M+R Flashcards
What are the important functions of membrane bilayers
Highly selective, permeable barrier
Control of the cellular environment
Communication
Recognition
What is the rough composition of the membrane bilayer?
40% lipid
60% protein
1-10% carb
What type of bonding allows phospholipids to form bilayers?
VDW forces, hydrophobic interaction, hydrogen bonding
What are the four types of motion possible in a phospholipid bilayer?
Flexion
Rotation
Laterial diffusion
Flip flop
What type of double bond is common in the fatty acids of phospholipids? What effect does this have?
Cis - introduces a kink
Reduces membrane packing, so fluidity is increased
What is the most common head group?
Choline
What is sphingomyelin?
The only phospholipid not derived from glycerol - phosphocholine group can be replaced by a sugar to produce a glycolipid
What is a cerebroside?
A glycolipid with one sugar head monomer
What is a ganglioside?
A glycolipid with multiple sugar head monomers
What is cholesterol’s role within the bilayer?
To maintain the correct fluidity, both:
- forms interactions with hydrophobic fatty acids to decrease fluidity
- reduces phospholipid packing to increase fluidity
What are the functions of membrane proteins?
Relating signals between the internal and external environment of the cell
Transportation of ions/molecules across the membrane
Cellular adhesion
How can peripheral proteins be removed?
Changes in pH or ionic strength
How can integral proteins be removed?
Detergents, or substances which compete for non polar interactions
What is the evidence for membrane proteins?
Functional - facilitated diffusion, ion gradients, specificity of cellular response
biochemical - membrane fractionation and freeze fracture
What motion is possible for membrane proteins?
Conformational change
Rotational
Lateral
What motion is not possible for membrane proteins and why?
Flip flop - not energetically possible and would destroy the membrane and the protein would not function (asymmetry)
Why are proteins more restricted in their mobility?
Size aggregation to other proteins tethering to EC matrix or IC cytoskeleton interactions with other cells lipid mediated effects (cholesterol)
What is protein topology?
The orientation of a protein - essential for proper function
Which proteins involved in the erythrocyte cytoskeleton are integral?
Band 3 and glycophorin A
Which proteins involved in the erythrocyte cytoskeleton are peripheral?
Spectrin Actin Ankyrin Adducin Band 4.1
How does membrane protein synthesis differ from the normal synthesis of a secretory protein?
Presence of a strop transfer signal which releases the membrane protein from the protein translocator into the lipid bilayer, so that synthesis continues in the cytoplasm
What are the two types of haemolytic anaemias?
hereditary spherocytosis is a depletion of spectrin by 40-50% so that the erythrocyte shape is distorted and is lysed
Hereditary elliptocytosis is an ability to form spectrin a2b2 heterotetramers so the erythrocytes are elliptical shaped
What types of molecules can diffuse through the plasma membrane?
Hydrophobic molecules (resp gases) and small uncharged polar molecules (water)
What types of molecules cannot diffuse through the plasma membrane?
Large uncharged polar molecules (glucose)
Ions
What does the rate of diffusion depend upon?
The concentration gradient and the permeability of the barrier
I/O concs of Na+
I = 12mM O= 145mM
I/O concs of K+
I= 155mM
O=4mM
I/O concs of Cl-
I=4mM
O=123mM
I/O concs of Ca2+
I=10-7M
O=1.5mM
Compare the rate of simple and facilitated diffusion
Facilitated is faster - however it is saturable and so produces a hyperbolic curve (conc of substrate v rate)
delta G in passive diffusion
negative
delta G in active diffusion
positive
what is primary active transport?
Energy from hydrolysis of ATP is directly used
what is secondary active transport?
Energy from provided from the movement of a more thermodynamically favourable molecule - in a cotransporter
what is a uniport/symport/antiport
uniport - one species
symport - same direction of two species
antiport - different direction of two species
How is Na+ K+ ATPase activated?
phospohrylation of aspartate residue of alpha subunit
What is the function of the beta subunit?
targeting of the protein
Compare the affinity of PMCA/SERCA/NCX
NCX = lower affinity but higher capacity - main transport of ions
PMCA/SERCA have high affinity but low capacity and so transport residual ions
When can the reversibility of NCX be dangerous?
ischemia > low O2 > low ATP > Na+ K+ pump cannot function > Na+ builds up intracellularly > depolariaztion > NCX reverses > calcium enters
What two transporters are mainly involved in maintenance of pH?
Na+ H+ exchanger
Cl- HCO3- exchanger
How is the control of intracellular pH regulated?
any deviation from the ‘set point’ pH will stimulate activity of the necessary transporter
How is the resting membrane potential maintained?
Na/K+ pump removes Na+ from cell - membrane is impermeable to Na+. K+ builds up in the cell but then diffuses out via a K+ channel
producing a negative membrane potential of -70mV
How is bicarbonate reabsorbed in the proximal tubule?
NaHCO3 in proximal tubule splits into Na+ and HCO3-. Na+ enters the epithelial cell via NHE, and then into the capillary via an Na+K+ pump
HCO3 combines with H+ to form H2O and CO2, and then diffuses into the epithelial cell
The two molecules recombine to produce HCO3- and H+ again. HCO3- enters the capillary via the anion exchanger
How is Na+ absorbed in the cortical collecting duct?
Aquaporins remove any remaining water from the filtrate
Na+ enters the epithelial cell via ENaC, then into the capillary via Na+H+ pump
Spironolactone can be used to reduce water absorption - anti diuretic?
