[4.1] structure of the cell-surface membrane Flashcards
key feature of the phospholipid bilayer (8)
- hydrophilic head
- hydrophobic tails
- cholesterol
- glycolipids
- glycoproteins
- channel proteins (transmembrane protein)
- carrier proteins
- extrinsic proteins
what are the functions of the phospholipid bilayer?
- acts as a barrier for many substances
- maintains the shape of the cell and its internal environment
- plays a vital role in cell recognition and communication
- forms the boundary between the cell cytoplasm and the environment
- allows different conditions to be established inside and outside of a cell
- controls the movement of substances in and out of the cell
describe the structure of a phospholipid
glycerol attached to 2 fatty acid chains and an inorganic phosphate group (google it xoxo)
describe the heads and tails’ relationship with water
- hydrophilic heads point to the outside of the cell-surface membrane as they are attracted to water
- hydrophobic tails point to the centre of the cell-surface membrane as they are repelled by water
what are examples of aqueous environments hydrophobic fatty acid tails will be repelled by? (7)
- water
- blood plasma
- cell sap
- tissue fluid
- cytoplasm
- matrix (mitochondria)
- stroma (chloroplast)
what is the function of channel proteins?
water-filled tubes to allow water-soluble ions to diffuse across the membrane
what is the function of carrier proteins?
bind to ions or molecules eg. glucose & AAs, then changes shape so they can move across the membrane
what is the function of extrinsic proteins?
- give mechanical support to the membrane
- in conjunction with glycolipids, they act as cell receptors for molecules such as hormones
what are general functions of the proteins in the membrane?
- provide structural support
- act as channel transporting water-soluble substances across the membrane
- allow active transport across the membrane through carrier proteins
- form cell-surface receptors for identifying cells
- helps cells adhere together
- act as receptors eg. hormones
what are the functions of cholesterol in the membrane?
- add strength
- prevent leakage of water and dissolved ions
- reduce lateral movement of other molecules including phospholipids by pulling together the tails, limiting their movement and that of other molecules
- make the membrane less fluid at high temperatures
what is a glycolipid made up of?
a carbohydrate covalently bonded with a lipid
what are the functions of glycolipids in the membrane?
- act as recognition sites
- help maintain the stability of the membrane
- helps cells to attach to one another and so form tissues
what are glycoproteins made of?
carbohydrate chains attached to many extrinsic proteins
what are the functions of glycoproteins?
- act as recognition sites
- helps cells to attach to one another and so form tissues
- allows cells to recognise one another eg. lymphocytes can recognise an organism’s own cells
what are the functions of membranes within cell?
- control entry and exit of materials in organelles eg. mitochondria, chloroplast
- separate organelles from cytoplasm so that specific metabolic reactions can take place within them
- provide an internal transport system eg. ER
- isolate enzymes that might damage the cell eg. lysosomes
- provide surfaces on which reactions can occur eg. protein synthesis using ribosomes on RER
