(05) Structure and Function of Cell Membrane

Question 1

model used to describe membranes

Answer 1

fluid mosaic model
sea of lipids, proteins float like icebergs

Question 2

composition of PM

Answer 2

50% lipid, 50% protein

Question 3

Name the three types of lipids involved in the plasma membrane

Answer 3

Cholesterol / Glycolipids scattered amongst double row of phospholipid (75%) molecules

Question 4

molecular architecture of PM

Answer 4

made of amphipathic phospholipids
polar heads outside, non-polar tails form hydrophobic core that is highly impermeable to the passage of charged ions

Question 5

factors affecting the fluidity of PM

Answer 5

lipid tail length (longer=more structured=less fluid)
# double bonds (more double bonds = more fluid)
amount of cholesterol (more decreases fluidity)

Question 6

two types of membrane proteins + describe

Answer 6

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

Question 7

list the functions of membrane proteins

Answer 7

receptors
cell identity markers
linkers
enzymes
ion channels
transporter proteins

Question 8

what is the lipid bilayer permeable to

Answer 8

Nonpolar, uncharged molecules: O2
Lipid soluble molecules: steroids, fatty acids
small uncharged polar molecules: H2O, Urea, CO2

Question 9

what is the lipid bilayer impermeable to

Answer 9

Large uncharged polar molecules
eg. Glucose / amino acids
charged ions

Question 10

what factors do the rate of diffusion depend on

Answer 10

greater difference in concentration = faster
higher temp = faster
surface area available for exchange
larger size of diffusing substance = slower
larger distance of diffusion = slower

Question 11

describe electrochemical gradients

Answer 11

chemical = conc grad
electrical = ions influenced by membrane potential AS WELL AS concentration gradient

Question 12

relative extracellular vs cytoplasmic concentrations of Na+

Answer 12

HIGH outside cell
LOW inside cell

Question 13

relative extracellular vs cytoplasmic concentrations of K+

Answer 13

LOW outside the cell
HIGH inside cell

Question 14

relative extracellular vs cytoplasmic concentrations of Cl-

Answer 14

same as Na+
HIGH outside, LOW inside

Question 15

describe osmosis

Answer 15

net movement of water through selectively permeable membrane from high H2O conc to low conc
water moves to eliminate osmotic gradient

Question 16

“equation” for membrane permeability to water

Answer 16

Pw = Pd + Pf
Permeability to water = Pd (through lipid bilayer) + Pf (through water channel)

Question 17

what are water channels mediated by

Answer 17

aquaporins
there are 9 isoforms
cells have different Pw bc they express different isoforms

Question 18

what does the permeability of a molecule depend on

Answer 18

size
charge
lipid solubility

Question 19

Cells use about 30% of resting energy to…

Answer 19

maintain concentration and electrical gradients

Question 20

define osmotic pressure

Answer 20

the hydrostatic pressure applied to oppose osmosis
(a colligative property - depends only on NUMBER and not type of particles in the solution)

Question 21

How can osmolarity to calculated?

Answer 21

from the concentration of solution and knowledge of ionisation properties

Question 22

osmolarity of body fluids

Answer 22

about 280 mOsmol

Question 23

define tonicity

Answer 23

the effect a solution has on cell volume
DEPENDS ON MEMBRANE PERMEABILITY OF SOLUTE

hypotonic –> swelling / lysis (haemolysis)
hypertonic –> shrinkage (crenation)