cell membranes Flashcards
describe plasma membranes?
( surface of cells )
barrier between the cell + its environment - controls what enters + exits
partially permeable - only let some molecules through
can move by active transport / diffusion / osmosis
what do plasma membranes do?
allow recognition by other cells
allow cell communication
describe membranes withing the cell?
membranes around the organelle
partially permeable
what do membranes within the cell do?
divide the cell into compartments - barrier between organelle + cytoplasm - functions more efficient as reactions kept inside
form vesicles to transport substances between different areas of cell
control what enters + exits organelle
site of chemical reactions
e.g inner membrane of mitchondrian - enzymes for respiration
what do membranes within the organelle do?
act as a barrier between membrane contents + rest of organelle
e.g thylakoid membranes
what do phospholipid molecules form?
bilayer - double layer
why are cell membranes described as having a fluid mosaic structure?
phospholipids always moving so bilayer fluid
protein molecules scattered through bilayer like a mosaic
what are glycoproteins + glycolipids?
glycoproteins - intrinsic proteins with a polysaccharide chain attached
embedded in cell surface membrane
glycolipids - extrinsic lipids with a polysaccharide chain attached
what are the functions + properties of phospholipids?
barrier to dissolved substances
head - hydrophilic
tail - hydrophobic
bilayer - heads face outwards
centre of bilayer - hydrophobic - barrier to water soluble substances
what are the functions + properties of cholesterol?
gives membrane stability
lipid in all cell membranes
fit between phospholipids - bind to tails - tails pack closely - membrane less fluid + more rigid
lower temps - prevents phospholipids packing closely - increases fluidity
what are the functions + properties of proteins?
controls what enters + exits
form channels - allow small / charged particles through
carrier proteins transport molecules + ions across membrane by active transport + facilitated diffusion
act as receptors for molecules in cell signalling
when a molecules binds to protein - triggers chemical reaction
what are the functions + properties of glycolipids + glycoproteins?
acts as receptors for messenger molecules
form hydrogen bonds with surrounding water molecules - stabilises membrane
site of where drugs, hormones, antibodies bind
antigens - cell surface molecules involved in immune response
what is cell signalling?
how cells communicate
how does cell signalling work?
a cell releases a messenger molecule
molecule travels to another cell
molecule detected by cell as binds to a receptor on its cell membrane
how do cell membrane receptors play an important role in cell signalling?
receptor proteins have specific shape - only messenger molecule with complementary shape can bind
different cells have different types of receptors
what is a target cell?
a cell that responds to a particular messenger molecule
how does the messenger molecule glucagon work?
hormone released when not enough glucose in blood - binds to receptors on liver cells - liver cells break down turning glycogen into glucose
what do drugs do when they bind to cell membrane receptors?
trigger a response in cell / block receptor + prevent it from working
how do antihistamines work?
histamines released when cell damaged
binds to receptors on surface of other cells - inflammation
antihistamines block histamine receptors - stops inflammation
how do you investigate how temperature affects the permeability of the cell membrane?
cut 5 equal pieces of beetroot + rinse to remove pigment released when cutting
put each piece in a different test tube + 5 cm water
put each test tube into a water bath at a different temperature ( 10, 20, 30 etc. ) for same length of time
remove beetroot from each tube leaving water
use calorimeter - the higher the permeability of the membrane - more pigment released
how does permeability change when temp below 0C?
below 0C - phospholipids can’t move as little energy - rigid membrane
channel + carrier proteins deform - increases permeability of membrane
ice crystals can form + pierce membrane - highly permeable
what are the 2 types of protein in the membrane?
intrinsic proteins - go through both layers of phospholipids
extrinsic proteins - one side of bilayer only
what are the 2 intrinsic proteins + give properties?
carrier - passive + active transport
involves
how does permeability change when temp is between 0 and 45C?
phospholipids can move around as not packed as tight - partially permeable membrane
as temp increases - phospholipids move more as more energy - increases permeability
how does permeablity change when temp above 45C?
phospholipid bilayer melts + membrane more permeable
water inside cell expands so pressure on membrane
channel + carrier proteins deform - can’t control what enters / exits - increases permeability
how does the solvent surrounding cells affect membrane permeability?
increases permeability as they dissolve lipids in cell membrane - loses its structure
how can you change the solvent to increase membrane permeability?
increase the concentration of solvent
what are the 2 main types of protein in the membrane?
intrinsic proteins - go through both layers of phospholipid bilayer
extrinsic proteins - go through one side of bilayer only
what are carrier proteins?
proteins that use active + passive transport
( down a concentration gradient )
uses shape of protein to change ( open / close door )
what are channel proteins?
proteins with a hole ( channel )
hydrophilic channel - allows passive movement of polar molecules + ions down a concentration gradient
held in position by interactions between hydrophobic core of membrane + hydrophobic outside of protein
what is diffusion?
net movement of particles both ways from an area of high concentration to low concentration until even distribution
passive process - no energy needed
what is the concentration gradient?
path from an area of high concentration to low concentration
what diffuses through cell membranes?
small, non polar molecules - carbon dioxide + oxygen between spaces in phospholipids
water small enough so fits even if polar
what 4 factors does the rate of diffusion depend on?
concentration gradient - higher = faster rate
thickness of exchange surface - thinner means particles have a shorter distance to travel = faster rate
surface area - larger = faster rate
temperature - warmer = faster rate as particles have more kinetic energy so move faster
