Membrane Structure and Function Flashcards
What 3 components make up biological membrane?
lipids, proteins and carbohydrates
how are lipids arranged in biological membranes?
lipid bilayer
What’s the fluid mosaic model?
model of the lipid bilayer, emphasises fluidity with few proteins floating around
what does the evolved fluid mosaic model emphasise?
ordarrrrrrr
what determines the fluidity of the membrane?
composition of lipid chains determines fluidity of membrane
what’s more fluid long or short fatty acid chains?
short
what forms kinks in fatty acid chains?
cis-bonds
what do kinks in fatty acid chains do?
mean chains can’t pack so closely together, therefore increases fluidity
are cis bonds natural in fatty acids?
yes
are trans bonds natural in fatty acids?
no
when classifying membrane lipids by head groups, what are the 3 types?
phospholipids
glycolipids
cholesterol
how are lipids distributed in the bilayer?
asymmetrically
what generates the lipid asymmetry?
flippase
what is flippase?
an ATP pump/ ATPase
what is the outer-leaflet of the membrane?
the part on the extracellular side- (cell-cell contact)
what does the outer leaflet usually contain (3)?
PC (phosphotidylcholine), SM (sphingomyelin) (these are phospholipids) Glycolipids
what is the inner-leaflet of the membrane?
on the intracellular side (contact with cytoplasm- involved in signalling in cell)
what does the inner leaflet contain?
PE (phosphotidylethanolamine), PI (phosphotidylinositol) and PS (phosphotidylserine)- all phospholipids
what causes the loss of lipid asymmetry?
inhibition of flippases
or
acctivation of scramblases
what does loss of assymetry do?
affects cellular signals e.g. PS on outer leaflet would cause phagocytosis of cell
what’s the function of phospholipid in membrane lipid?
signaling and structure
what’s the function of cholesterol in membrane?
increases stability and reduces permeability
what’s the function of glycolipid in membrane?
cell recognition and protection
what’s the ratio by number of lipid molecules to proteins?
50:1
what’s the mass percentage of proteins in lipid membrane?
30-45%
what are the 3 functions of membrane protein?
structure
biochemical reactions
signaling/communication
what are the 2 main classes of membrane protein?
integral and peripheral
what are the 2 classes of integral protein?
transmembrane and anchored
what are the 2 types of transmembrane protein?
single pass
multi-pass
what are the 3 types of anchored protein?
embedded
GPI factor
lipid chain
what does the GPI protein do?
anchors protein to outer leaflet of plasma membrane
what are lipid chain anchored proteins used by?
kinases- involved in growth/division of cell
what 2 regions do transmembrane proteins have?
polar region
non-polar region
where are membrane lipids synthesised?
ER
how do membrane lipids get from the ER to the plasma membrane?
trafficked in membrane vesicles which fuse into the plasma membrane
where are membrane proteins synthesised?
rER
what does SRP stain for?
Signal Recognition particle
what does the SRP do?
signals the protein to the membrane and allows the protein to travel through the membrane
what sequences do transmembrane proteins have?
start- transfer and stop-transfer sequences- for single and multi-pass proteins
In what 3 ways are plasma proteins dynamic?
- can spin about a z-axis
- can change shape
- move laterally
what are lipid rafts?
tightly-packed lipids with ore cholesterol and saturated fatty acid chains, specific proteins
why are lipid rafts important?
protein trafficking to membrane, endocytosis, exocytosis, signalling complexes
diseases can target lipid rafts e.g. prions
what sort of permeability do lipids and gases have to membranes?
v. high
what sort of permeability does water have to membranes?
moderate
what sort of permeability do glucose and amino acids have to membranes?
low
what sort of permeability do ions have to membranes ?
none (need proteins)
what is overton’s rule?
solubility of a substance in oil is proportional to its membrane permeability (this isn’t quite true)
what rate- concentration relationship is seen in simple diffusion?
linear
what rate-concentration relationship is seen in protein mediated ion transport?
hyperbolic- it’s saturatable
what’s the structure of transport proteins?
integral - membrane spanning
AAs in lipid bilayer are lipophilic
AAs in pore region are hydrophobic (charged AAs)
describe the structure of voltage-gated K+ ion channels
6 TM domains
mostly alpha-helix
H5 segment containing charged AAs- pore
what are the 3 classes of membrane transport protein?
- ion channels
- ion pumps
- Solute Carriers (SC)
what do ion channels do?
facilitated diffusion of ions through bilayer
what do ion pumps do?
transport 1 or more substrate(s) against the concentration gradient using enzymes (ATPase) to hydrolyse ATP to ADP. This is primary active transport
what are the 3 main types of ion pumps?
P-type
V- type
F- type
what are the P-type ion pump?
typical ion pumps e.g. Na+,K+ ATPase and flippase enzymes
what are F-type ion pumps?
pumps that drive ATP synthesis in mitochondria (respiration)
what are V- type ion pumps?
H+ pumps in cell organelles
what do solute carriers do?
transport 1+ substrates (at least 1 down gradient, some against)
are solute carriers diverse?
yes- drug target
2nd most diverse after GPCR
which 3 types of transport do SCs use?
facilitated diffusion
contransporter/ symporters
exchangers (antiports)
what 2 influences affect the elctrochemical gradient?
membrane potential
chemical gradient
how is the Electrochemical gradient calculated?
Vm (membrane potential)- Ex (equilibrium potential)
how is equilibrium potential calculated?
nernst equation
what does the nernst equation do?
converts a known chemical gradient to an unknown electrical gradient
does water permeablility in membranes work as expected?
no- it’s more permeable than expected (water is polar)q
what mediates water permeability?
aquaporins
what are aquaporins?
water channels
what is Aquaporin 4 linked to?
brain inflammation- KO mice show increased survival from stroke
