M&R Flashcards
What is the concentration of Na in ICF and ECF?
- ICF = 10mM
- ECF = 145mM
What is the concentration of K in ICF and ECF?
- ICF = 155mM
- ECF = 4mM
What is the concentration of Ca in ICF and ECF?
- ICF = 100nM (1 x 10-7)
- ECF = 1.5mM (1 x 10-3)
What movements can lipid molecules make in lipid bilayer? How does this differ with proteins?
- Intra-chain motion
- Rotation
- Lateral diffusion
- Flip-flop
Proteins are unable to flip-flop due to large hydrophobic moieties
Briefly describe secretory protein synthesis
- Free ribosome initiates synthesis from mRNA
- Signal sequence binds to signal recognition particle (SPR)
- GTP binds
- Directs ribosome to SRP receptor on membrane
- SRP dissociates and synthesis continues
- Signal sequence removed by signal peptidase
How does secretory protein synthesis differ for proteins embedded within membrane?
- Synthesis continues as normal but there is inclusion of stop transfer signal
- Stop transfer signal is highly hydrophobic and remains within membrane
- Signal peptidase cleaves signal sequence
- Some proteins contain many stop transfer signals and so have many transmembrane portions
Why is the erythrocyte cytoskeleton important? Give a disease that causes this
Without it RBCs become more sherical and are lysed by shearing forces in capillary bed
Hereditary spherocytosis - depletion of spectrin levels = haemolytic anaemia
Which substances can pass through the phospholipid bilayer?
Hydrophobic molecules and small uncharged polar molecules
- O2
- CO2
- N2
- Benzene
- H2O
- Urea
- Glycerol
Describe channels controlling resting intracellular Ca2+
- PMCA = plasma membrane Ca2+-ATPase
- High affinity, low capacity
- SERCA = Sarco(endo)plasmic reticulum Ca2+-ATPase
- High affinity, low capacity
- NCX = Na+-Ca2+-exchanger
- Low affinity, high capacity
What is an action potential? What does is depend on?
A change in voltage across a membrane
Depends on ionic gradients and relative permeability of membrane
What is the equlibrium potential for an ion?
Membrane potential at which there is no net movement of ion across membrane
Conc gradient = electrical gradient
Can use Nerst equation to calculate
What affects conduction velocity?
- Membrane resistance - high membrane resistance = high potential difference = more voltage gated Na channels = increases conduction velocity
- Axon diameter
- Membrane capacitance
Which cells form myelin?
- Schwann cells - peripheral axons
- Oligodendrocytes - CNS
Define affinity
The ability of a drug to bind to a specific receptor
Define efficacy
The maximal effect of a drug when bound to a receptor - how well does it produce a response
Expressed in terms of %
Describe how calcium causes neurotransmitter release
- Calcium influx through voltage gated channels
- Calcium binds to synaptotagmin which leads to formation of snare complex with vesicle bound
- Fusion pore is then made from snare complex and neurotransmitter is released into synaptic cleft
How is calcium handled in the cardiac myocyte?
- Following depolarisation there is calcium entry through voltage operated calcium channels
- Bind to ryanodine receptors on SR
- Causing explosive release of large amounts of calcium from intracellular stores
- This is calcium induced calcium release
Apart from calcium induced calcium release how else is calcium released from intracellular stores?
- Ligand binds to G-alpha-q receptor
- This then causes conversion of PIP2 into IP3
- IP3 binds to IP3 receptor in SR membrane, opening channels for calcium to move down it’s concentration gradient
What type of receptor is an insulin receptor?
- Tyrosine kinase linked receptor
- Autophosphorylation on ligand binding
Why can cells become desenstised to high circulating insulin?
- Insulin receptors are degraded when they are taken up into the cell attached to insulin
- This allows for a reduction in the number of insulin receptors on membrane surface
How are immunoglobulins transported across the placenta?
- Transcytosis
- Ligand remains bound to receptors as it is transported across the cell and released on the opposite membrane
Define Bmax and Kd
- Bmax = maximum binding capacity
- Give information on the number of receptors
- Kd = dissociation constant
- Measure of affinity, concentration needed for 50% occupancy
- The lower the Kd the higher the affinity
What are the types of antagonism?
- Reversible competitive antagonism
- Increases EC50, no change on maximal response
- Irreversible competitive antagonism
- Decreases maximal response, EC50 decreases with increasing concentrations of drug
- Non-competitive antagonism
- Decreases maximal response, no change of EC50
