lecture 21 - structure and function of the cell membrane Flashcards
(46 cards)
thickness of membrane
8nm
lipid bilayer structure described as? constitutes?
fluid mosaic. 50% lipids, 50% proteins (“floating in lipid sea”)
what holds proteins and lipids together?
hydrogen bonds
3 types of lipids in the bilayer
cholesterol and glycolipids scattered amongst double layer phospholipids (75%)
amphipathic
phospholipids have both a polar and a non-polar region
tails of phospholipids form?
hydrophobic core
lipids can move around in their respective __________ _________
membrane leaflet
do lipids flip flop between leaflets or nah?
very rarely (basically no) this allows leaflets to be assymetric in what they constitute.
longer lipid tail length =
less fluid membrane
more double bonds =
more fluid membrane (more space between lipids)
more cholesterol =
less fluid membrane
integral proteins
extend INTO or completely ACROSS the membrane (transmembrane protein)
peripheral proteins
associated with but NOT EMBEDDED into the membrane. Only on the surface. may be bonded to integral proteins. e.g. cytoskeleton proteins
how do integral membranes stay anchored in membrane?
hydrophobic regions span the hydrophobic core (non-polar amino acids coiled into alpha helices). the hydrophilic regions interact with the aqueous solution.
how is the maintenance of concentration gradients allowed?
by the cell membrane controlling what comes in and what doesn’t
functions of membrane proteins?
- receptors
- cell identity markers
- linkers
- enzymes
- channels
- transporters
organisation of of molecules in the membrane determines?
selective permeability
3 things lipid bilayer permeable to (alone)…
- non-polar, uncharged molecules (e.g. oxygen, nitrogen, benzene)
- lipid soluble molecules (e.g. steroids, vitamins)
- small, uncharged polar molecules (e.g. water, urea)
2 things lipid bilayer impermeable too… (due to hydrophobic core
- large uncharged polar molecules (e.g. glucose)
- Ions Na+, K+, Cl-, Ca2+, H+
diffusion
high to low areas of concentration. down concentration gradient. due to particles KE
ways to decrease rate of diffusion
lower temperature, larger molecule, smaller concentration difference, less surface area, larger distance
rate of diffusion limits cell size to…
20μm
how is O2 gradient maintained?
used up as quickly as it is provided
movement of ions influenced by…
electrochemical gradient = both concentration gradient and electrical gradient together
