The cell membrane Flashcards
compartmentalisation
Allows for life
only happened due to plasma membranes
Amphipatic lipids
amiphipathic- molecule consisting of a hydrophobic and hydrophilic part
phospholipids are an example of this
structure polar head and fatty acid tail
hydrophillic head and hydrophobic tail
Amphipatic lipids hydrophobic collapse
fatty acid of different lipids interact throu hydrophobic collapse the polar head would allow this to take place in water
micelles - one layer of amphipatic lipids
lipid bilayer- two layer
liposome- cicular shape with a lipid bilayer
Biological membrane
bilayers define boundaries of cell from outer boundary and internal cell compartment
semipermeable and selective - depend on size of molecule /receptor/gradient
- fluidic -not rigid and allows mobility
phospholipid monolayer vs bilayer
in monolayer means inside is completely hydrophobic and water cant enter and also are smaller in size.
in bilayer it can due to the heads facing inwards and outwards
lipid composition
varies among biological membranes
main ones cholestrol, glycolipids, phosphatidylserine
phospolipids structure
mainly a glycerol backbone, phosphate group and two fatty acid chains
glycerol derivatives- phosphatidylethanolamine
phosphatidylserine - net negative
phosphatidylcholine
sphingosine derivatine- sphingomyelin
all polar
Cholesterol
in eukaryotic cells not bacteria
smaller than other phospholipids
smaller head and rigid steroid ring structure and nonpolar hydrocarbon tail
glycolipids structure
not major component of mambrane
have a carbohydrate structure on head
galactocerebroside- have galactose bound to head
in inner membrane
phospholipids are present in small quantities in the inner membrane PIP2 will be phophorylated by PI3K to PIP3 and back by PTEN
membrane fluidity
lateral diffusionm of components
rapid in phospholipids
and transverse diffusion is very slow
regulation of membrane fluidity
length and saturation of hydrocarbon tails affects fluidity
longer and higher saturation = less fluidity
temp also increase fluidity
cholesterol content involved but complicated - at warm cholesterol decreases it and at cooler temp in maintains fluidity
distribution of lipids in inner and outer layer of membrane
distribution is asymetric
phosphatidylserine and phosphatidylethanolamine are more present in inner - serine creates signalling hubs due to negative charge for proteis such as kinase C
and phosphatidylcholine and sphingomyelin are outter
flip flop movement
when cells under go apoptosis membrane is depolarised and thus phospholipids inside are now out side and attracts immune cells.
intracellular signalling
conc of PIP2 and PIP3 induces and regulate this
how does the cell maintain fluidity under increase in temp
incorparate larger amounts of saturated fatty acids and decrease non saturated
how do cells react to hyperthermia
increases migration of cells
WIP is involved in detection of change of temp in immune cells
changes in lipid composition occurs more in wild type then the ones that dont have wip
Proteins
trans membrane proteins extend across the bilayer and have either a single alpha helix or multiple helixes or as a rolled up beta sheet and also may include some gobular domains. may also be single or multipass with a fatty acid chain inserted in the cytosolic lipid monolayer
functions of membrane proteins
trandporters of ions and small molecules
cell adhesion molecules; cell-cell contact,cell-extracellular matrix contact
receptors for soluble factors; gormone receprors, cytokine receptors
proteins specific for organelle function; electron transport chain and ATp synthase
Electrical properties of biological membrane
membrane potential ; voltage across the cell membrane caused by electric charge difference inside and outside due to passive diffusion and pumping by ion channels
ions such as k+,Na+,H+
formation of functional domains
planar aggregation - free proteins in lipid layers interact with each other and when interaction is stablised form aggregates
also works with lipids and creates areas with enrichment and exclusion of certain types of lipids
sequestration- areas will favour a more organised protein distrbution and can cause exclusion
extracellular environment could also favour a certain type of interaction and thus effect the proteins in the domain
cytoskeleton - can interqact with certain proteins and also favour them and thus have an effect on protein localisation
proteins form functional regions by ?
binding of extracellular domains to the extracellular matrix and/or receptors of neighbouring cells or other proteins within the cell membrane
binding of cytoplasmic domains to cytoplasmic proteins or the cytoskeleton
interaction with lipids; lipid rafts
lipid rafts
small specialized discrete areas in membranes rich primarily in sphingolipids and cholesterol where some proteins are concentrated
functional polarisation
organisation of domains with different functions
segregation of proteins and lipids by
formation of lipid raft and nano domains
binding of proteins to neighbouring cells
binding of proteins to cytoskeletal points
