2.1.5 Biological Membranes COMPLETE Flashcards
Roles of the Cell surface membrane
- Barrier to operate cell contents
- Controls movement in and out the cell
- Selective permeability
- Cell Recognition
- Attachment of multiple cells forms tissue
- Cell signalling e.g. the receptor site for hormones
Roles fo internal membranes
- Compartmentalisation
- Isolate Enzymes
- Control Entry and exit
- Attachment of ribosomes ect.
- Isolate DNA
Phospholipids in the membrane
Gives the membrane fluidity
A barrier to large soluble molecules and ions
Allows lipid soluble molecules to pass through
Unsaturated fatty acids have kinks on tails which prevents close packing
Proteins in the membrane
Adds structural support
Used in transport i.e. channel proteins
Act as receptors
Helps cells adhere together
Cholesterol in the membrane
A barrier to stop prevent large water soluble molecules to pass through
Reduces the lateral movement of the phospholipids
Gives mechanical stability
Glycocalyx
Glycoproteins and Glycolipids Receptor sites for hormones Cell markers Act as antigens allowing the cell to recognise self Helps cells adhere together q
Effect of Temperature on Membranes
Increased temp= Increased kinetic energy
therefore membrane becomes more permeable as the phospholipid vibrate and move further apart.
Sometimes membrane breaks down
Effect of Organic Solvents on Membranes
Organic solvents are less polar than water so san dissolve lipids.
Ethanol dissolves lipids on the membrane so it breaks down. Thus becomes more permeable
Diffusion
A passive process which doesn’t require ATP
The net movement of molecules or ions from a. region of high concentration to a region of lower concentration
Factors affecting rate of diffusion
Temperature Ion Size SA Concentration gradient Stirring/ moving Distance
Facilitated Diffusion
Either Channel Proteins for certain ions, i.e. Ca2+ which have a hydrophilic lining
or Carrier Proteins for large polar molecules, glucose binds to the protein so it changes shape and the molecule moves across the membrane
Osmosis
The net movement of water from a high water potential to a region of lower water potential down the gradient across a partially permeable membrane
DEFINITION- Solute
The substance that dissolves in a liquid to form a solution
DEFINITION- Solvent
The liquid in which a solute dissolves in
DEFINITION- Solution
The mixture formed when a solute has dissolved in a solvent
