introduction to cell membranes 2 Flashcards
red blood cells
-bags of Hb
-simple membrane structure
-biconcave- maximises gas exchange
-change the shape as they travel through arteries and capillaries (squeeze through capillaries and change shape a bit more than arteries)
-sickle cell anaemia: mutation in Hb, causes it to aggregate into long rod like structure, so RBC is prevented from changing shape and forms a sickle cell- bad for oxygen exchange
what do optical tweezers show us
-tensile strength of RBC
what conditions do you get in the cell with different salt levels
-low salt= hypotonic - take in lots of water and eventually burst
-high salt= hypertonic
how is the cytoskeleton linked to the plasma membrane
-several membranes which anchor cytoskeletal mesh
-Mutations in spectrin cause certain types of hemolytic anemia (hereditary elliptocytosis and hereditary spherocytosis)
-unable to change their shape to squeezer through narrow spaces of the capillary
what are key features of biological membranes
-Membranes are asymmetric
-Proteins always have the same orientation in the membrane
-The lipid composition of each of the two halves of the bilayer is different
-sugars found on outside of the cell- or inside of the intracellular compartment
-lots of hydrophobic AA
what determines the blood group of an individual
-the structure of the oligosaccharides attached to sphingomyelin and proteins in the red blood cell membrane and to proteins in plasma and other body fluids
-O is the universal donor
-AB is the universal acceptor
what are the Terminal sugars of the oligosaccharide chains of the blood group substances
-AB won’t reject the blood from any donors because they can accept any of the sugars (O,A or B)
-if you have either A or B antigen then you have the structure of the O antigen but just an addition of one sugar, therefore Onis the universal donor
When is membrane asymmetry important
-COAGULATION (clot formation) – phosphatidylserine on platelets and other cell membranes provides the nucleation site for the coagulation cascade.
-Cell recognition and Clearance- The macrophage plasma membrane contains receptors, which recognise aminophospholipids – phosphatidylserine or phosphatidylethanolamine which are transferred to the outer leaflet of the plasma membrane of apoptotic cells
how do Membranes transport proteins of small molecules
-Active transport
-Electrochemical gradients
-Carriers and channels
what solutes does the phospholipid bilayer act as a barrier for diffusion
-hydrophobic molecules: O2, CO2, N2, benzene (easily pass through)
-small uncharged polar molecules: H2O, urea, glycerol (slight block)
-larger uncharged polar molecules: glucose, sucrose (bit more of a block)
-ion: H+, Na+, HCO3-, K+,Ca2+,Cl-, Mg2+ (almost complete block)
what do Membrane transport proteins do
-Each protein transports a particular solute (sugars, amino acids, nucleotides and ions)
-All are multi-pass (pore like structures) integral membrane proteins
-They allow the solute to pass through the membrane so it does not come into contact with the membranes hydrophobic core
Active versus passive transport
-Passive transport: solute moves down its concentration gradient (channels and carriers).
-Active transport: solute moves against its concentration gradient so requires energy (only carriers).
-The carrier protein is often referred to as a pump, permease or transporter.
whats the transport of solutes is affected by
-electrochemical gradients
-Transport is influenced by membrane potential
-Voltage difference across cells because of excess +ve ions on one side and -ve ions on the other
-Combination of membrane potential and concentration gradient gives an electrochemical gradient
-is the membrane potential is negative inside, then there is a stronger electrochemical gradient for + ve ions
what are electrochemical gradients established by
-Established by ionic concentration differences on either side of the membrane – produced through the action of ion channels and carriers/pumps
-Drive transport processes, convey electric signals in nerves, make ATP in mitochondria, chloroplasts and bacterial membranes.
why do Channels transport solute more rapidly than carriers
-Carrier proteins directly bind to the solute
-Channel proteins only interact very weakly with solute.
-Channel can transport 100 million ions per second (105 faster than any carrier)
how do ion channels work
-Form narrow hydrophillic pores through the membrane
-Are specific for different ions – e.g. potassium channel, sodium channel
-Allow rapid movement of ions down the concentration gradient or electrochemical gradient
-Open and close rapidly
-Regulated by binding of ions, changes in voltage or binding of small molecules (ligands)
-Over 100 different types of channel with different properties
-The target of many toxins and medicines (scorpion venom)
-Mutation in one of these channels, voltage-gated sodium channel SCN9A causes Congenital insensitivity to pain
what happens when Carrier proteins undergo conformational changes to transport solute
-carrier proteins exist in two states
-one can bind strongly worth solute(state A), the other the solute is likely to dissociate (state B)
-solute binds to carrier in state A, carrier undergoes conformational change, solute then dissociates (state B) and moves down its concentration gradient
what can active transport be mediated by
-couple solute with the movement of another solute which moves easily down its concentration gradient
-can use energy to drive ATP pumps
-can harvest the energy of light
what are Three types of carrier-mediated transport
-uniport- simple one solute being ransported- passive transport
-symport- solutes going in the same direction, coupled
-antiport- solutes going in the opposite direction, coupled
how does Carrier-mediated diffusion enhances the rate of transport
-linear relationship between rate of transport and concentration of transported molecule in simple diffusion
-in carrier mediated- initial high rate of uptake, but this high rate is important if solute is in low abundance
what symporters are used in Mammalian plasma membrane
-sodium
what is transport driven by in bacteria, yeast, and intracellular membrane
-hydrogen gradients
whats Transcellular transport of glucose like
-micorvilli face lumen in intestinal cell
-takes glucose up from diet
-high glucose- cells of intestine
-AM there is a sodium glucose symporter where glucose is taken into cell and sodium moves out of cell- drives sodium uptake
-high glucose conc in cell, so glucose diffuses outbox cell through BM through glucose carrier- moves down its conc gradient
-net effect= high conc of sodium in cell therefore NaK pump on BM
what is Glucose uptake is driven by
-electrochemical gradient
-Glucose transport across epithelial cells (such as the enterocytes lining the lumen of the small intestine) involves the combined action of three carriers)
-Glucose/sodium ion symporter at the apical surface
-Sodium/Potassium pump at the basal surface
-Glucose carrier at the basal surface
