What does the plasma membrane cover?
the cell membrane along with all the organelle membranes
what are membranes?
a phospholipid bilayer
Which way to the heads and tails face in the phospholipid bilayer?
Hydrophilic heads point outwards and hydrophobic tails point inwards
what is an intrinsic protein?
- hydrophobic r groups interact with hydrophobic fatty acid tails
- channel protein - allows polar molecules and ions through e.g. glucose and water
- glycoproteins - cell signalling e.g. neurotransmitter of hormone receptors
- pass through both layers of the phospholipid bilayer
What are extrinsic proteins?
- hydrophilic r group holds them on one side of the bilayer
- examples include: enzymes, receptors, assembly and stabilisation of other proteins e.g. PSII
- receptor and adhesion proteins
Function of membranes:
- acts as a barrier between areas
- cell signalling
- site of chemical reactions
- DOES NOT provide support for cell
How does temperature effect membrane permeability?
increased temp leads to phospholipids with more kinetic energy (fluidity and permeability increase). Membrane proteins also begin to denature so membrane structure breaks down (permeability increases)
How does fatty acid saturation effect membrane permeability?
unsaturated fatty acids have double bonds - introduces a kink in the tail - phospholipids are further apart so increased permeability
How does cholesterol effect membrane permeability?
the presence of cholesterol increase membrane permeability, but also stabilises membranes at higher temperatures
How do solvents effect membrane permeability?
- increased permeability (leakage)
- organic solvents will dissolve solutes
usually less polar than water so reduces hydrophobic/hydrophilic interactions
Example of how solvents effect membrane permeability:
- alcohol/ethanol = at low concs, ethanol moves between phospholipids. At high concs, phospholipids dissolve
What is diffusion?
the net movement of particles from high to low concentration (down the concentration gradient)
Is diffusion a passive process?
YES
needs no extra energy (apart from kinetic energy of particles)
What happens to diffusion at equilibrium?
concentration gradient is at 0 so no net diffusion, rate = 0
What is rate?
rate refers to time. Time taken for a process to occur e.g. short time = fast rate
What are the five factors effecting diffusion?
- temperature - higher temp = higher kinetic energy
- concentration gradient - steeper gradient increases rate
- surface area - greater surface area increase rate
- diffusion distance - smaller distance increases rate
- molecular mass - smaller molecules increases rate
diffusion through membranes (non-polar molecules):
diffuse through membrane e.g. pass between phospholipids
diffusion through membranes (polar molecules):
hydrophobic fatty acid tails repel polar molecules - diffusion is very slow e.g. water, ethanol and ammonia
diffusion through membranes (facilitated diffusion):
facile - easy, without any difficulty, involves membrane proteins
Channel proteins:
- pore provides easier route for polar molecules to diffuse through
carrier proteins:
- molecule binds to protein, carrier protein changes shape allowing molecule to to pass through membrane
what is osmosis?
net movement of water molecules from high to low concentration, through s partially permeable membrane - water conc is measured by WATER POTENTIAL (psi)
what happens in osmosis?
In osmosis water moves towards the more negative water potential - still down the water potential gradient
hypertonic solution:
cell gains mass as water enters by osmosis - cell has a more negative water potential than the solution. Cell becomes turgid
