L15 - Structure and function of cell membrane Flashcards
(16 cards)
Describe the fluid mosaic model
“Sea of lipids in which proteins can move freely”
Membrane is 50% lipid and 50% protein, held together by hydrogen bonds
What are phospholipids
Comprises 75% of lipids
Each molecule is amphipathic
Describe the heads of phospholipids
Phosphate, polar head
Describe the tails of phospholipids
Lipid, non-polar tail
What factors determine fluidity of the membrane
Lipid tail length - the longer the tail, the less fluid the membrane
Number of double bonds - more double bonds increases fluidity
Amount of cholesterol - more decreases fluidity
Describe integral proteins
Extend into or completely across cell membrane (also called transmembrane proteins)
Describe preipheral proteins
Attatched to either inner or outer surface of cell membrane and are easily removed from it
What is the lipid bilayer permeable to
Nonpolar, uncharged molecules (O2, N2)
Lipid soluble molecules (steroids, fatty acids)
Small uncharged polar molecules (water, urea, glycerol, CO2)
What is the lipid bilayer inpermeable to
Large uncharged polar molecules (glucose, amino acids)
Ions (Na+, K+, Cl-, Ca2+, H+ etc.)
What are the extracellular ion concentrations
High Na+, Low K+, High Cl-
What factors affect diffusion rate
Concentration gradient
Temperature
Size of diffusing substance
Surface area of diffusing substance
Diffusion distance
What 2 factors affect membrane permeability to water
Permeability through lipid bilayer (Pd)
Peremability through water channel (Pf)
What are the intracellular ion concentrations
Low Na+, High K+, Low Cl-
What are the properties of Pd
Small
Mercury insensitive
Temp dependent (lipid fluidity)
What are the properties of Pf
Large
Mercury sensitive
Temp independent
Mediated by aquaporins
Why do cells have different Pw
Pf is mediated by the aquaporins
Cells express different aquaporin isoforms (9 isoforms)
