cell membranes and action potentials Flashcards
what are three forms of gated channels?
Ligand – gated
Voltage – gated
Gap Junctions!
What are the five functions of the cell membranes?
Generate signals in response to electrical & chemical
Facilitate communication between cells & their environment
allow control of the enclosed chemical environment
Form a continuous highly- selective permeability barrier
Allow recognition through presence of signalling molecules, adhesion proteins and allow immune surveillance
what is an action potential?
it is when excitable cells create an electrical signal via the movement of ions across the membrane
what is the membrane referred to if it is both hydrophilic and hydrophobic?
amphiphilic - amphipathic
what makes up a phospholipid membrane?
polar head (phosphate group), fatty acid tail, glycerol
what are the permitted modes of mobility in a lipid bilayer?
flip-flop
flexion
rotation
lateral diffusion
what is an integral protein?
Interact extensively w/ hydrophobic domains of lipid bilayer, can’t be removed by manipulation of pH and ionic strength
what is a peripheral protein?
Bound to surface, Electrostatic and hydrogen bond interactions, Removed by changes in pH or in ionic strength
what are the stages of an action potential?
initial stimulus - trigger of action potential
depolarisation - threshold level (-55 mV) reached, voltage-gated Na+ channels open which results in rapid depolarisation
depolarisation - Na+ inactivated and K+ channels open
hyperpolarisation - overshoot the repolarisation phase due to the movement of K+, until returns to resting membrane
refractory period
period of time in which the cell cannot generate an action potential
salutary conduction
action potential ‘jump’ from node to node
myelin sheaths act as a insulator to conduct APs, name a demyelination disease.
Multiple Sclerosis
what is the neuromuscular junction?
the synapse between a neurone and a skeletal muscle cell
release of a neurotransmitter (aCh)
activates receptors on the post-synaptic membrane (nicotinic receptors)
excitatory synapse
neurotransmitters open ligand gated channels permeable to Na+ and cations (naChR)
usually aCh or glutamate
inhibitory synapse
transmitters open ligand gated channels permeable to K+/Cl-
hyperpolarisation
GABA or glycine
what is the function of Na+/K+ ATPase?
3 Na+ ions out, 2K+ ions in
uses ATP
Myasthenia gravis disease
autoimmune disease where autoantibodies target and destroy nAChRs at the neuromuscular junction
fatigable muscles
what is haemolytic anaemia?
shortened in vivo survival of RBCs and inability of bone marrow to compensate for their reduced life span
Hereditary spherocytosis
spectrin levels depleted by 40-50%
erythrocytes round up
less resistant to lysis, removed by spleen
haemolytic elliptocytosis
defect results from a spectrin molecule
fragile elliptoid cells
Unable to form heterotetramers
intracellular vs extracellular concentrations
Na+ = 10mM in vs 145mM out
K+ = 160mM in vs 4.5mM out
Cl- = 3mM in vs 114mM out
A- = 167mM in vs 40mM out
how are membrane proteins formed?
synthesised in RER bud off in vesicles and fuse to ER membrane
ribosome in the cytosol begins translation from a template molecule of mRNA.
signal recognition particle (SRP) recognises the intrinsic signal sequence in polypeptide brings protein synthesis to a halt temporarily.
SRP-ribosome complex moves to RER at the site of an SRP receptor (docking protein).
SRP dissociates binds to SRP receptor for recycling,
Protein synthesis continues and the polypeptide grows into the ER lumen.
signal sequence on the polypeptide cleaved by a signal peptidase
