2.5 biological membranes Flashcards
state the role of membranes
partially permeable barriers between the cell and its environment, between organelles and
the cytoplasm and within organelles
sites of chemical reactions
sites of cell communication (receptors, cell signalling, cell reconition).
what is the fluid mosaic model
Phospholipid bilayer
Hydrophobic tails , hydrophilic heads
Proteins scattered
proteins and phospholipids are free to move
model that shows arrangement of biological membranes
name the components in the fluid mosaic model
phospholipid
intrinsic proteins(carrier,channel)
extrinsic proteins
glycoproteins
glycolipids
cholesterol
what is a micelle
one layer of phospholipids, creates sphere shape
whats a bilayer
two layers of phospholipids
describe channel proteins
have pores that act as channels to allow ions to pass through
describe carrier proteins
change shape using ATP to carry specific molecules across membrane
describe extrinsic proteins
found on the surface
provides mechanical support and act as cell receptors for hormones etc.
describe glycolipids
carbohydrate chain attached to phosholipid
role in cell recognition and act as cell markers or antigens
describe glycoproteins
carbohydrate chain attached to protein molecule
receptors for chemical signals/hormones/toxins
role in cell adhesion
describe cholesterol
4 carbon based rings in fatty acid tail layer
provides mechanical stability and flexibility
restricts movement of membrane etc
how does cholesterol affect membrane permeability
buffers the effect of lower temperature by preventing phospholipids getting too close = prevents reduction in fluidity
what is simple diffusion
the net movement of particles down a concentration gradient from an area of higher conc. to lower conc.
what molecules does simple diffusion allow to cross membranes
small polar or non polar
what is facilitated diffusion
diffusion using proteins (carrier or channel)
what molecules does facilitated diffusion allow to cross membranes
large or polar molecules
what factors affect the rate of simple diffusion (+facilitated diffusion)
conc. gradient
temperature
surface area
diffusion distance
+more intrinsic proteins
what is passive transport
no energy needed from ATP
how do molecules move down/up concentration gradients
kinetic energy
what do active transport require
energy needed from ATP
what is active transport
movement of substances against their concentration gradient using ATP and carrier proteins
what is bulk transport and name two examples
transport of large molecules too large to pass through membrane
endo and exocytosis
what is endocytosis
bulk transport of molecules into the cell
segment of membrane surrounds and encloses particle into a vesicle
name the different ways of endocytosis and what they move
phagocytosis - solids
phinocytosis - liquids
what is osmosis
net movement of water molecules down their water potential gradient across a partially permeable membrane
what is water potential
the tendency of water molecules to diffuse/move from one region to another
what is the highest water potential
pure water 0kPa
what is osmotic concentration
the amount of dissolved solutes in a solution
what do a higher and lower osmotic concentration do to the water potential
higher osmotic conc= lower water potential = concentrated solution
lower osmotic conc= higher water potential = dilute solution
what is a hypertonic solution
has a higher osmotic conc. to the inside of cell so water moves out of cell and shrinks
what is an isotonic solution
an equal osmitic/ water potential conc. inside and outside of cell
what is a hypotonic solution
has a lower osmotic concentration to inside the cell so water moves in and cells expand
what factors affect membrane structure and permeability
temperature
solvents
how does increasing temperature affect membranes
increased temp = more kinetic energy = molecules move faster = permeability/ fluidity increases
how does a drop in temperature affect membranes
saturated fatty acids become compressed= unsaturated fatty acids with kinks = maintain fluidity
how does temperature below freezing pint affect membranes
water freezes = expands = pierces/ forces apart closely packaged rigid layer = permeability increases
what determines membrane fluidity at cold temperatures
proportions of unsaturated and saturated fatty acids
how does a solvent affect membranes
organic solvents (acetone, ethanol) will damage membranes = dissolve lipids
how does increasing temperature affect proteins in membranes and permeability
vibrates more= breaks hydrogen and ionic bonds = tertiary structure changes/ denatures = more permeable
