transport across cell membrane Flashcards
describe phospholipids
hydrophilic heads of both layers point to the outside of the CSM attracted to the water on both sides, hydrophobic tails of both layers point into the centre of the CSM, repelled by water on both sides
what are the functions of the CSM proteins?
provide support, act as carriers for substances, to help cells stick together, act as receptors
what are extrinsic proteins?
on the surface but only partly embedded, they give mechanical support to the cell/act as receptors for molecules such as hormones
what are intrinsic proteins?
completely span membrane, act as carriers to transport material across the CSM, others can be enzymes
what are glycolipids?
cell surface receptors for hormones and neurotransmitters, allow cell-cell recognition, helps cells attach to each other
what does cholesterol do?
adds strength/rigidity to the CSM by pulling the fatty acid tils of the phospholipids together, reduces membrane fluidity at high temps, prevents water leakage from the cell
why is the arrangement of the CSM referred to as the fluid mosaic model?
the phospholipids can move relative to one another, the proteins can vary in size and shape like the tiles in a mosaic
what factors affect diffusion?
concentration gradient, length of diffusion pathway, surface area, temperature
definition of diffusion
movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached
how to work out diffusion rate
surface area x concentration difference divide by lenth of diffusion pathway
what prevents molecules from passing through the CSM?
not lipid soluble, very large, polar
what is facilitated diffusion?
diffusion made easier by the use of channel and carrier proteins that span the CSM
what are protein channels?
protein pores that open or close to control the passage of selective ions e.g. sodium/potassium
what are carrier proteins?
take substances from one side of the membrane to the other
how does the number of proteins in the CSM limit the rate of diffusion?
proteins become saturated and can’t support any more molecules
what happens to the permeability of the CSM in very cold temperatures?
phospholipids don’t have much energy and can’t move much so they’re tightly packed together, making the membrane rigid. proteins denature, increasing permeability as proteins lose structure and function. ice crystals form, pierce through membrane making it highly permeable
what happens to the permeability of the CSM in warm temperatures?
phospholipids can move around, not as tightly packed together - membrane is partially permeable. as temp increases the phospholipids move more as they have more energy, increases the permeability
what happens to the permeability of the CSM in hot temperatures?
phospholipid bilayer starts to break down/melt and membrane becomes more permeable. water inside the cells expands, putting pressure on the membrane. proteins denature so can’t control what enters/leaves the cell - increases permeability
definition of osmosis
water moves from an area of high water potential to low water potential across a semi-permeable membrane until equilibrium is reached
water potential of pure water
zero
what is water potential measured in?
kilo-pascals (KPa)
what is water potential?
a measure of how easy it is for water to move
what happens with animal cells are placed in a higher water potential?
red blood cells - absorb water by osmosis when placed in water as it has a higher water potential. has a very thin CSM that can’t stretch to a great extent, so CSM breaks, bursting the cell and releasing its contents…. HAEMOLYSIS
how do animal cells stop haemolysis from happening?
they usually stay in a liquid which has the same WP as the cell
