M+R Flashcards
What is a plasmalogen and give an example?
A non classical phospholipid
Sphingomyelin - doesn’t have a glycerol
What makes up a cell membrane including percentages?
Dry weight
Lipid 40%
Protein 60%
Carbohydrate 1-10%
Water 20%
What are the two main types of glycolipid and what is the difference between them?
Cerebroside - head group is a monomer
Ganglioside - head group is an oligosaccharide
What are the possible lipid motions?
Flexion
Lateral diffusion/drift
Rotation
Flip flop
What are the possible protein movements?
Rotation
Lateral diffusion/drift
Conformational change
Why can’t proteins “flip flop”?
It requires too much energy
What is the evidence for membrane proteins?
Freeze fracture
Specificity of function
SD page
What determines what movement proteins are capable of?
Size
Association with extra-membranous proteins
Move toward fluid areas and cholesterol poor areas
What are the differences between integral and peripheral membrane proteins?
Peripheral - bound to surface by electrostatic and hydrogen bonds. Removed by change in pH or ionic strength
Integral - strongly bound to hydrophobic areas. Removed by detergents or organic solvents
Outline the protein secretion pathway
A free ribosome initiates protein synthesis from mRNA molecule. A signal sequence is produced at the N-terminal. SRP binds to the signal sequence and stops protein synthesis. Ribosome goes to ER due to GTP on SRP. SRP dissociates and protein synthesis restarts with the polypeptide feeding into the ER via a pore. Signal sequence removed and ribosome dissociates
How does a membrane protein remain in the membrane? How can you get proteins with multiple trans membranous regions?
A stop transfer signal is in the polypeptide and this stops the protein feeding into the pore.
Multiple start and stop transfer sequences
What does cholesterol do in a membrane?
Increases stability by increasing fluidity when it is cold by pushing phospholipids apart and decreasing fluidity when it is too hot by forming hydrogen bonds
Why is the membrane referred to as a fluid mosaic?
Fluid - integral components move around
Mosaic - many different components
What makes up an erythrocytes cytoskeleton?
Spectrin and actin molecules attached to the membrane by adaptor proteins - ankyrin and glycophorin - which attach to band 3 and 4.1 respectively
What types of molecule can pass through the cell membrane? And therefore cannot?
Hydrophobic
Small, uncharged, polar molecules
Large, uncharged, polar molecules
Ions
What are the differences between passive diffusion, facilitated diffusion and active transport?
Passive - dependent on permeability and gradients
Facilitated - membrane permeability increased by incorporation of a protein
Active transport - uses energy from ATP hydrolysis to move molecules against an unfavourable gradient
What are the 3 types of transporter?
Uniport
Symport
Antiport
Name two proteins that move K+ ions and explain how
Na pump - 3Na+ out 2K+ in using ATP
K+ channels - K+ diffuses out
Name 4 proteins that move calcium and explain how
Ca2+ATPase - use ATP to pump Ca2+ out
PMCA - H+ in and Ca2+ out. Uses ATP. High affinity, low capacity
SERCA - move Ca2+ into the SR/ER for H+ using ATP. High affinity, low capacity
NCX - move Ca2+ out and 3Na+ in. Low affinity, high capacity
What happens to NCX in the case of ischaemia?
Less ATP produced so Na+ can’t be pumped out and accumulates in the cell, depolarising it and reversing the direction. Ca2+ accumulate inside and causes cell death
Name two proteins that affect pH and explain how
NHE - 1Na+ in, 1H+ out using Na+ gradient. Raises pH
AE - Cl- in HCO3- out. Lowers pH
How is cell volume controlled?
If cell is swelling - move K+ and Cl- out and water will follow out
If cell is shrinking - move Na+ and Ca2+ in and water will follow inside
Explain how renal anti hypertensive therapy works
Reduce renal Na+ reuptake which reduces the reuptake of other molecules and therefore reduce how much water is reabsorbed by osmosis. His lowers blood volume and therefore blood pressure
What does aquaporin do and how is it placed in a membrane?
Increase membrane permeability to water. Anti diuretic hormone increases its inclusion in the membrane
What do loop diuretics do and give specific examples
Block Na+ in thick ascending limb.
Amiloride prevents Na+ reuptake.
Aldosterone would increase reuptake so spironolactone is used to counter the aldosterone
How can a CFTR molecule cause diarrhoea?
It becomes overly active if it is phosphorylated by protein kinase A. This means excess Cl- moves into the lumen and water will follow
How can a faulty CFTR gene cause cystic fibrosis?
Doesn’t work so Cl- accumulates in cell and water follows in. This means the mucus has less water so is very thick
Define the resting membrane potential
The potential inside the cell relative to the extra cellular solution
Give the approximate membrane potential ranges of:
Nerve cells
Smooth muscle cells
Cardiac and skeletal muscle cells
-50 to -75
Approximately -50
-80 to -90
How is the resting membrane potential established?
Predominantly from the open K+ channels
What is the equilibrium potential and how can it be calculated?
The membrane potential at which there is no next movement of the ion across the membrane. Calculated using the Nernst equation
Define depolarisation and what ions movements can cause it?
Membrane potential decreases in size (gets less negative)
Na+ or Ca2+ ions
Define hyperpolarisation and what ions would move to cause it?
Membrane potential increases in size (becomes more negative)
Cl- or K+ ions
What is the difference between fast and slow synaptic transmission?
Fast - the receptor protein is also the ion channel
Slow - the receptor is coupled to the ion channel e.g. by G proteins
What channels would open in excitatory synapses and what are the neurotransmitters?
Na+ and Ca2+ channels
Glutamate and acetylcholine
What channels would open in inhibitory synapses and what are the neurotransmitters?
K+ or Cl- channels
Glycine or GABA
What is an action potential? What are some features of it?
A change in the voltage across a membrane. Dependent on ionic gradients and relative permeability of the membrane. All or nothing response. Propagated without loss of amplitude
What is the sodium hypothesis?
The cell is depolarised to the threshold potential and voltage gated Na+ channels open allowing Na+ influx due to the concentration gradient. This causes further depolarisation and the opening of more channels
How does repolarisation occur?
During prolonged depolarisation the Na+ channels start to close by inactivation and K+ channels open causing the Na+ influx to stop and K+ effluent to start.
Why is an action potential an all or nothing response?
Because positive feedback will open enough Na+ to send an impulse but has to be reached in the first place
What are the refractory periods?
Absolute refractory period - nearly all Na+ channels are inactivated so excitability is 0
Relative refractory period - some Na+ channels are recovering so excitability slowly returns to normal
Explain accommodation
A slower stimulus will require a larger depolarisation to reach the threshold potential as Na+ channels are becoming inactivated
What is the structure of a voltage gated Na+ and Ca2+ channel?
1 peptide 4 homologous repeats 6 transmembrane domains 1 voltage sensitive domain Functionality requires 1 subunit
What is the structure of a voltage gated K+ channel?
4 peptides
6 transmembrane domains
1 domain = voltage sensitive
Functionality requires 4 subunits
How might an anaesthetic like procaine work?
By blocking Na+ channels stopping action potential generation
What is the order that anaesthetics block Na+ channels and what is the significance of this?
Small myelinated
Non myelinated
Large myelinated
Sensory neurones are affected before motor neurones
How could you measure conduction velocity?
Electrode raises membrane potential to threshold generating an action potential. Then measure the change in potential between stimulating cathode and recording anode. Calculate velocity by distance/time
What is local circuit theory?
Depolarising a small region produces transmembrane currents in neighbouring regions which open their Na+ channels, propagating the action potential. The larger the local current, the faster the transmission