2.4.3~ the cell surface membrane Flashcards
phospholipd function
-form basic structure of the membrane
-act as a barrier to most water-soluble substances as the non-polar fatty acid chains prevent polar molecules or ions passing across the membrane
-ensures water soluble molecules such as sugars, amino acids and proteins cannot leak out the cell and unwanted water-soluble molecules cannot get in
how are phospholipids chemically modified to act as signalling molecules
-moving with the bilayer to activate other molecules
-being hydrolysed which releases smaller water-soluble molecules that bind to specific receptors in cytoplasm
what does cholesterol do
regulates fluidity of the membrane
cholesterol arrangement in bilayer
cholestrol molecules sit in between the phospholipds, preventing them from packing too closely together –> when temperatures are low this prevents membranes from freezing and fracturing
how does cholesterol stabilise membrane in high temperatures
stops membrane becoming too fluid as cholesterol molecules bind to hydrophobic tails of phosopholipds, stabilising them and causing phospholipds to pack more closely together
how does cholesterol prevent membrane from bursting
contributes to impermeability of the membrane to ions and increases mechanical strength and stability of membranes which without cells would break down and burst
what do glycolipids and glycoproteins act as
receptor molecules
where are the carbohydrate chains in the glycolipids and glycoproteins
on the surface (periphery/extrinsically)
what does glycolipids and glycoproteins acting as receptor molecules allow them to do
bind with certain substances at the cell’s surface
3 main receptor types
-signalling receptors for hormones and neurotransmitters
-receptors involved in endocytosis
-receptors involved in cell adhesion and stabilisation (as the carbohydrate part can form hydrogen bonds with water molecules surrounding the cell)
what do some glycolipids and glycoproteins act as
cell markers (antigens), for cell-to-cell recognition
what do transport proteins create
hydrophilic channels to allow ions and polar molecules to travel through the membrane
2 types of transport protein
-channel (pore) proteins
-carrier proteins
transport protein specificity
specific to a particular ion or molecule
what do transport proteins do
allow the cell to control which substances enter or leave
