Introduction to cell membranes (2) Flashcards
Semester 1 year 1
Why do red blood cells have a biconcave structure?
To increase their surface area for gas exchange
What do optical tweezers show?
Tensile strength of red blood cell membranes
What happens to red blood cells in hypertonic, isotonic and hypotonic solutions?
-hypertonic = water leaves cell + cell becomes crenelated (spiky)
-isotonic = no water moves + cell remains round
-hypotonic = water enters cell + cell eventually bursts
What are red blood cell ghosts?
Predominantly plasma membrane as the haemoglobin is washed away
Why do red blood cells have relatively simple protein compositions?
-they’re terminally differentiated cells
-protein composition is reflective of their function
What do mutations in spectrin cause?
Certain types of haemolytic anaemia
What do integral membrane proteins do?
-anchor cytoskeleton to plasma membrane
-provide structure to the cell
-allow it to change shape
What are key features of biological membranes?
-membranes are asymmetric
-proteins always have the same orientation in the membrane
-lipid composition of each of the 2 halves of the bilayer is different
What is the asymmetry of membranes important for?
-blood groups
-coagulation (clot formation)
-cell recognition + clearance
What blood groups can individuals have?
-O
-A
-B
-AB
What is blood group determined by?
Structure of oligosaccharides attached to sphingomyelin in the red blood cell membrane + to proteins in plasma + other body fluids
Which blood group is the universal donor and which is the universal acceptor?
-O = universal donor
-AB = universal acceptor
What is coagulation?
-clot formation
-phosphatidylserine on platelets + cell membrane provide nucleation site for coagulation
What do macrophage plasma membranes contain and where are they transferred to?
-contain receptors that recognise aminophospholipids
-transferred to outer leaflet of plasma membrane on apoptotic cells
What are liposomes?
Phospholipids form spherical structure in aqueous solution
What is passive transport?
-solutes move down a concentration gradient
-involves channels or carriers
What is active transport?
-solutes move against a concentration so requires energy
-only carriers involved
What can active transport be mediated by?
-coupled carrier
-ATP driven pump
-light driven pump
What produces the ion concentration difference on either side of the membrane that results in an electrochemical gradient?
Produced through action of ion channels + carriers/pumps
Do channels or carriers transport solutes more rapidly and why?
-channels
-carrier proteins directly bind to solute, whereas channels interact very weakly with solute
How does passive transport by a carrier occur?
-solute binds to carrier in state A
-carrier converts into state B
-releases solute on other side of membrae
What are the types of ion channel?
-voltage gated
-ligand gated with extracellular ligand
-ligand gated with intracellular ligand
-mechanically gated
What are the types of carrier-mediated transport?
-uniport
-symport - cotransported ion on same side of transported mol.
-antiport - cotransported ion on opposite side of transported mol.
What is the difference in what drives transport across mammalian plasma membrane and bacterial/yeast intracellular membranes?
-mammalian - driven by Na+ gradients
-bacteria/yeast - driven by H+ gradients
Describe the transcellular transport of glucose
-moves against conc. grad.
-driven by glucose/Na+ symporter at apical surface - coupled uptake of glucose
-results in high Na+ conc. in cell that prevent symporter working
-Na+ moves out of cell into blood by Na+/K+ pump at basal surface
-high glucose conc. in cell - moves into blood using glucose carrier at basal surface
