BIOLOGY Module 2: Section 5- Biological membranes

membrane functions: plasma membrane

-cell surface membrane
- partially permeable, control which substances enter and leave the cell (diffusion, osmosis, active transport)
- allow recognition by other body cells (immune system)
- cell signaling

membrane functions: membranes within cells

surround organelles, separating the cell into compartments
- containing hydrolysing enzymes (lysosome)
- form vesicles to transport substances within the cell
- contain pigments (chlorophyll)

phospholipids

- form the phospholipid bilayer
- hydrophilic head
-hydrophobic tails

- bilayer forms with heads facing outwards and tailos inside
- creates a hydrophobic center, doesn't allow water soluble substances (ions and polar molecules) to diffuse through
- fat-soluble substances dissolve in the bilayer and pass through

glycoprotein

- conjugated protein
- stabilise the membrane, form hydrogen bonds with surrounding water molecules
- cell to cell cohesion
- act as receptors in cell signalling
- antigens (self antigens and immune response)

ion channel protein

allow facillitated diffusion of ions and small polar molecules across the membrane

carrier proteins

transport larger molecules and charged particles across the membrane by active transport or facillitated diffusion

glycolipid

- stabalise the membrane, form hydrogen bonds to surrounding water molecules
- recptor
-antigens

cholesterol

- regulates cell membrane fluidity
- bind to the hydrophobic tails of the phospholipids, causing them to pack closer together
- makes the membrane more rigid
- also has hydrophobic regions, create a further barrier to polar substances

factors affecting membrane permeability: solvents

- alcohols dissolve the lipid in the cell membranes
- increasing the concentration of the alcohol will increase membrane permeability

factors affecting membrane permeability: temperature