(05) Structure and Function of Cell Membrane Flashcards
model used to describe membranes
fluid mosaic model
sea of lipids, proteins float like icebergs
composition of PM
50% lipid, 50% protein
Name the three types of lipids involved in the plasma membrane
Cholesterol / Glycolipids scattered amongst double row of phospholipid (75%) molecules
molecular architecture of PM
made of amphipathic phospholipids
polar heads outside, non-polar tails form hydrophobic core that is highly impermeable to the passage of charged ions
factors affecting the fluidity of PM
lipid tail length (longer=more structured=less fluid)
# double bonds (more double bonds = more fluid)
amount of cholesterol (more decreases fluidity)
two types of membrane proteins + describe
integral / transmembrane: amphipathic, hydrophobic regions (usually non-polar amino acid helices) in hydrophobic bilayer core, hydrophilic ends interact w/ aq slm
N-terminus on extracellular side, C-ter,omis on cytoplasmic side
peripheral: attached to inner/outer surface
list the functions of membrane proteins
receptors
cell identity markers
linkers
enzymes
ion channels
transporter proteins
what is the lipid bilayer permeable to
Nonpolar, uncharged molecules: O2
Lipid soluble molecules: steroids, fatty acids
small uncharged polar molecules: H2O, Urea, CO2
what is the lipid bilayer impermeable to
Large uncharged polar molecules
eg. Glucose / amino acids
charged ions
what factors do the rate of diffusion depend on
greater difference in concentration = faster
higher temp = faster
surface area available for exchange
larger size of diffusing substance = slower
larger distance of diffusion = slower
describe electrochemical gradients
chemical = conc grad
electrical = ions influenced by membrane potential AS WELL AS concentration gradient
relative extracellular vs cytoplasmic concentrations of Na+
HIGH outside cell
LOW inside cell
relative extracellular vs cytoplasmic concentrations of K+
LOW outside the cell
HIGH inside cell
relative extracellular vs cytoplasmic concentrations of Cl-
same as Na+
HIGH outside, LOW inside
describe osmosis
net movement of water through selectively permeable membrane from high H2O conc to low conc
water moves to eliminate osmotic gradient
