2.1.5 Biological Membranes Flashcards
what are the membranes like between the cell and its environment?
- partially permeable
- plasma membrane allows transfer of substances in and out of the cell
- e.g water, ions
what is the role of the membrane between organelles and cytoplasm?
- compartmentalisation
- in a lysozome, the hydrolytic enzymes need to be kept seperate from other organelles
- controls what enters and leaves organelle
what is the role of membranes within organelles?
- allows for concentration gradients to be created
- site of attatchment of enzymes into the membrane
what are the other roles of membranes inside a cell?
- sites of chemical reactions
- sites of cell communication
what happens in cell communication?
- communication between cells
- cell identification
- cells working together
- to trigger a response
why do phospholipids arrange themselves in a bilayer at the cell surface?
- hydrophilic heads orientate towards water and form hydrogen bonds
- hydrophobic tails orientate away from water
- water is present both outside and inside of the cell
what makes up a phospholipid bilayer in a fluid mosaic model?
- glycoproteins and glycolipids
- proteins
- cholesterol
- phospholipids
what is the function of glycolipids/glycoproteins?
- cell recognition
- cell signalling
- acts as antigens
- acts as receptors
- involved in cell adhesion (cells bind together)
what do carrier proteins do?
transports large and polar substances
what do channel proteins do?
transports polar substances
where is cholesterol found in the model and what does it do?
- found between the tails of the phospholipid
- it regulates fluidity of the membrane
- more cholesterol = less fluid
what factors affect membrane permeability?
- temperature
- solvent
what happens to permeability when you increase temperature?
- phospholipids gain kinetic energy
- causes gaps to appear between phospholipids
- membrane becomes more permeable
- at high temperatures, the proteins will denature
what happens to the permeability when temp decreases and water freezes?
- water expands and forms ice crystals
- break and pierce cell membrane making it more permeable
what is diffusion?
the net movement of molecules down a concentration gradient until equilibrium is reached