidney epithelial cells stimulated by ADH increasing water reabsorption
90
Describe loop diuretics ?
Block Na uptake in thick ascending limb of loop of henle
91
Describe amiloride
Potassium sparing diuretic acts on both ENAC and proximal NHE tubules to prevent Na reuptake
92
Describe the effects of excess aldosterone
Up regulate ENAC and NHE to increase Na uptake - contribute to hypertension
Treated by spironolactone
93
Describe glucose uptake
SGLUT1 - Na and glucose mover through faciliated diffusion- using conc gradient from Na pump
GLUT transport moves glucose from cell to blood stream
GLUT 1&3 found throughout the body - maintains basal level
GLUT 2 found in hepatocytes and pancreatic b cells
GLUT 4 found in striated muscle and adipose cells - insulin stimulates up regulation
94
How is it maintained that glucose never moves back into the lumen of the vessels from cells ?
Glucose is quickly converted into glucose-6-phosphate
95
What type of molecules move via passive transport?
Non polar molecules
96
How does rate change with changing the concentration gradient in passive transport?
Rate increases linearly with increase conc gradient
97
Describe the difference between active transport and other types of transport
Requires energy from ATP hydrolysis/ electron transport/ light
Against unfavorable conc and or electrical gradient
98
Describe the mitachondrial uniporter
High conc to buffer when potientally harmful- one ca in for breakdown of one ATP
99
Explain the issue with transporters in cystic fibrosis
Transport of Na of cell by Na pump allows NKCC2 channel but faulty CFTR protein leads to accumulation of Cl- in cell meaning water moves into cell via osmosis and viscous mucus in lumen
100
Explain the issue with transporters in diarrhoea
CFTR over activated by phosphorylation PKA- Cl- excessively transported into lumen water then follows.
101
In a 70kg male how much water is there? What is the breakdown of this ?
42L
Intracellular 28L
Extracellular 14L - interstitial 9.4L, plasma 4.6L
102
What would happen if there was a sudden change in Na levels ?
increase would lead to peripheral oedema or decrease would lead to shrinkage of interstitial space and blood volume --> organ misfunction
103
How is resting membrane potiental expressed?
Potiental inside the cell relative to outside
104
How can you measure a membrane potential ?
Using a very fine micropipette that can penetrate the cell and is filled with conducting solution KCl
105
What is the resting membrane potential of nerve cells?
-50--75mV
106
What is the resting membrane potential of smooth muscle cells?
-50mV
107
What is the resting membrane potential of skeletal / cardiac muscle ?
-80--90mV
108
Why is the resting membrane potential not equal to Ek of potassium?
Other ion channels are open
109
What does changing the permeability of K have on the membrane?
Changes Ek therefore changes resting potential.
110
What ions cause depolarisation of a membrane ?
Na and Ca
111
What ions cause hyperpolarisation of a membrane?
Cl and K
112
Describe fast synaptic transmission
Receptor is also an ion channel
Depolarising transmitter open channels with a positive reversal potential leading to excitation in cells causing excitatory post synaptic potential
Hyperpolarising transmitter open channels with -ve reversal potentials leading to an inhibitory post synaptic potential.
113
Describe slow synaptic transmission
Signal leads to channel being opened via a GTP binding protein.
114
Define an action potential
Change in voltage across a membrane. they are dependent on ionic gradient and relative permeability of the membrane. Generated by an increased permeability to Na in the membrane leading to movement towards Ena
115
What happens to other channels during an action potential?
open or close brought on by a conformational change
116
Why does the cell go into a state of hyperpolarisation after depolarisation in an AP?
Voltage gated k channels open therefore increased conductance of K
117
Describe the actions of procaine and its usage
Topical anaesthetic for medicine and dental surgery- vasoconstrictor and increases quality of anaesthetic.
Binds and blocks Na channels meaning AP cannot rise
Blocks conduction small myelinated axon, non myelinated axon and large myelinated axon so SENSORY BEFORE MOTOR
2 pathways
hydrophobic - pass through membrane becoming charged
hydrophilic- use dependent
118
Describe propagation of an action potential
Change in membrane potential at one part of the membrane affects adjacent sections of axon
local current causes spread of current
conduction velocity determined by how far axon current can spread
AP initiated at site of depolarisation
119
How does high membrane resistance lead to high conduction velocity?
Number of channels open - lower resistance increased channels open and more loss of local current across membrane limiting spread of current
120
How does low membrane capacitance lead to high conduction velocity?
Capacitance is the ability to store charge - high capacitance more current to charge and cause a decrease in spread of local current
121
Why does large axon diameter lead to high conduction velocity?
Decreased cytoplasmic resistance
122
Describe the composition of myelin
40% h2o
Dry mass
70-85% lipid and 15-30% protein
123
Which neurones is it easier to stimulate using electrodes and why?
Myelinated neurones as decreased capacitance
124
When does myelination start during development and when does it finish?
4th month of development and continues into 1st year of life
125
How long does regeneration in PNS take ?
1-3mm
126
Where are L type calcuim channels found?
Lungs, muscle and neurones
127
What chemical blocks L type calcuim channels?
Dihydropyridines
128
What types of calcuim channels are found in the heart?
R and T
129
Describe the structure of calcium channels ?
Very simillar to Na channels
| Extra proteins enabling correct regulation including glycosylation and phosphorylation sites
130
What are the blockers of nACHr?
Competitive and non competitive
131
Describe and give an example of a competitive blocker on nACHr?
Tubocurarine
Fits where ACH does - over come by increasing Ach conc
same amount of Ach will cause less depolarisation so may not reach threshold
132
Describe and give an example of a non competitive blocker on nACHr?
DEPOLARISING BLOCKER eg succinycholine
maintains depolarisation inhibits Achesterase
Na channels are inactivated and receptors desensitised.
sodium channels cannot activate adjacent ion channels as they are inactivated leading to MEPP - mini end plate potentials being activated.
133
What are MEPP?
mini end plate potentials - small random spontaneous release of vesicles causing a small amount of neurotransmitter being released
134
Describe myasthenia gravis and the treatment
nAchR receptors activated by target antibodies causing weakness and a reduction in end plate potentials amplitude
Treat with AchEsterase
135
What is ca needed for?
Control of fertilisation, proliferation, secretion, neurotransmitter, metabolism, contraction, memory , apoptosis and necrosis.
136
What are the advantages and disadvantages of maintaining the large gradient between Ca conc in and outside a cell?
Advantage - changes in conc occur rapidly with little Ca movement
Disadvantage - ca leads to loss of regulation and death
137
How is the large gradient in Ca set up?
Relative impermeability of the plasma membrane
Ability to expel Ca across the membrane
Ca buffers
Intracellular stores ( rapidly releasable and not)
138
Explain the activation of CaATPase?
Increased Ca conc
Ca binds to calmodulin
Ca- calmodulin complex binds to ATPase and ATPase removes Ca
139
What effect does buffers have on the ability of ca to diffuse?
Decrease as diffusion dependent on conc of binding molecule and level of sat
140
How is release from intracellular storage of calcium mediated?
By GPCRs activating Gaq which binds to phospholipid PIP2 releasing IP3 which binds to SERCA triggering release
CICR- Ca binds to ryanodine receptors on side of S/ER triggering release of increased Ca
141
In what organ is CICR very important and why?
Cardiac myocytes for coordinated powerful contraction- early depolarisation also allows NCX to reverse leading to increased Ca into the cell
142
Where is the non rapidly releasable store of Ca in the cell?
Mitachondria
143
When does uptake into non rapidly releasable ca stores occur?
When Ca conc high and in normal conditions to create microdomains
144
What is the function of Ca uptake to the mitachondria?
Ca buffering
regulate pattern and extent of signalling
stimulation of mitachondrial metabolism ( increased Ca increased Met increased ATP )
Role in apoptopic cell death
145
Describe ca store refilling
Termination of signal
Ca is recycled using store operated channels based on depleted signal - specific proteins interact following depletion to activate channels (STIM and ORAI)
146
What chemicals may be used during chemical signals?
Hormones, neurotransmitters and local chemical mediators
147
Define a ligand
Any small molecule that binds specifically to a receptor site
148
define a agonist
a ligand that produces activation of a receptor
149
define an antagonist
a ligand that combines with a receptor site without causing activation
150
define a partial agonist
agonist that stimulates a receptor but are unable to elicit maximal cell response
151
define a receptor
a molecule that specifically recognises a ligand or family of ligands and in response to binding brings about regulation of a cellular process.
UNBOUND THEY ARE FUNCTIONALLY SILENT
152
define an acceptor
operate in absence of a ligand - binding of a ligand has little or no effect
153
How can signaling between cells be done?
Secreted molecules or siganlling via plasma membrane bound molecules using adhesion molecules
154
Define paracrine
local chemical mediator secreted into interstitial space and bind with adjacent cells causing a whole tissue response
155
Define endocrine
hormone released into blood stream and arrives at distal site to cause a response
156
Where are hydrophilic molecules receptors?
On the cell surface
157
Where are hydrophobic molecules receptors ?
Intracellular - nucleus or cytoplasm
158
Give some simillarities between receptors and enzymes
specific sites
binding governed by shape of binding cleft
binding is reversible
specificity of binding confers specificity to regulation of process involved
binding induces a conformational change and change is activity of molecule
no chemical modification of ligand in binding
159
Give the differences between receptors and enzymes
Affinity - receptors higher affinity
ligand binded to receptor site is not modified chemically whereas substrate bound in an enzyme if modified in chemical reaction catalysed by active site
160
How are receptors classified?
Specific physiological signalling molecule recognised
| Affinity to a series of antagonists
161
Explain the process of signal transduction by membrane bound ion channel
Membrane bound ion channels- binding leads to conformational change and opening of gated ion channels permitting flow of ions eg nAchR, GABA, gylcine and glutamate
162
Describe the structure of a membrane bound ion channel
Classic -Pentameric structure - 4 TMDs- 1 lining pore, 2 bind ligand and each has charge attracting ions
SEE DIAGRAM
Non classic - eg IP3
163
Explain the process of signal transduction by membrane bound receptor with integral enzyme activity
Ligand binds to extra cellular domain of receptor activity causing conformational change activating intrinsic enzyme activity contained within the structure of the receptor
eg growthe factor receptors for insulin, EGF and PDGF linked to tyrosine
164
Explain tyrosine kinase linked receptors
Binding of hormone to binding sites activates protein kinase activity in cytoplasmic domain which autophosphorylates tyrosine residues on cytoplasmic domain of receptor. This is recognized by transducing proteins or directly by enzymes containing phosphotyrosine recognition sites. The enzyme is then activated by phosphorylation or allosterically.
165
Explain the process of transduction via membrane bound receptors which couple to effectors via GTP binding regulatory proteins to enzymes or channels
Receptor bindinf results in a conformational change which activates a GTP/GDP exchange in GTP binging regulatory proteins
eg mAchR and all adreonceptors
166
Describe the structure of a GPCR
7 TMDs
N cytoplasmic C in cell part of G protien coupling domain
LOOK AT SHEET
167
Describes signal transduction via intracelllular receptors
Binds to monomeric receptors in cytoplasm or nucleus
Stabilized in resting state by HSP or chaperone proteins - activated receptor dissociates from chaperone protein in nucleus where it binds to control regions in DNA defined by specific sequences leading to regulation of gene expression
168
Describe by the structure of intracellular receptors
C region- binding domain
Middle - DNA binding domain
N region - nothing
169
How is amplification achieved?
Cascade
170
What in lay mans terms is receptor mediated endocytosis?
Membrane internalisation
171
What cells can perform phagocytosis?
neutrophils and macrophages
172
Explain the process of phagocytosis?
Particles bind to receptor in plasma membrane, cell extends pseudopod to permit further interactions and membrane evagination and particle internalisation via membrane zippering mechanism.
Internalised phagosome then fuses with a lysosome forming a phagolysosome and particle is degenerated
173
Define pinocytosis
invagination of plasma membrane to form lipid vesicle permits uptake of impermeable extracellular solutes and retrieval of PM.
174
What are the two types of pinocyosis
Fluid form and receptor mediated endocytosis
175
Define receptor mediated endocytosis
Selective internalisation of molecules into cell by binding of molecules to specific cell surface receptor
176
Describe the uptake of cholesterol by receptor mediated endocytosis
LDLs bind to receptors for ApoB on clathrin pits which form spontaneously these are invaginated and pinch of the PM to form coated vesicles. The vesicles are uncoated by an ATP dependent process and then fuse with larger smoother vesicle endosome. In the endosome the receptor and LDL dissociate. The transmembrane receptors is sequestered off to a domain within endosome membrane budding off as a vesicle to be recycled. LDL is then degraded
177
Describe an LDL particle
Originates in the liver
core of cholesterol molecules esterified to FAs surrounded by a lipid monolayer containing phospholipids cholesterol and ApoB.
178
Which cells express an ApoB receptor
Those requiring cholesterol
179
Why does the receptor and ligand dissociate in the endosome?
Endosome ph 5.5-6 maintained via ATP dependent proton pump
180
Describe the structure of of clathrin coated pit
Minimum stucture - triskeleton ( 3 legged) contain clathrin and 2 light chains
Triskeletons associate to form basket structure making hexagon and pentagon structures
181
Describe the uncoating of a clathrin pit
Carried out by an ATP dependent uncoating protein which binds and stabilises the freed coated proteins
182
How is the clathrin pit attached to the PM and what is its function?
By a number of integral membrane adapter proteins which form associations both with clathrin and receptors.
Locate receptors over the clathrin pit
183
Describe the defects that may be present in the receptors in a patient with hypercholesterolaemia?
Receptor deficiency- prevent expression of LDL receptor
Non functional receptor
Receptor binding normal - no internalisation due to deletion of C terminus meaning no interaction with a clathrin pit
184
Describe iron uptake
2 Fe3+ ions bind to apotransferrin forming transferrin which binds to receptors at neutral pH and is internalised. At acidic pH iron is released by apotransferrin remains bound to the receptor- complex is sorted in CURL for recycling back to PM.
Ligand and receptor are recycled
185
Describe uptake of occupied insulin receptors
Only over clathrin pits when bound as binding induces a conformational change so now recognised by clathrin pits. In CURL insulin remains bound to receptor and complex is degraded by lysosome
Ligand and receptor are both degraded
186
Why is it beneficial that both the ligand and the receptor are degraded in insulin receptor uptake ?
Allows for the reduction in number of insulin receptors on membrane desensitising the cell to continues high levels
187
Explain the process of transcytosis
Ligands remain bound to receptors and are transported accross the cell
188
Give and explain an example of transcytosis
Maternal immunoglobulins to foetus via placenta
Transfer of immunoglobulin A from circulation to bile to liver - during this receptor cleaved resulting in release of immunoglobulin with bound secretory component from receptor
189
What two pathogens take advantage of receptor mediated endocytosis?
Chlorea and diptheria
190
How do pathogens take advantage of receptor mediated endocytosis?
Binding to cells by fotuitous association with cell receptors and entering cells via pits - unfolding hydrophobic domains in membrane fusion proteins at lower pH. They they insert the membrane fusion proteins into endosome membrane leading to this fusing with the membrane and release of the genomic RNA into cell cytoplasm. They then use the host machinery to replicate RNA and caspid proteins to bind new viruses at cell membrane.
191
Why must signal transduction occur?
Most signals cannot enter cells to cause a response so must activate a protein on the cell surface and use this to transduce into the cell.
192
How do G proteins alter activity of effectors?
Via activation of guanine nucleotide binding proteins
193
What are G proteins responsible for?
Muscle contraction, stimulus secretion coupling, catabolic and metabolic processes , light/smell and taste perception
194
Describe the structure of G proteins
Same generic heteromeric structure made up of 3 subunits ( alpha, beta and gamma)
Beta and gamma bind each other so tightly they can be classed as one unit
195
Describe the method of activation and termination of activation of G proteins
1) Basal state G protiein present at inner face of PM predominately in heteromeric form
2) Alpha subunit binds guanine nucleotide of GTP to hydrolyse to GDP
3) Activated receptor has high affinty for G protein and protein -protein interactions.
GDP released from alpha subunit and replaced by GTP
4) Binding of GTP reduced affinity of aplha subunit for receptor and beta-gamma subunit. Therefore these are released to interact with effectors
5) Effector interactions is terminated by intrinsic GTPase activity of alpha subunit turning GTP back to GDP leading to increased affinity again.
196
Why can a G protein be classed as an on off switch?
On - receptor facilitated GTP/GDP exchange
| Off- determined by time taken for GTP hydrolysis ( timer function)
197
How does cholera interact with a G protein?
Deactivation of Gs protein mediated signalling inrreversibly- Gsa subunit uncouples
198
How does pertussis interact with a G protein?
Prevents Gi protein activation by GPCRs- irreversibly
199
What does cholera and pertussis interaction with G proteins have incommon?
ADP- ribosylate specific G proteins
200
What are the signalling cascade three components ?
Receptor
GPCRs
Effector molecule (ion channel or enzyme )
201
What is the consequence of activation of Gs ?
Increased adenylyl cyclase leading to lipolysis and glycogenolysis
202
What is the consequence of activation of Gq ?
Increased phospholipase C leading to Smooth muscle contraction
203
What is the consequence of activation of Gi?
Decreased levels of adenylyl cyclase and stimulation of k channels leading to slowing of cardiac pacemaker
204
What is the consequence of activation of Gt?
Stimulation of cyclic GMP phosphodiesterase leading to visual excitiation
205
What does cyclic GMP phosphodiesterase do ?
hydrolyses cyclic GMP to 5' GMP
206
What does phospholipase C do?
PIP3 --> InsP3 and DAG
207
Mutations to GPCRS cause what?
disease through loss or gain of function
208
What is retinitis pigmentosa?
Loss of function mutation to rhodpsin
209
What is nephrogenic diabetes insipidus?
Loss of function to V2 vasopressin receptors
210
What is familial male precocous puberty?
Gain of function mutation to LH receptor
211
What is the function of adenylyl cyclase ?
Hydrolyses cellular ATP to generate cyclic AMP which interacts with specific protien kinases to phosphorylate a variety of other proteins within a cell
212
What is the effect of increased adenylyl cyclase?
Glycogenolysis, gluconeogenesis, lipolysis
| Relaxation of variety of types of smooth muscle, positive inotrophy and chronotrophy
213
What is the function of phospholipase C?
Membrane phospholipid PIP to IP3 which interacts with specific intracellular receptor on ER to allow Ca ions into cytoplasm
214
Describe the deactivation pathways of GPCRs?
While activated receptor susceptible to variety of kinases that phosphorylate the receptor and prevent it activating further G proteins - desensitisation phenomenon
Lifetime of alpha GTP may be limited by cellular factors that interact GTPase
Basal states are favoured
Enzymatic cascades activated downstream - act to oppse GPCRs effect
215
Explain the regulation of chonotrophy of the heart?
Rate of AP generation can be affected by Ach release to M2 receptors which increase potassium channel opening leading to hyperpolarisation slowing intrinsic firing rate resulting in negative chronotropic effect.
216
Explain the regualtion of inotrophy of the heart?
Circulating adrenaline and sympathetic innervation B1 receptors activated causes increase open probability of voltage operated calcuim channels.
Gs also indirect effect by increasing cAMP --> PKA --> phosphorylation and activation of VOCC leading to influx of Ca
217
Explain the regulation of arteriolar vasoconstriction
NA on alpha 1 receptors to stimulate phospholipase C and IP3 production via Gq- IP3 release on ER ca leading to contractile response
218
Explain the regulation of modulation of neurotransmitter release?
Presynaptic GPCRs can influence the release eg pre synaptic u-opoid receptors stimulated by endogenous opoids or analgesics to couple Ga1
Gby subunits liberated interact with VOCC to decrease Ca release
219
Where do drugs bind to ?
Receptors or proteins - GPCRs and enzymes most common
220
What concentration is important in determining drug action?
Concentration of drug molecule around receptor
221
When do drugs have the same concentration of drug molecules?
Drugs with equivalent molar conc NOT equivalent conc by weight
222
How many particles does 1M contain?
6x10^23
223
What is drug receptor binding governed by?
Association and dissociation rates - related to concentration of reactants and products
224
What must a substance have to be an agonist?
Both affinity and efficacy
225
What does an antagonist have in terms of affinity and efficacy?
ONLY affinity
226
What is affinity?
Likelihood of ligand binding to its target.
| Reciprocally measured by dissociation constant
227
What is efficacy?
Likelihood of activity - governs receptor activation
228
What is Bmax?
Max binding capacity- information about receptor number
229
What is Kd?
Dissociation constant ( measure of affinity)- conc needed for 50% occupancy
230
What does a small Kd show?
Increased affinity
231
What is Kd known as if it is determined pharmalogically?
Ka
232
What does a conc response curve show?
Response in cells/ tissue
233
What does dose response curve show?
Response in whole body
234
What is E50?
Effective [ ] giving 50% maximal response - measure of potency
235
What is potency?
Combination of affinty, efficacy and number of receptors - tissue dependent factors
How good a drug is at generating response measured by EC50.
236
What is I50?
Inhibitory drugs - inhibitory concentration gicing 50% of maximum inhibition
237
With the same Emax does a drug have to have the same efficacy?
No could have different affinity
238
What is asthma?
Reversible airflow obstruction and bronchiospasm
239
What is the treatment goal of asthma?
Activate B2 adrenoceptors to relax airways but avoid B adrenoceptors else where in the body
240
Describe the properties of salbutamol and salmeterol
Salmeterol - lower Kd for B2 compared to B1 therefore increased affinity- selective efficacy
Route of adminstration limits B1 affects
Salmeterol - longer acting no selective efficacy prevents b1 side effects by different affinty
241
What is the problem of giving salbutamol in a drip to a patient with a heart condition?
No selectivity so causes increased heart rate by activation of B1 receptors and therefore reduces filling of coronary vessels leading to angina symptoms
242
When are spare receptors often seen and why?
receptors that show catalytic activity as amplification in signal transduction pathway and response limited by poster receptor event
243
What is the function of spare receptors?
Increase sensitivity allowing for response at decreased conc
244
changing receptor number affects what?
Changes agonist potency - affects maximal response that can be induced
245
With increased activity what happens to the number of receptors found on a cell membrane ?
Decrease
246
What are partial agonists?
Drugs that cannot produce maximal effect even when full receptor occupancy
247
Can a partial agonist be increased potent than full agonist?
Yes - depends on tissue and biological response
248
When can a partial agonist turn into a full agonist?
Increased receptor number - still show low efficacy but sufficient receptors
249
Give a use of partial agonist
Opoids
Morphine - full agonist
Buprenorphine - partial agonist - increased affinity but decreased efficacy provides adequate pain relief but decreases respiratory depression.
Addicts still get withdrawel symptoms
250
What are the 3 types of antagonists?
Reversible competative antagonists
Irrervsible competative antagonist
Non competative antagonist
251
Describe reversible competitive antagonists
Relies on dynamic equilibrium between ligands and receptors - increased conc increases inhibition
overcome by increasing agonist conc which causes a parralell shift to R of conc response curve
EG Naxolone for opoid respiratory depression
252
Describe irreverisble competitive antagonists
Slow or no dissociation
Causes a parrallel shift to R of agonist conc response curve and at an increase conc supress maximal response - spare receptors filled by antagonist so not enough free receptors to elicit maximal response
EG Phenoxybenzamine - non selective alpha 1 blocker used in hypertension episodes of phenochromocytoma
253
Describe non competative antagonists
Allosteric binding to receptor molecules - increase or decrease effect of binding of agonist
254
Describe desensitisation
Loss of functional response usually reversible due to down regulation of receptors and uncoupling of receptor-effector molecules eg during repeated drug application
255
Define tolerance
Diminishing effect of a drug due to prolonged repeat exposure - have to give increased amounts for same effect
256
Define supersensitivity
Enhanced response of binding of agonist
257
Define tachyphylaxis
Response to a drug gets smaller when a drug is given at high doses / repeatedly
258
Describe homologous desensitisation
Receptor decrease its response to signal when agonist present at high conc
259
Describe heterologous desensitisation
Prolonged stimulation to one agonist results in desenstisation to variety of agonists
Receptor is uncoupled from cascade
260
Give some methods of desensitisation
Phosphorylation of receptor eg binding of adrenaliune to B adrenergic receptor activates G protein - while dissociated Gby subunit activates BARK a kinase which phosphorylates residues on carboxyl terminus of receptor
Receptor internalisation
261
Define pharmacokinetics
What the body does to the drug
262
What can changing receptor number do?
Changes agonist potency and affect maximal response
262
Why does binding to spare receptor have no effect one 100% effectiveness been reached ?
Lack of ability post receptor binding eg ions or cascade working at maximal capacity
263
What is orthosteric?
Binding act active site
264
Give three ways that a drug is administered? How are they altered in the body?
Oral - goes through first pass metabolism which alter the drug
Parenteral- intravenous and intramuscular which goes straight into extracellular fluid
Topical - cream into the site
265
Apart from administration what do drugs maker need to consider
Formulation - subset of oral administration
| Compliance - liquid to children
266
What is theraputic ration
Lethal dose over effective dose for half the population
267
What does an incresed theraputic ratio lead to ?
Increased therpeutic window
268
What is bio-avaliablity?
Proportion of drug reaching systemic circulation unchanged - affected by first pass effect
Only applies to thing that are administered orally
Sometimes measured as area under curve of orally taken in drug divide the injected one
269
Describe first pass metabolism
May activate or not change drug but normally inactivated reducing the oral dose decreasing bioavaliability
270
How can first pass metabolism be avoided ?
Changing administration route - eg GTN given sublingually
271
Describe drug metabolism
Most by enzymes in the liver which are inducable and inhibitable by other enzymes
272
How are drugs excreted?
Only free drug filtered by glomerulus- may be activate lay secreted by tubule cells
Passive reabsorption only occurs to non ionised - depends on drug pka and urging pH- increases blood conc
Aspirin overdose make the urine alkali to increase removal
273
What happens to a drugs half life during renal failure?
Increased
274
How are drugs transported in the body? What effect does this have on amount of response ?
Bound to carrier proteins such as albumin
| Only the free unbound drug can interact with the receptor
275
Why would you give larger concentrations of class two drugs? When is this used?
```
Given at dose greater than number of albumin binding sites - allow more of the class 1 drug to be free in the blood leading to a greater response at a lower dose
When class 1 toxic at high doses due to side effects
When class I has a high affinity to albumin
```
276
What type of drug is warfarin ?
Class 1 therefore must be careful with dose as narrow theraputic window
277
Describe first order drug elimination
Rate of elimination is proportional to drug conc
| Half life is constant
278
Describe zero order drug elimination
Rate of elimination is contact because the enzymes are saturated -happens to all drugs at high doses
Must be very careful when administering 0 order drugs as conc will increase massively as no more can be removed
279
Describe the parasympathic nervous system
```
Rest and digest
Craniosacral
Use Ach at both ganglionic neurones
Long myelinated pre ganglionic fibres short unmyelinated post ganglionic fibres
Ganglia located in tissues
```
280
Describe the sympathetic nervous system
Fight or flight
Thoracolumbar
Preganglionic Ach and post ganglionic use NA
Short myelinated pre ganglionic fibres and long myelinated post ganglionic fibres
Ganglia in para vertebral chain
281
What are the exceptions in the sympathetic nervous system
sweat glands and hair follicles are cholinergic
NANC transmitter may be released - non adrenergic non cholinergic
Sympathetic neurones to chromaffin cells in adrenal medulla are only preganglionic
282
Describe nor adrenaline synthesis
Tyrosine , DOPA dopamine to adrenaline
| Enzymes invoked tyrosine hydroxylase , DOPA decarboxylase and the Dopamine b hydroxylase
283
Describe signal termination of nor adrenaline
Uptake 1 - by Na dependent high affinity transporters
Uptake 2- 5% escapes
Within presynaptic repackaged or degradaded
284
What are NANC? Give some examples
Non adrenergic non cholinergic transmitters that may be co released with Ach or NA
Examples include- ATP, NO, 5 hydroxytryptamine and neuropeptides
285
Describe the function of chromaffin cells
Found in the adrenal medulla - sympathetic nervous innervation leads to release of nor adrenaline into the blood. They are considered only to have a pre ganglionic neurone therefore use Ach
286
What parasympathetic effects are there on the heart ? At what receptors?
Act at the atria on M2 receptors
| Causing bradycardia and cardiac conduction velocity
287
What parasympathetic effects are there on the lungs ? At what receptors?
Bronchial/bronchiolar contraction - M3
288
What parasympathetic effects are there on smooth muscle ? At what receptors?
Increased intestinal mobility /secretion M3
bladder contraction and relaxation , Penile erection and ciliary muscle and iris sphincter contraction due to NO generation
289
What parasympathetic effects are there on glands ? At what receptors?
Increased sweat/ salivary/ lacrimal secretion at M1 and M3
290
What sympathetic effects are there on the heart ? At what receptors?
Atria and ventricles
Tachycardia and positive inotrophy
on B2 receptors
291
What parasympathetic effects are there on smooth muscle ? At what receptors?
Arteriolar contraction/ venous contraction A1 or B2
Bronchiolar, intestinal and urinal relaxation B2
Bladder sphincter contracition B3
Radial muscle contraction - A1`
292
What are the basic steps in neurotransmission?
1) uptake of precursors
2) synthesis of transmitter
3) vesicular storage of neurotransmitter
4) degradation of transmitter
5) depolarisation by propagated action potiental
6) Influx of ca in response to depolarisation
7) Exocytotic release of transmitter
8) diffusion to post synaptic membrane
9) interaction with post synaptic membrane
10) Inactivation of transmitter
11) reuptake of transmitter or degradation products
12) interaction with pre synaptic
293
Explain how Ach is synthesised?
Enzyme choline acetyltransferase
From choline ( essential in the diet) and acetyl CoA in the cytoplasm.
Producing Ach and coenzyme A
294
Explain how Ach is degraded ?
Enzyme - Acetyl cholinesterase
| Produces- Acetate and choline
295
At what points could drugs be used to inhibit Ach action?
Anticholinesterases
Depolarising blocking agents
Non depolarising blocking agents
Presynaptic toxins
296
How do agents that interfere with cholinergic transmission usually act?
Interaction with cholinoreceptors or cholinesterase inhibitor to decrease rate of Ach degeneration
297
Describe the treatment of glaucoma?
Pilocarpine applied in the form of eye drops .
| Pilocarpine is a muscarinic cholinoceptor agonist
298
Give some examples of some nicotinic cholinoceptor antagonists
Those that have preferential ganglion- trimethaphan
| Neuromusclar blocking action - tubocurarine
299
Describe and name some muscarinic cholinoceptor antagonists
Hyosine - anaesthetic premedication- decreases brochial and salivary secretions, prevents reflex bronchioconstriction , reduces any bradycardia induced by anaesthetic and sedative effect
Local application of poorly absorbed muscarinc cholinoceptor antagonist- used to treat bronchoconstriction in asthmatics
Homatropine - causes pupillary dilation and paralysis of accomadation - facilatating opthalmoscopic examination
300
Give some function od cholinesterase inhibitors
Used to acutely reverse the effects of non depolarizing neuromusclar blocking agents used in anaesthesia, treatment of glaucoma and myasthenia gravis.
recently early treatment of alzheimers
301
What is the rate limiting step in the synthesis of NA?
Tyrosine hydroxylase
302
What allows the release of adrenaline into the blood?
Presence of phenylethanolamine N- methlytransferase in chromaffin cells
303
What enzyme allows conversion from dopamine to NA? Where is it found?
Dopamine B hydroxylase
| Within synaptic vesicles
304
What do the vesicular transport systems recognise ? What does this allow for?
Dopamine and Nor adrenaline allowing reuptake and recycling.
305
What are the likely side effects of non selective muscarinic Ach receptor agonist?
Decrease heart rate and CO
Increased bronchoconstriction and GI tract perstalsis
Increased sweating and salvation
306
What is a variscosity? Where are they found?
Highly branching axonal network with numerous cell like bulges- varicosity- each of which is a specialised site for Ca dependent nor adrenaline release
307
Outline the stages following an Ca dependent exocytosis release of NA
NA diffuses across the synaptic cleft and interacts with adrenoceptors in the post synaptic membrane to intiate signalling in the effector tissue
NA interacts with pre synaptic adrenoceptors to regulate processes within the nerve terminal
Only a small window to influence adrenoceptors as rapidly removed by noradrenaline transporter proteins
308
What two enzymes are involved in metabolism of non taken up NA?
Monoamine oxidase
| Catechol-O-methyltransferase
309
How can presynaptic G protein coupled receptors regulate neurotransmitter release?
Inhibiting Ca dependent exoytosis
G protein By subunit inhibits specific types of voltage gated Ca channels reducing ca influx and neurotransmitter release
310
What are the classes of drugs acting on adrenergic nerve terminals?
```
a methyl tyrosine
A Methyl DOPA
CarbiDOPA
Adrenergic blocking agents
Indirectly acting sympathomimetic agents
Uptake 1 inhibitors
```
311
Describe the mechanism of action of a methyl tyrosine
Competatively inhibits tyrosine hydroxylase - blocks synthesis of NA.
Used to inhibit nor adrenaline synthesis in pheochromocytoma
312
Describe the mechanism of action of a methyl DOPA
taken up and converted into a methyl noradrenaline by DOPA carboxylase and dopamine B hydroxylase.
Accumulates in the synaptic vesicles - released by Ca mediated exocytosis but differs from NA as preferentially activates pre synaptic a2 adrenoceptors reducing transmitter release
Exploited in hypertension
313
Describe the mechanism of action of carbiDOPA
Inhibits DOPA carboxylase in periphery but not in CNS
| Used as part of treatment for parkinsons
314
Describe the mechanism of action of adrenergic blocking drugs
Selectively concentrated in terminals by Uptake 1. They act via a variety of mechanisms, including a local anaesthetic action reducing impulse conduction and Ca2+ mediated exocytosis and repletion of NA from synaptic vesicles. Rarely used therapeutically because of severe side effects (postural hypotension).
315
Describe the mechanism of action of uptake 1 inhibitors
Comprise an important class of therapeutic agents, the tricyclic antidepressants. These agents exert their therapeutic actiosn centrally and their possible peripheral actions (e.g. tachycardia and cardiac dysrhythmias) are unwanted side effects.
316
What drugs act at cholinergic nerve terminals
* Nicotinic Cholinoceptor Antagonists
* Muscarinic Cholinoceptor Agonists
* Muscarinic Cholinoceptor Antagonist
* Cholinesterase Inhibitors
317
Describe the mechanism of indirectly acting symohomimetic agents
Structurally related to noradrenaline - weak agonists at adrenoceptors
IASA recongised and taken up into synaptic vesicles where they cause leak of NA- displacement can leak into synaptic cleft by unrelated mechanism.
Extent to leakage greatly enhanced by inhibition of noradrenaline degrading enzyme MAO.
318
Give some important uses of adrenoceptor agonists
selective b1 agonists - dobutamine- positive inotrophy and chronotrophic effect for use in circulatory shock (BUT prone to causing cardiac dysrythmias)
Selective B2 agonists - bronchoonstriction reversal in asthma
selective a1 agonist - nasal congestants - may be given in conjection with local anaesthetic injection to cause vasoconstriction and there slow spreading of anaesthetic
Selective A2 agonists - antihypertensive agents - through stimulation of inhibitory pre synaptic receptors which decrease NA release and centrally mediated action
319
Give some important uses of adrenoceptor antagonists
A adrenoceptor antagonist - cause peripheral vasodilation in treatment of peripheral vascular disease
Not hypertension as cause postural hypotension and reflex tachycardia
Selective a1 adrenoceptor antagonists used in treatment of hypertension
B adrenoceptor antagonists- hypertension, cardiac dysrhythmias, angina and MI- possible side effects bronchoconstriction, bradycardia , cold extremities, insomina and depression.
