membranes

Question 1

made of lipids: fats and oils
∙structural- phospholipids, sterols, waxes
∙storage- triglycerides

TRIGLYCERIDES:
made from 3 fatty acids + glycerol
2 types of fatty acids= saturated + unsaturated

SATURATED= single bond
UNSATURATED= double bond

Answer 1

Phospholipids:
∙major component of cell membrane
∙polar (hydrophilic) and non-polar (hydrophobic)
∙can from 3 main structures: micelle, vesicle, bi-layer

∙more saturated fatty acids= more solid
∙more unsaturated fatty acids= more fluid

Sterols:
∙cholesterol in animals
∙stiffen membranes
∙have polar and non-polar heads

Question 2

Dancing lipids (fluid mosaic):
∙hydrophobic tails constantly moving along the membrane (move at 1 micro metre/ second)
∙crossing to the other side of the membrane is hard, as polar head would have to push through hydrophobic interior

Answer 2

membranes contain proteins:
proteins have polar and non-polar regions too
hydrophilic regions contact the polar head groups, hydrophobic regions contact the lipid tails

Question 3

TRANSPORT:
biological membranes are selectively permeable

permeability of lipid bilayer:
permeable= gas, small uncharged polar molecules (e.g. ethanol), partly water

impermeable= ions, large uncharged polar molecules (e.g. glucose), charged polar molecules (e.g. ATP)

Answer 3

membrane transport proteins:
transporters: binding + shape change

channels: diffusion mostly, some are gated and charged

passive or active transport

simple diffusion= semi-permeable membrane, rate of flow depends on conc difference

CHARGE AND CONCENTRATION:
both matter in transport
electrochemical gradient is a combination of charge + concentration

Na+K+ pump: maintains ion gradients, creates resting potential, pumps 3Na+ in, 2K+ out

osmosis:passive diffusion of water across a selectively permeable membrane
water moves from low solute conc to high solute conc