MCB L2 Flashcards
State the function of plasma membranes
Enclose cell
Allows essential difference between cytosol + external environment
Impermeable - allows controlled access to inside cell
State the function of ion gradients across membranes
Synthesis of ATP
Transport of selected solutes
Transmission of electrical impulses
Descibe the structure of the cell membrane
Phospholipids
Proteins
(50:50)
Hydrophillic heads face outwards, hydrophobic tails face inwards
Creates a double bilayer - bimolecualr leaflet
Cell membranes are plastic + deformable + mobile
Fluid dynamic structure - lipid molecules move freely about the plane - rarely flip
Describe the function of proteins in cell membranes
Form structural links with cytoskeleton - cytoskelton anchors components of cell membrane and keeps membrane rigid
Describe the structure of phospholipids
Phosphate head - choline group linked to glycerol group via phosphate group
TWO hydrocarbon hydrophobic fatty acid tails
One tail = fully saturated (straight) One tail = unsaturated (1/ more cis double bond, giving it a kinked profile)
State the structural significance of one of the hydrocarbon fatty acid chains of the phospholipid having a “kinked” profile
Prevents phospholipids from becoming too closely packed together
Allows fluid dynamic membrane
Describe the formation of liposomes
Type of spherical vesicle
- Phospholipids placed in water, phospholipids aggregate (automatically arrange themselves) into bimolecular sheets - double bilayer of phospolipids where hydrophobic fatty acid tails are facing inwards away from water and the hydrophillic heads are facing towards the water
- Liposomes formed, separates the two aqueous phases
Why do we have charge assymetry?
Different components inside and outside membranes, therefore, charge assymetry
State 3 enzymes involved in mantaining membrane assymetry
- Flipases
- Flopases
- Scramblases
State the function of flippases
Transfer / move / “flip” phospholipids from inner lumen to outer side / cystolic side of membrane
Specific flippases for specific phospholipids
State the function of floppases
Transfer / move / “flip” phosphollipids from outer sode / cystolic side of membrane to inner lumen
State the function of scramblases
Ensure equal number of phospholipids on both sides of bilayer by random transfer of phospholipids between each monolayer (inner layer and outer layer)
Diagram showing enzymes maintainining membrane assymetry
RECOGNISE FUNCTIONS OF:
- Flippase
- Floppase
- Scramblase
Breifly describe the structure of glycolipids
Sugar containing lipid molecule
Sugar group orientated towards outside of cell
State the function of gangliosides
Type of glycolipid
Has attached oligosachharides
Important role in surface of nerve cells
Ganglioside Gm1 - acts as surface receptor to bacterial toxin which causes cholera
State the function of cholestrol in membranes
Found in eukaryotic plasma membranes only
Oriente / fit between phospholipids in bilayer, hydroxyl heads of cholestrol are close to polar head groups of phosholipids
‘
PARTIALLY IMOBILISING PHOSPHOLIPID MOLECULES This leads to membrane becoming more rigid, less fluid, less permeable, less deformable
(ACTS AS A SPACER) Prevents phase transitioning in membranes - prevents membrane from freezing
State 2 factors which affect the fluidity of the phospholipid membrane
- Fatty acid chain length - shorter fatty acid chain length means the chains are less likey to interact with each other, more fluidity
- Cis double bonds - higher number of cis bonds = more kinks = phospholipids less closely packed, more cholestrol can fit “snugly” in between - membrane spacer - preventing phase transitions (prevents membranes from freezing), allowing membranes to be fluid at lower temperatures
What is glycocalyx?
Carbohyrdate rich zone on surface of cell
Consists of
Glycolipids
Oligosaccharides
Selectins
Proteins that bind to the cell surface and mediate cell-cell adhesions
Provide surface markers used to identify certain cells
State 4 membrane proteins and their functions
Transporters: transport ions, metabolites, nutrients
Anchors: Anchor membrane to macromolecules
Receptors: Detect external signals
Enzymes: Carry out specific reactions
State 2 membrane proteins found in red blood cell membranes and their functions
Spectrin - cytoplasmic side of membrane
Ankyrin - inner side of membrane - links ankyrin to transmembrane proteins
BOTH - give RBC characteristic shape
State 4 protein-membrane associations
Transmembrane
Lipid-linked
Protein attached
Monolayer associated
