Topic 2 -Cell Membranes Flashcards
What are the functions of phospholipids in the phospholipid bilayer
Cell membranes
- The fatty acid tails are hydrophobic so face inwards
- the phosphate heads are hyrdophillic so face outwards towards the water
- it allows lipid soluble substances to pass through but prevents water soluble substances from moving through.
- It also allows the membrane to be flexible and self sealing.
Describe a cell surface membrane’s permeability
Cell membranes
Its selectively permeable as it allows lipid soluble substances to pass through but prevents water soluble substances from moving through
What’s the model used for cell surface membranes ?
Cell membranes
The fluid mosaic model - its fluid because phospholipids are constantly moving and the size and pattern of the bilayer is mosaic like and proteins are scattered through like a mosiac.
what are extrinsic proteins ?
Cell membranes
Proteins that do not span the whole bilayer, e.g. receptor proteins
What are intrinsic proteins ?
Cell membranes
Proteins that span the whole bilayer, e.g. channel proteins/ carrier proteins
What are channel proteins function ?
Cell membranes
They form pores in the membrane to allow large molecules, or polar molecules to pass through
What are carrier proteins functions ?
Cell membranes
Bind to larger molecules or ions like glucose and amino acids , then change shape in order to move these across the membrane.
What are the functions of cholesterol in the cell membrane ?
Cell membranes
- Adds strength.
- They’re very hydrophobic so prevent loss of water and dissolved ions from the cell.
- They fit in between the phospholipids and bind to the tails causing them to pack more closely together, making the membrane more rigid and less fluid by restricting movement.
- Maintains the shape animal cells (with no cell wall).
What are the functions and structure of glycolipids ?
Cell membranes
- Contain a carbohydrate chain covalently bonded with a lipid.
- This acts as a cell surface receptor for chemical.
- They help maintain the stability of the membrane.
- They act as recognition sites to help cells attach to each other to form tissues.
What’s the function and structure of glycoproteins ?
Cell membranes
- Carbohydrate chains attached to extrinsic proteins covalently.
- They act as cell surface receptors, more specifically for hormones and neurotransmitters.
- They act as recognition sites to help cells attach to form tissues,
What happens to a cell surface membranes permeability in temperatures below 0 degrees ?
Cell membranes
- Phospholipidss dont have much kinetc enegery so they cn’t move very much
- they’re packed cloely together making the membrane rigid.
- Channel and carrier proteins deform, increasing permeability.
- Ice crystals may form and peirce the membrane, making permeability increase when it thaws.
What happens to a cell surface membranes permeability in temperatures between 0 and 45 degrees ?
Cell membranes
- Phospholipids can move around more as they aren’t packed as closely together-the membrane is partially permeable.
- As temperature increases, the phospholipids move more as they’re given more energy.
- This increases the permeability of the membrane.
What happens to a cell surface membranes permeability in temperatures above 45 degrees ?
Cell membranes
- The phospholipid bilayer begins to melt and the membrane becomes permeable.
- Water in the cell expands, putting pressure on the membrane.
- Channel and carrier proteins deform-they cannot control what enters of exits the cell so the permability increases.
How would you investigate the permability of beetroot at different temperatures ?
Cell membranes
- use a scapel to cut 5 identical peicies of beetroot and rinse them.
- Place them each in their own test tube with 5cm3 of water (using a measuring cylinder).
- Place each test tube in a different water bath of doffernt temperaures (10,20,30,40 and 50 degrees) for 20 minutes (using a stopwatch).
- Remove the beetroot.
- Use a colorimeter - a machine that passes light thorugh liquid and measures how much light is aborped, the more absorption, the more pigment, the more permeable the membrane.
- connect the colorimetre to a computer to collect the data.
What’s the definnitoin of diffusion ?
Cell membranes
The net movement of molecules or ions from an area of higher concentration to an area of lower concentation down the concentration graident.
When does the process of diffusion stop ?
Cell membranes
Once equilobrium is reached - an even distibution of particles.
What type of particles move across the membrane by simple diffsuion ?
Cell membranes
small and non polar molecules as it makes them lipid soluble.
Is energy required for simple diffusion ?
Cell membranes
No, its passive.
When is facilitated diffusion used and what happens ?
Cell membranes
For larger moleucle (like glucose and amino acids) and polar molecules as this makes them water soluble but the centre of the phospholipid bilayer is hydrophobic, so instead these particles diffuse through channel or carrier proteins.
What does the rate of simple diffusion depend on ?
Cell membranes
- the higher the concentration gradient, the faster the rate of diffusion.
- The thinner the exchange surface the faster the rate as there’s less distance for particles to travel across.
- The larger the surface area, the faster the rate as more particles can diffuse at once.
What are microvilli ?
Cell membranes
projections formed by the cell sirface membrane folding up on itself (e.g. eithelial cells), they give the cell a larger surface area so increase the rate of diffusion.
What does the rate of facillitated diffusion depend on ?
Cell membranes
- The higher the concentration gradient, the faster the rate of diffusion.
- the more channel and carrier proteins the faster the rate as once all proteins are occupied the rate of diffusion cannot go any faster.
- the higher the concentration gradient, the faster the rate of diffusion.
- The thinner the exchange surface the faster the rate as there’s less distance for particles to travel across.
- The larger the surface area, the faster the rate as more particles can diffuse at once.
Why will the rate of diffusion slow down over time.
Cell membranes
The concentration of the particle insdie and outside of the cell will reach eqiilibrium.
What’s osmosis ?
Cell membranes
The net diffusion of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane down the concentration gradient.
