Membranes & Receptors Flashcards
How are bilayers stabilised?
Stabilised by non-covalent forces such as: - Electrostatic and hydrogen bonding between hydrophilic moieties - Interactions between hydrophilic groups and water.
When during development does myelination begin to occur?
Four months into foetal development
What does amiloride do?
It inhibits the Na+/H+ Exchanger (NHE)
What is depolarisation?
The cell interior becomes less negative. (the opening of Na+ or Ca2+ channels)
What is potency? How can it be measured?
This is a combination of both affinity and efficacy. The number of receptors also governs potency. The EC50 (effective concentration giving 50% of the maximal response)
What is the pK of the drug?
The pH at which half of it is ionised and half not.
Most natural ligands of tyrosine kinase-linked receptors are what?
Growth factors
What are the two categories of proteins found in the lipid bilayer? (hint: where they are positioned)
-Peripheral membrane proteins - bound to the surface of membrane by electrostatic/hydrogen bond interactions -Integral membrane proteins - interact with hydrophobic regions of lipid bilayer
When is a concentration response curve used? Why is it used instead of a dose response curve?
Used in measuring a response in cells/tissues whereas a dose response curve would be used for an entire animal
What is the general composition of membranes when anhydrous?
-60% protein -40% lipid -1-10% carbohydrate
How does the pharmacological agent tubocurarine work?
It is a competitive blocker of nicotinic ACh receptors, it binds at the ACh site and keeps the ligand gated ion channel closed.
What does Bmax indicate?
Maximum binding capacity - how many receptors are available in total.
How much calcium is there in the cell and out of the cell?
Intracellular - 50-100nM Extracellular - 2mM
How is the calcium gradient set up and maintained?
-Membrane permeability to calcium controlled by open/closed calcium channels -Expel calcium out across the plasma membrane (via PMCA and NCX) -Ca2+ buffers -Intracellular calcium stores
Which two organs are responsible for elimination of drugs?
-Liver (metabolism) -Kidney (excretion)
What type of ion channel accompanies the ryanodine receptor?
Non-classical ligand-gated ion channel
Describe how sympathetic activity can lead to a positive inotropic effect.
-Activation of β-Adrenoceptors (predominantly β1) increases the open VOCCs via Gs. -Gs both interact directly with the VOCCs, and indirectly via cyclic AMP → PKA → phosphorylation and activation of VOCCs. -Influx of Ca2+ brings about a positive inotropic effect
What type of G protein do M1 receptors stimulate? What does this stimulate or inhibit?
Gq - stimulates PLC
What does the activation of a glycine receptor result in?
Membrane hyperpolarisation and decreased membrane excitability
What is the purpose of spare receptors?
Spare receptors increase sensitivity, allowing for responses at low concentrations of agonist.
How is Ca2+ removed from the cell by Ca2+-ATPase?
-Intracellular Ca2+ increase and binds to calmodulin -This Calmodulin-Ca2+ complex binds to Ca2+-ATPase and is removed
What is phospholipase C (PLC)? What is it activated by?
An enzyme that hydrolyses the membrane phospholipid (PIP2) to IP3. It is activated by Gq
Describe the uptake of Fe3+ ions by Transferrin as an example of receptor mediated endocytosis.
-In the circulation two Fe3+ ions bind to apoptransferrin to form transferrin -Transferrin binds to the transferrin receptor and is internalised the same way as LDL, via the endosome -Upon reaching the acidic endosome, the Fe3+ ions are released from the transferrin which forms apotransferrin again -Complex is sorted in the CURL where the apotransferrin is recycled
Give an example of a irreversible competitive antagonist. Explain what it does
Phenoxybenzamine is a non-selective α1-adrenoceptor blocker used in hypertension episodes in pheochromocytoma (a tumour of the adrenal gland, which causes excessive NA/Adrenaline secretion leading to vasoconstriction).
Where are phospholipids synthesised?
The endoplasmic reticulum
Which structure is favoured by phospholipids/glycolipids in water?
Bilayer
How can integral membrane proteins be removed from the lipid bilayer?
Only by using detergents that compete for the non-polar interactions in the bilayer CANNOT be removed by changes in pH or ionic strength
What is the main treatment goal when treating asthma? What receptors are targeted?
The treatment goal is to activate β2-adrenoceptors to relax the airways
What does the term amphipathic molecule mean?
Molecules that contain both hydrophillic and hydrophobic parts
Describe the process of extracellular recording? How can it be used to measure conduction velocity?
Electrodes are used to raise the membrane potential to threshold to generate an action potential. By recording changes in potential between the stimulating (Cathode –‘ve) and recording (Anode, +’ve) electrodes along an axon, conduction velocity can be calculated.
Approximately what ratio is there of cholesterol molecules to phospholipid molecules in plasma membranes?
1:1
What does adenlyl cyclase do?
This enzyme hydrolyses cellular ATP to generate cyclic AMP
What structure do most drugs bind to?
Proteins
How is intracellular Ca2+ elevated?
-Ca2+ influx across the plasma membrane (VOCC and receptor operated ion channels) -Ca2+ release from ‘rapidly-releasable’ stores (GPCRs and CICRs) -Ca2+ release from ‘non-rapidly releasable’ stores (from mitochondria)
How is bicarbonate reabsorbed by the proximal tubule of the kidney?
The intracellular Na+ is kept low so NHE has enough to pump into the proximal tubule lumen. The H+ in the lumen joins with bicarbonate and brings it back into the cell.
Where do LDL-receptors form on the plasma membrane specifically?
Localised in clusters over clathrin coated pits (form spontaneously, just like clathrin cages)
What is the effect of having double bonds in the fatty acid chains of phospholipids?
The ability of the phospholipid to form two-dimensional crystals decreases
Why can an action potential not go backwards on itself?
It is unidirectional as the area that had just fired the AP is refractory
What is the function of SERCA?
A high affinity, low capacity antiport that uses ATP to accumulate Ca2+ into the SR/ER in exchange for H+
Give as many members of the G protein receptor family as you can
-Adenocorticotropin hormone (ACTH) receptor -Angiotensin II (AII) receptor -Dopamine receptor -Gamma aminobutyric acid receptor B (GABABR) -Muscarinic acetylcholine receptor (mAChR) -P2y-purinoceptor (ATP) -Substance P receptor
What are the approximate intra and extracellular concentrations of potassium?
Intracellular - 160mM Extracellular - 4.5mM
Define the antagonist
Any molecule that binds specifically to a receptor site and binds without causing activation i.e. blocking.
What do inhibitory postsynaptic potentials do to the membrane?
Render the membrane less electrically excitable
Define the term efficacy in relation to pharmacology
Likelihood of receptor activation
What is active transport?
The transport of ions or molecules against an unfavourable concentration and or/electrical gradient, requiring energy from the hydrolysis of ATP.
How might peripheral proteins be bound to plasma membranes?
-Electrostatic interactions -H-bond interactions -Disulphide bond interactions
What is the function of AE?
The anion exchanger pushes out HCO3- and takes in Cl- acidifying the cell resulting in regulation of its volume.
What are the two types of refractory period? What is the difference between them?
-Absolute refractory period - all of the Na+ channels are inactivated (well mostly) -Relative refractory period - Na+ channels are recovering from inactivation, excitability returns to normal as the number of channels in the inactivated state decreases
Suggest two drugs which exhibit zero order kinetics.
-Alcohol -Phenytoin
What does G-protein interaction occur predominantly with?
The third cytoplasmic loop and the intracellular C-terminal domain of G-protein-coupled receptors
What does the binding of ouabain do? Where does it bind?
Ouabain binds to to the alpha sub-unit of Na+/K+-ATPase (where K+, Na+, ATP binds aswell) it inhibits the pump.
How do local anaesthetics (like procaine) work?
They act by binding to and blocking Na+ channels, stopping action potential generation
What is accommodation?
The process by which an action potential is not created due to a stimulus taking too long to reach the threshold (which is becoming more positive)
What are co-transporters? What are the two types?
Membrane transporters that transport more than one molecule. The two types are symports and antiports
What are LDL molecules made up of?
-Core of cholesterol molecules esterified to fatty acid -Surrounded by a lipid monolayer containing phospholipids, cholesterol and a single protein species, Apoprotein B
What does the displacement of drugs from binding sites cause?
Protein binding drug interactions
The influx of which ions can cause cell swelling?
Influx of Na+, K+ and Cl-
How are bilayers formed?
Formed by Van der Waals forces between the hydrophobic tails
What is required to release vesicular stores of Ca2+ required for contraction in skeletal muscle?
Physical coupling between voltage-sensitive Ca2+ channels and ryanodine-sensitive calcium channels in the sarcoplasmic reticulum
What three ways can hydrophilic signalling molecules bring about signal transduction?
-Integral ion channels -Integral enzyme activity -Coupling to effectors through transducing proteins
Why can Receptor-Mediated Endocytosis Mode 3 be a model for the development of Type II Diabetes?
This can result in desensitivity as there is less and less receptors present
At high temperatures how does cholesterol stabilises the fluidity of the membrane?
Forms H-Bonds with other phospholipids which reduces the chain motion of the membrane lipids which in turn reduces fluidity
The nicotinic acetylcholine receptor is mainly permeable to which three ions?
-Na+ (this predominates) -K+ -Ca2+
During membrane protein biosynthesis, what releases the arrest of the synthesis?
Interaction of signal recognition particle with the endoplasmic reticulum docking protein releases arrest of biosynthesis.
What are glycolipids?
Lipids with a carbohydrate attached to them
Describe the process of creating a membrane protein?
-SRP recognises secretory signal sequence at N terminus, binds to sequence and protein synthesis stops -SRP (attached to sequence) then binds to the SRP receptor on cytosolic face of the ER -SRP is released, protein synthesis restarts -Signal sequence interacts with signal sequence receptor (SSR) within a protein translocator complex (Sec61) results in further synthesis -Signal sequence cleaved by signal peptidase -Reaches stop transfer signal (hydrophobic sequence that spans the bilayer) -C terminus in the cytoplasm and the N terminus in the lumen
What type of receptors do cells that require cholesterol display? What do they recognise?
Cell surface LDL-receptors that recognise specifically Apoprotein B
What is the main advantage of having a large calcium gradient between intracellular and extracellular space?
Changes in intracellular [Ca2+] occur rapidly with little movement
Membrane spanning domains are usually between how many amino acids in length?
18 and 22
What are the approximate intra and extracellular concentrations of chlorine?
Intracellular - 3mM Extracellular - 114mM
How can peripheral membrane proteins be removed from the lipid bilayer?
Changes in pH or ionic strength
How many of the following modes of mobility are permitted for a membrane lipid molecule?
4
What should be used if the half life is long and a rapid effect desired?
Loading dose
How do unsaturated double bonds in fatty acid side chains result in increased membrane fluidity?
Disrupt hexagonal packing of phospholipids
Suggest some examples of calcium sensitive processes in the body/
-Fertilisation -Secretion -Neurotransmission -Metabolism -Contraction -Apoptosis -Necrosis
How could you give a drug to avoid first pass metabolism?
-Parenteral -Rectal -Sublingual
Where are steroid hormone receptors located?
Nucleus
Where are mitochondrial membrane proteins synthesised?
Cytoplasm
Suggest some of the effects that receptors which stimulate adenlyl cyclase can have?
-Increased Glycogenolysis in the liver -Increased gluconeogenesis in the liver -Increased lipolysis in adipose tissue -Relaxation of a variety of types of smooth muscle -Positive inotropic effect in the heart -Positive chronotropic effect in the heart.
What is a receptor?
A molecule that recognises specifically a second molecule (ligand), or family of molecules and in response to binding brings about the regulation of a cellular process.
What is a ligand?
Any molecule that binds specifically to a receptor site.
What are the three restraints on mobility of proteins in the lipid bilayer?
-Lipid-mediated effects i.e. proteins go where cholesterol isn’t -Membrane protein associations -Association with extra-membranous proteins (peripheral proteins)
What is acid extrusion mediated by in most cells?
Na+-H+-exchange (NHE)
Describe the uptake of occupied insulin receptors.
-Insulin binding induces a conformational change in the receptor that allows it to be recognised by the pit -The endosome, insulin and the receptor are bound when it goes to the lysosome N.B. , insulin receptors only congregate over clathrin coated pits when their agonist is bound
What is hereditary elliptocytosis?
Hereditary condition where the spectrin molecule is unable to form stable heterotetramers - resulting in fragile elliptoid cells
Suggest two receptors that are largely recycled after receptor-mediated endocytosis
-Low density lipoprotein (LDL) receptor -Transferrin receptor
Suggest four “non-classical” ligand-gated ion channels
-ATP-sensitive K+ channel -Inositol 1,4,5-trisphosphate (IP3) receptor -P2x-purinoceptor (ATP) -Ryanodine receptor (RyR)
Describe signal transduction for the receptor tyrosine kinase. (starting from agonist binding)
-Agonist binds -Tyrosine Kinase Linked Receptors autophosphorylate upon ligand binding -Phosphorylated receptor tyrosine residues are recognised either by transducing protein or directly by enzymes containing phosphotyrosine recognition sites (SH2 domains) -On association effector enzymes begin a cascade -Transduction of signal into chemical event
What is the effect of the attachment of integral membrane proteins to the cytoskeleton?
Restriction of the membrane proteins lateral mobility
Give the range of values for cellular resting membrane potentials.
Nerve Cells -50 to -75 mV Smooth Muscle Cells around -50 mV Cardiac/skeletal muscle cells have the largest resting potentials of -80 to -90mV
What are partial agonists?
Drugs that cannot produce a maximal effect, even with full receptor occupancy.
What are excitatory postsynaptic potentials are responsible for?
Small depolarisation that triggers voltage-sensitive ion channels to fire a full action potential
What is hyperpolarisation?
Cell interior becomes more negative (opening Cl- or K+ channels)
What are prodrugs?
Inactive drug that when given is activated by the liver.
Suggest two receptors that are largely targeted for destruction by lysosomes after receptor-mediated endocytosis
-Epidermal growth factor (EGF) receptor -Insulin receptors
What molecule holds the ribosomes to the endoplasmic reticulum during synthesis of membrane proteins?
Ribophoryns
What is the structure of classical ligand-gated ion channel receptor?
-Receptors are composed of five homologous, non-identical pp. subunits -The ion-conducting pore is made up of the M2 transmembrane segment from each of the receptor subunits -Agonist binding occurs in the extracellular N-terminal domain of subunits containing a binding site
What is the equilibrium potential of an ion?
The membrane potential at which the electrical and diffusional forces balance one another and there is no net movement of the ion.
What is hereditary spherocytosis? What does condition does it result in?
A hereditary condition where the amount of spectrin production is heavily reduced which results in haemolytic anaemia
What is the local circuit theory of propagation?
The depolarisation of a small region of membrane produces transmembrane currents in neighboring regions. As Na+ channels are voltage gated, this opens more channels, causing the propagation of the action potential.
How might tyrosine kinase-linked receptors initiate a Ca2+ signal?
Activation of phospholipase C gamma and inositol 1,4,5-trisphosphate
What are the two types of glycolipid? What is the distinction between the two?
-Cerebrosides - The head group is a sugar monosaccharide -Gangliosides - The head group is an oligosaccharide
How might a resting membrane potential be found?
With use of a microelectrode, filled with a conducting solution, which penetrates the cell membrane.
Identify three things that may lead to disease through adventitious uptake into cells by receptor-mediated endocytosis
-Cholera toxin -Diptheria toxin -Membrane-enveloped viruses
How does an integral ion channel function?
Agonist binding to ligand-gated ion channels results in a conformational change and the opening of a gated channel. The channel then permits the flow of ions down an electrochemical gradient.
Which protein is most important in allowing ionic movement to establish resting membrane potential?
Voltage-insensitive K+ channels
In depolarised cardiac sarcolemma what happen to Na+-Ca2+-exchange activity?
Reverses to transport Ca2+ into the cell
What does acetylcholine binding to M2 muscarinic receptors lead to? What is the effect?
Inhibits adenylyl cyclase and stimulates K+ channels. This then slows the cardiac pacemaker cells.
What are the two most common carbon atom chain lengths that are present in fatty acid chains in naturally occuring phospholipid molecules?
C16 and C18
Why does opening K+ channels result in a negative chronotropic effect?
Increase plasma membrane permeability to K+ causes hyperpolarisation, slowing the intrinsic firing rate, resulting in a negative chronotropic effect.
What is pinocytosis?
The invagination of the plasma membrane to form a lipid vesicle. This permits the uptake of impermeable extracellular solutes and retrieval of plasma membrane.
Excitatory postsynaptic potentials (EPSPs) may be elicted by opening channels for which two ions?
-Na+ -Ca2+
What are the 4 methods of signal transduction via receptors?
-Membrane bound receptors with ion channels -Membrane bound receptor with integral enzyme activity -Membrane bound receptors which couple to effectors by transducing proteins (most common) -Intracellular receptors
In general terms how does a membrane bound receptor with transducing proteins (G-Protein Coupled Receptor) work?
Seven transmembrane domain receptors (7TMDR) couple to effector molecules (ion channels/enzymes). This is done via a transducing molecule, which is a GTP-binding regulatory protein (G-Protein).
Why is there a delay before local anaesthetics work?
They act on open channels - have to wait for an action potential to actually start
What are the three types of antagonist?
-Reversible Competitive Antagonism -Irreversible Competitive Antagonism -Non-Competitive Antagonism
During repeated drug administration after how many half lives is the new steady state achieved?
5 half lives
Why can the asymmetry of protein orientation be very important?
Orientation of proteins in biological membranes is important for their function, e.g. receptors must face into the extracellular space to function properly.
How can morphine act to inhibit the release neurotransmitter?
-Morphine stimulates pre-synaptic μ-opiod receptors -This leads to a G protein effect -The βγ subunit heterotrimer interact with VOCCs to reduce Ca2+ entry, thus reducing neurotransmitter release
What is the most common drug used to treat atrial fibrillation? What is its half life?
Digoxin - 36 hour half life
What is the function of PMCA?
An high affinity, low capacity antiport that uses ATP to expel Ca2+ from the cell in exchange for H+
Briefly describe the mechanism of action of a G protein.
-An activated receptor interacts with the the G protein complex -The bound GDP switches to GTP on the alpha subunit -The affinity the sub units have for the receptor and each other decreases and they are released and act as effectors
Describe the process of phagocytosis.
-Binding of a particle to receptors on the plasma membrane, the cell extends pseudopods that permit further interactions -Membrane invagination/particle internalisation via a ‘membrane zippering’ mechanism -Internalised phagosomes fuse with lysosomes to form phagolysosomes in which the particulate material is degraded
Suggest three receptors that interact directly with DNA.
-Cortisol receptor -Oestrogen receptor -Thyroid hormone receptor
What is the function of NCX?
A low affinity, high capacity antiport that expels 1x Ca2+ from the cell in exchange for 3x Na+ using the concentration gradient set up Na+/K+-ATPase
What is slow synaptic transmission?
The receptor protein and ion channel are separate proteins, they may be linked by either G-Proteins or intracellular messengers.
What is capacitance?
The ability to store charge. Therefore, a membrane with a high capacitance will take more current to charge
How are coated vesicles uncoated?
Uncoated in an ATP-dependent process by uncoating proteins
What are the two types of fast synaptic transmission?
-Depolarising transmitters lead to a change in membrane potential known as excitatory postsynaptic potential (EPSP) -Hyperpolarising transmitters lead to a change in membrane potential known as inhibitory postsynaptic potential (IPSP)
What is the main specialised function of the mitochondrial membrane?
Energy conservation by oxidative phosphorylation
What happens during the upstroke (depolarisation) of an action potential?
The Na+ channels open, the Na+ floods into the cell and this leads to depolarisation.
What mode of mobility is least likely to occur to a lipid bilayer? Why?
Flip-flop motion due to the high energy requirement
What is the IC50?
Concentration of antagonist giving 50% inhibition.
Which two key molecules are found as integral proteins on the erythrocyte cytoskeleton?
-Band 3 - anion exchanger -Glycophorin A
What are the two types of pinocytosis?
-Fluid-phase -Receptor mediated endocytosis
In myelinated nerve fibres where are the Na+ and K+ located.
Na+ channels are located in the nodes of Ranvier, while K+ channels may be more widely distributed
Where may the energy for active transport come from?
-Hydrolysis of ATP -The concentration gradient of the transported substance and/or the electrical potential across the membrane
Which protein creates disulphide bonds in membrane proteins? Where does it do this?
Disulphide isomerase in the endoplasmic reticulum
What do we mean when we describe G proteins as heterotrimeric?
They are made up of three distinct subunits, α, β, and γ.
Why do nerve fibres with a greater diameter have a faster conduction velocity?
The reduced resistance to local current flow as a result of the relative abundance of ionic species in the axoplasm
What is transcytosis?
Some ligands that remain bound to their receptors may be transported across the cell
What are spare receptors?
Some tissues have more receptors than required to produce a maximum response. i.e. EC50 < Kd (50% of the maximal response takes less than 50% receptor occupancy)
How does myelination increase conduction velocity?
-Reduces Capacitance -Increases Membrane Resistance
How does ion transport result in regulation of cell volume?
Water follows osmotically active ions, if there is a lot of osmotically active ions moving in the cell swells.
What type of G protein do β1 receptors stimulate? What does this stimulate or inhibit?
Gs - stimulates adenlyl cyclase
In cardiac muscle how do calcium antagonists exert their anti-dysrhythmic action?
Blocking the voltage-sensitive Ca2+ channel
Which membrane-bound enzyme has integral guanylyl cyclase activity?
Atrial natriuretic peptide (ANP) receptor
What is the difference between Devic’s disease and MS?
Multiple sclerosis is the breakdown of the myelin sheath around all CNS nerves. Whereas, Devic’s disease is the breakdown of the myelin sheath around the optic and spinal nerves only.
What are VOCC channels?
Channels that open to allow the influx of calcium down its concentration gradient, triggered by membrane depolarisation
What channel mediates excitation-contraction coupling in skeletal muscle?
Voltage-sensitive Ca2+ channels
The activation of which receptors leads to increased calcium release and therefore smooth muscle contraction?
-a1 adrenoreceptor -M3 receptors
What percentage of a membrane is water when hydrated?
20%
What is the approximate extracellular Ca2+ ion concentration?
2 millimolar
Transmembrane movement of which ion predominates in the establishment of the resting membrane potential? Which ways does it move?
K+ moving outwards
Give some examples of transmitters released at excitatory synapses.
Acetylcholine, Glutamate
What happens to the resting membrane potential in hyperkalaemia? (raised serum potassium) How does this affect action potentials?
Becomes more positive. The membrane potential is closer to the threshold for firing of an action potential
What drug can be used to alter the deformability of the erythrocyte?
Cytochalasian drugs
What type of G protein do M2 receptors stimulate? What does this stimulate or inhibit?
Gi - inhibits adenlyl cyclase
What happens during the downstroke (repolarisation) of an action potential?
-The sodium channels are inactivated leading to the Na+ influx stopping -The K+ channel open and the K+ flows out
What types of molecules can pass through membranes?
-Small, uncharged polar molecules -Hydrophobic molecules
Where does final processing of carbohydrate modifications of newly synthesised membrane proteins occur?
Trans-golgi
What are dihydropyridines?
DHPs are specific blockers of L-type Ca2+ channels
What two structures can an amphipathic molecule form in water?
-Micelle -Bilayer
When are drug interactions in metabolism likely to be clinically significant?
-Drugs with low therapeutic ratios -Drugs being used at the minimum effective concentration (oral contraceptive) -Drugs with zero order kinetics
How does the pharmacological agent tetrodotoxin (TTX) work?
It binds to fast voltage-gated sodium channel blocking them and therefore preventing an action potential from being fired
What two channels can alkali influx be mediated by?
- Na+-Cl–HCO3–H+-co-transport -Na+-HCO3-co-transport
What confirmation are double bonds that occur in naturally occuring phospholipids in?
Cis
What is the only phospholipid not based on glycerol? Where is it usually found?
Sphingomylein found in myelin for signal transduction
What is the oral bioavailability of the drug?
Proportion of the drug given orally (or any other route except IV) that reaches the circulation unchanged
During membrane depolarisation which channels begin to open?
Voltage-sensitive Na+ and K+ channels begin to open at the same time. N.B. no change in the number of voltage-insensitive K+ channels that are open
What is the Na+/K+-ATPase? What is its function?
A plasma membrane associated pump (anti port) that uses energy from ATP hydrolysis to move 2K+ into the cell and 3Na+ out of the cell. -Forms Na+ and K+ gradients (necessary for electrical excitability) -Drives Secondary Active Transport (Control of pH, regulation of cell volume and Ca2+ concentration and absoprtion of Na+ in epithelia)
Which five key molecules are found as peripheral proteins on the erythrocyte cytoskeleton?
-Spectrin -Actin -Adducin -Band 4.1 -Ankrin (band 4.9)
How would you work out the therapeutic ratio?
The maximum lethal dose divided by the minimum effective dose. LD50/ED50
What is the function of the Beta sub unit of Na+/K+-ATPase?
The glycoprotein directs pump to the surface
How do irreversible competitive antagonists prevent a maximal response at higher concentrations?
Spare receptors are filled by the antagonist, not leaving enough receptors free to illicit a maximal response.
What is adenlyl cyclase?
Adenylyl Cyclase is an integral plasma membrane protein that can be either activated (via Gs) or inhibited via (Gi) by activation of different receptors
What is alkali extrusion mediated by?
Anion-exchanger in most cells
What can amino acid efflux cause?
Cell shrinking
Explain how the influx of calcium at a motor nerve terminal leads to ACh being exocytosed?
-Ca2+ enter through Ca2+ channels -Ca2+ binds to synaptotagmin -Vesicle containing ACh brought close to membrane -Snare complex forms a fusion pore -Transmitter released through this pore
How does the pharmacological agent succinylcholine work?
It is a depolarising blocker of nicotinic ACh receptors. It binds and as soon as the channels open and then close they become desensitised - a constant depolarisation which means no APs due to accommodation.
Inhibitory postsynaptic potentials (PSPs) may be elicted by opening channels for which two ions?
-K+ -Cl-
Identify three ligands that end up in the lysosomal fraction after receptor-mediated endocytosis
-Epidermal growth factor (EGF) -Insulin -Low density lipoprotein (LDL)
Why is the erythrocyte cytoskeleton important?
Helps maintain the deformability necessary to move through capillary beds
What is the velocity of myelinated axons proportional to?
Diameter
How do receptor operated calcium channels work?
A ligand/agonist binds to the channel, opening it and allowing Ca2+ to enter down its concentration gradient.
How is the action of a G protein terminated?
The alpha subunit eventually works as a GTPase, hydrolysing the GTP with this then increases the attraction between the subunits, rejoining the heterotrimeric molecule.
What happens to the transporter in diarrhoea?
CFTR is overly active once phosphorylated by Protein Kinase A. This leads to Cl- being excessively transported into the lumen.
Describe how an intracellular receptor causes an effect.
-Hydrophobic ligands (like cortisol, oestrogen and T3/4) pass through plasma membrane -Ligands bind to intracellular receptors -Activated receptor translocates to the nucleus, where it binds to control regions -Regulates gene expression N.B. a hell of a lot slower than extracellular
Suggest four membrane-bound receptors with integral enzyme activity
-Atrial natriuretic peptide (ANP) receptor -Epidermal growth factor (EGF) receptor -Insulin receptor -Platelet-derived growth factor (PDGF) receptor
What is the difference between schwann cells and oligodendrocytes?
Schwann cells myelinate peripheral axons, whereas, oligodendrocytes myelinate axons in the central nervous system
Define the term agonist.
Any molecule that binds specifically to a receptor site and produces the activation of a receptor.
What type of G protein do α2 receptors stimulate? What does this stimulate or inhibit?
Gi - inhibits adenlyl cyclase
What properties of an axon lead to a high conduction velocity?
-A High Membrane Resistance -A High Axon Diameter -A Low Membrane Capacitance
What type of G protein do α1 receptors stimulate? What does this stimulate or inhibit?
Gq - stimulates PLC
What is an acceptor?
If a molecule operates in the absence of it’s ligand, it is not a receptor, it is an acceptor
How would you work out drug bioavailability?
(Area under the curve orally/Area under the curve injected) x 100
Which drugs have only affinity?
Antagonists
The glycine receptor ion channel is permeable to which ions?
Cl-
Which protein connects the spectrin protein section of the cytoskeleton with the Band 3 protein?
Ankyrin
How can a reversible competitive antagonist be overcome?
Can be overcome by high concentrations of agonists, thus cause a parallel shift to the right of the agonist concentration-response curve.
What type of G protein do M3 receptors stimulate? What does this stimulate or inhibit?
Gq - stimulates PLC
Suggest three possible members of the “classical” ligand-gated ion channel receptor family
-Gamma aminobutyric acid (GABA) receptor type A (GABAAR) -Glycine receptor -Nicotinic acetylcholine receptor (nAChR)
Using opioids as an example, what is the clinical significance of using partial agonists?
Opioids are used for pain relief, however, they can cause respiratory depression and therefore death. Morphine is a full agonist, however, buprenorphine is a partial agonist, with a higher affinity but lower efficacy than morphine. Therefore it binds better but there is less risk of death.
What are the four permitted modes of mobility of lipids in a lipid bilayer?
-Intra-chain motion -Fast axial rotation (rotational) -Fast lateral diffusion (within plane of bilayer) -Flip-flop motion
Describe the process that occurs when an LDL molecule binds to its receptor.
-Clarithin pit invaginates to form a coated vesicle -Vesicles uncoated by ATP and fuse with endosomes (CURLs) (which are big vesicles) -The endosome (CURL) has a low pH which causes the LDL to dissociate -LDL receptor is recycled and the endosome fuses with lysosomes to get the cholesterol from the esters and is released into the cell
What is significant about pure lipid bilayers?
Highly impermeable to ions and most polar molecules, allowing only small, uncharged molecules to pass through.
How is calcium removed from a mitochondria?
Ca2+ uniporter
What does Kd indicate?
Dissociation constant - affinity as it is the concentration needed for 50% occupancy. A lower Kd value relates to a higher affinity.
In cells where acid extrusion isn’t mediated by Na+-H+-exchange (NHE) what is it mediated by?
Na+-Cl–HCO3–H+-co-transport
What does the association of clathrin with coated-pits drive?
Drives the internalisation of coated vesicles
What is fast synaptic transmission?
In fast synaptic transmission, the receptor protein is also an ion channel. The binding of transmitter causes the channel to open.
When are protein binding interactions significant?
-Highly bound to albumin (90%+) -Small volume of distribution -Low therapeutic ratio
During the reaction cycle where is the Na+ pump phosphorylated?
One of its aspartate residues
What are the 5 main functions of biological membranes?
-Continuous, selective permeability barrier -Control of enclosed chemical environment -Control information flow between cells and the environment (Communication) -Recognition i.e signalling, adhesion -Signal generation i.e. chemical/electrical
How may slow neurotransmission be mediated?
G-protein-coupled receptors and signalling to ion channels by the activation of intracellular signalling pathways
How do G-Protein Coupled Receptors (GPCRs) release calcium from the sarco/endoplasmic reticulum?
-A ligand binds to the GPCR on the cell membrane, activating its Gαq subunit -This subunit then binds to the membrane phospholipid PIP2, releasing IP3 -IP3 binds to its receptor on the sarcoendoplasmic reticulum, triggering the release of calcium down its concentration gradient into the cell.
What is the function of NBC?
Uses the Na+ concentration gradient set up by Na+/K+-ATPase to push out acid and moves base in which raises intracellular pH and regulates cell volume
What are the approximate intra and extracellular concentrations of sodium?
Intracellular - 10mM Extracellular - 145mM
What are the two types of channel gating? How do they work?
-Ligand gating where it can be opened or closed by binding of a ligand by a transmitter (extracellular/intracellular) -Voltage gating where the channel opens or closes in response to changes in membrane potential
Which transporters control the resting calcium levels?
-PMCA - Plasma membrane Ca2+-ATPase -SERCA - Sarco(endo)plasmic Reticulum Ca2+-ATPase -NCX - Na+/Ca+-exchanger -Mitochondrial Ca2+ uniports
In what order do local anaesthetics block axons?
- small myelinated axons 2. un-myelinated axons 3. large myelinated axons
How does IP3 act?
Interacts with specific intracellular receptors on the endoplasmic reticulum (ER) to allow Ca2+ to leave the lumen of the ER and enter the cytoplasm.
What is the main disadvantage of having a large calcium gradient between intracellular and extracellular space?
Ca2+ overload leads to loss of regulation and cell death
Describe how noradrenaline can lead to arteriolar vasoconstriction
-Noradrenaline acts on α1-adrenoceptors to stimulate phospholipase C and IP3 production via Gq. -IP3 releases ER Ca2+ and initiates a contractile response
Suggest 4 possible head groups on phospholipid molecules.
-Choline -Amines -Amino acids -Sugars
What is the energy for passive transport provided by?
the concentration gradient of the transported substance and/or the electrical potential across the membrane
What occurs when a Class I drug is given at the same time as a Class II drug?
Class II displaces class I on albumin
What is the function of NHE?
Na+/H+ Exchanger uses the Na+ concentration gradient set up by Na+/K+-ATPase to take in Na+ and push out H+. This raises the intracellular pH making it less acidic which regulates cell volume and activates growth factors.
How is Ca2+ induced Ca2+ release (CICR) used to release calcium from the sarco/endoplasmic reticulum?
Ca2+ binds to the Ryanodine receptor on the side of the Sarco/endoplasmic reticulum, triggering the release of calcium down its concentration gradient into the cell.
Increased transmembrane flux of which two ions may result in membrane depolarisation?
-Na+ -Ca2+
Define the term affinity in relation to pharmacology.
Likelihood of a ligand binding to its target
What is Emax?
The maximum response possible
How does a membrane bound receptor with integral enzyme activity work?
Agonist binding to the extracellular bit of these receptors causes a conformational change. This activates an intrinsic enzyme activity, contained within the protein structure of the receptor.
What type of G protein do β2 receptors stimulate? What does this stimulate or inhibit?
Gs - stimulates adenlyl cyclase
What is the role of Gq proteins?
Interact with the membrane bound enzyme phospholipid phosphatidylinositol 4,5-bisphosphonate (PIP2) to generate the second messengers inositol 1,4,5-trisphosphate (InsP3) and diacylglycerol (DAG)
Suggest five mechanisms that may be responsible for raising intracellular free Ca2+ ion concentration
-Inositol 1,4,5-trisphosphate (IP3) receptors -Ryanodine receptors -Voltage-sensitive Ca2+ channels -Na+-Ca2+-exchange -Ligand gated Ca2+ channels
What is the consequence for the membrane potential of an increase in membrane permeability to Na+ ions?
Depolarisation
Increased transmembrane flux of which two ions may result in the membrane hyperpolarisation?
-K+ -Cl-
What type of ion channels accompanies the nicotinic ACh receptor?
Classical ligand-gated ion channel
What is the problem with NCX in ischaemia?
In ischaemia the ATP is depleted and therefore the sodium pump is inhibited leading to high intracellular sodium. NCX reverses and starts pushing sodium out and taking in a shitload of calcium…oh no!
What is the velocity of unmyelinated axons proportional to?
The square root of the diameter
Why does accommodation occur?
Accommodation occurs because the progressive depolarisation gives time for some Na+ channels to inactivate and for some K+ channels to open
