2.1.5 Biological membranes Flashcards
Describe the fluid mosaic model of membranes
Fluid = phospholipid bilayer in which individual phospholipids can move
Mosaic = different components within the membrane
Explain the role of phospholipid bilayer
hydrophilic phosphate head pointing outwards and hydrophobic fatty acid tail pointing inwards.
Partially permeable barrier - barrier to large/polar molecules and allow small/non-polar molecules to pass through.
Explain the role of cholesterol and glyco-lipids in membranes
Cholesterol = maintains stability of the phospholipid bilayer
Glycolipids = cell signalling and recognition
Explain the role of extrinsic proteins (glyco-proteins)
Cell signalling and cell binding.
Glycoproteins = antigens
Explain the function of intrinsic proteins
Channel proteins for facilitated diffusion
Carrier proteins for facilitated diffusion and active transport
Electron carriers in respiration and photosynthesis
The function of membranes within a cell
Partially permeable barrier between organelles and the cytoplasm, compartmentalisation.
Isolates contents within organelles.
Site for chemical reactions e.g. the attachment of enzymes and ribosomes
The function of cell-surface membranes.
Partially permeable barrier between the cell and its environment.
Site for cell communication - cell signalling
Site for chemical reactions.
What is the role of membrane bound receptors?
Sites where signal molecules, e.g. hormones and drugs, can bind.
What is meant by cell signalling
Communication between cells
Explain how cell surface membranes contribute to cell signalling
Signal molecule is released from cell by exocytosis/secretion.
Glycoproteins/ glycolipids on the cell surface membrane act as receptors receptors/signal molecule are specific and complementary to each other
The attachment of the signal molecule causes a change to the cell.
Name and explain how the factors that affect membrane permeability.
Temperature: denatures proteins and phospholipids gain kinetic energy and move apart.
pH: denatures proteins
Solvent use: dissolves the membrane
How colorimetry is used to investigate membrane permeability
- Use plant tissue with soluble pigment within the cell. more permeable membrane = more pigment in solution.
- Select colorimeter filter
- Use distilled water to set colorimeter to 0, and measure absorbance.
- High absorbance = more pigment in solution and more permeable membrane.
Define osmosis
The net movement of water down the water potential gradient across a partially permeable membrane
What are the routes in which water can enter a cell through the phospholipid bilayer?
Between phospholipids in the phospholipid bilayer.
Through channel proteins
Define water potential
Pressure created by water molecules measured in kPa
The water potential of pure water = 0
More solute = more negative water potential
How does osmosis affect plant and animal cells
osmosis into the cell
Plant cells - turgid
Animal cells - lysis
osmosis out of the cell
Plant cells - flaccid
Animal cells - shrivel
Why do plant cells not burst when water enters cell by osmosis.
The cell wall is strong and withstands internal pressure.
The cell wall limits water uptake.
Define diffusion
Passive process.
The net movement of a particles down a concentration gradient.
Define facilitated diffusion
A passive process.
The net movement of particles down a concentration gradient.
Through specific intrinsic protein e.g. carrier/channel protein.
Explain how channel and carrier proteins work
Channel = hydrophilic channels bind to specific ions = one side of the protein closes and the other opens.
Carrier = binds to complementary molecule = change in shape releases molecule to other side.
Define active transport
An active process.
The movement of substances against a concentration gradient, using ATP and a transport protein.
Define exocytosis and endocytosis
Active processes which require ATP.
Vesicles fuse with cell surface membrane to transport particles.
Name five factors that affect the rate of diffusion
Temperature
Diffusion distance
Surface area
Size of molecule
Concentration gradient
