FCELL- Membrane structure Flashcards
why are biological membranes bilayers
composed of lipids and proteins
lipids are amphipathic meaning they have a hydrophobic and hydrophilic part
due to this they will orientate themselves with the hydrophobic portion on the inside and the hydrophobic portion on the outside - forming a bilayer
describe the lipid composition of the biological membrane
polar head group
phosphate bridge links head and glycerol backbone
fatty acid hydrophobic tail
describe the cholesterol component of the biological membrane
regulate membrane fluidity
hydrophilic head molecule
describe the ceramide component of the biological membrane
attaches to fatty acids with sphingosine head
combined with carbohydrate and becomes a glycolipid
combined with a phosphate group and choline group forms sphingomyelin
known as sphingolipids
describe the distribution of molecular membrane components
cholesterol is distributed evenly between inner and outer membrane
other components distributed asymmetrically
PC, SM- expressed extracellularly
PS, PE, PL - expressed mainly intracellularly
outline membrane synthesis of lipids
new synthesis of lipids in ER
mature as they move to the golgi
transferred to cell surface
enzymes involved in synthesis - present in the cytosol
to redistribute the lipids they have to be transported from one side of the membrane to the other - energetically unfavourable (pass through hydrophobic region)
done via ABC transporter - ATP binding cassette transporters - allows travel though the membrane - requires energy and enzymes
outline membrane synthesis of lipids
new synthesis of lipids in ER
mature as they move to the golgi
transferred to cell surface
enzymes involved in synthesis - present in the cytosol
to redistribute the lipids they have to be transported from one side of the membrane to the other - energetically unfavourable (pass through hydrophobic region)
done via ABC transporter - ATP binding cassette transporters - allows travel though the membrane - requires energy and enzymes
outline the function of flippase, floppase and scramblase
floppase - move phospholipids from the inner to the outer leaflet
flippase - move phospholipids from outer surface to the inner leaflet
scramblase - bidirectional movement
describe integral membrane proteins
single / multi pass
strong non-covalent bonds
trans-membrane domain often an alpha helix
can be predicted from sequence
describe peripheral membrane proteins
located on both extracellular and cytosolic membrane
associated by non-covalent bonds
complex interactions (e.g., can act with surface of the memrbane and integral protein)
describe lipid anchored membrane proteins
covalently linked to a lipid molecule such as glycosyl- phosphatidylinositol
describe lipid anchored membrane proteins
covalently linked to a lipid molecule such as glycosyl- phosphatidylinositol
describe the role of cholesterol in membrane fluidity
low temperature - lipid packs tightly together
increased cholesterol can reduce interactions between lipids in the membrane therefore at lower temperatures cholesterol increases membrane fluidity
high temperature-
higher energy lipids are more motile
cholesterol helps to stabilise by maintain some interactions between lipids - therefore cholesterol acts to decrease fluidity - prevents movement
what are the consequences of increases cholesterol
spur cell anaemia - increased cholesterol = decrease membrane fluidity - reduces flexibility meaning RBC get trapped in capillaries - rupture leading to anaemia
describe passive diffusion
rate of uptake is dependent on solute concentration
move from a region of higher concentration to a low concentration
carrier mediated - a small change in concentration = sharp increase in rate of uptake
