cell membrane Flashcards
what are the components of the cell membrane?
- phospholipids
- cholesterol
- proteins
- glycoproteins and glycolipids
describe structure of phospholipids
- one hydrophilic phosphate head and two hydrophobic hydrocarbon tails/chains
- tends to form stable bilayers in aqueous medium or micelles
what contributes to the fluidity of membrane?
phospholipids in the membrane are held tgt by weak hydrophobic interactions and van der Waals’ forces
weak interactions–> phospholipids and proteins able to drift laterally within plane of membrane
what’s the r/o btwn temperature and phospholipids’ activity
as temp decreases, phospholipids become less active, settling into a closely packed arrangement, drawn by vdw forces and become less fluid, membrane eventually solidifies
temp at which memb eventually solidies depend on:
- the ratio of saturated to unsaturated hydrocarbon chains
- high prop of phospholipids with unsaturated–> kinks at cc double bonds of unsaturated hc tails prevent close packing of the phospholipids
- phospholipids compositions alter in response to temp change e.g. autumn plants increase unsaturated in autumn to prevent memb from solidifying in winter
- the relative amount of cholesterol in the membrane
structure of cholesterol
- characteristic four-ring structure and largely hydrophobic
- amphipathic: hydrophilic hydroxyl group and hydrophobic ring structure
- hydroxyl group of cholesterol aligns with phosphate heads of phospholipids while remaining portion of it is tucked into the hydrophobic core of the memb
how does cholesterol regulate membrane fluidity
- prevent the membrane from being overly fluid at warmer temp (restrict phospholipids movement)
- fused-ring structure of cholesterol is rigid and stabilises the lipid layer through vdw interactions
- prevent memb from being overly firm at low temp (prevents close packing of phospholipids and hinders solidification/crystalisation of the bilayer)
why is membrane fluidity impt?
fluidity affects the PERMEABILITY of the membrane; ability to serve as a BARRIER: to transport membrane proteins to specific regions of membrane and carry out vital cellular activities
what proteins are found in the membrane
1) intrinsic/integral proteins
2) extrinsic/peripheral proteins
describe the structure of integral proteins
- protein is folded in the way such that there is exposed hydrophobic and hydrophilic regions
- hydrophilic regions mostly consists of amino acids with polar/charged R groups while hydrophobic regions consist of a.a. with non-polar R groups
inserted into the membrane such that the hydrophobic regions (1) lie in the hydrophobic core of the phospholipid bilayer and the (2) hydrophilic parts were exposed to the aqueous medium on both/either side of membrane
what is extracellular matrix
the substance in which the animal tissue cells are embedded and consist of protein and polysaccharides
what is the cytoskeleton?
a network of microtubules, microfilaments, intermediate filaments that branch throughout the cytoplasm and serves a variety of mechanical and transport functions
importance of cytoskeleton and extracellular matrix
attachment of proteins to cytoskeleton and extracellular matrix helps maintain cell shape and fix the location of some memb proteins
characteristics of glycoproteins and glycolipids
(carbohydrate components)
carbs in the membrane tend to be covalently bonded to either proteins or lipids to form glycoproteins or glycolipids respectively–> usually oligosaccharides
varies in diff species, indiv of same species and diff cells
- always found projecting out of cell into extracellular matrix
functions of glycoproteins and glycolipids
- cell-cell recognition
- cell receptors
