Chapter 9- Lipid Membranes Flashcards
Lipids ____ in water due to ____
aggregate
hydrophobic interactions
Lipids aggregate can form:
- Micelles
- Bilayers
- Vesicles
Single tailed amphiphiles form ____ because of their ______
spheroidal or ellipsoidal micelles
conical shapes
Amphiphile monomers do not form micelles until they surpass a ______
certain concentration
Critical micelle concentration (CMC) definition
concentration above which micelles form
Above CMC =
Below CMC=
mostly monomers
mostly micelles
CMC is a measure of the strength of _____
amphiphile association
Low CMC means
strong association (micelle forms at low concentration)
High CMC means
weak association (micelle forms at high concentration)
Lipid Properties Influencing CMC
- Charge
- Aliphatic chain length
- unsaturation
- ionic strength
How does charge affect CMC
charge raises CMC because electrostatic repulsion requires a higher concentration to overcome
How does chain length affect CMC?
the longer the chain, the lower the CMC (association more favorable)
How does unsaturation affect double bonds?
more double bonds mean higher CMC (more difficult to associate)
How does ionic strength affect CMC?
higher ionic strength means a lower CMC
Which lipids tend to form bilayers?
Sphingolipids and glycerophospholipids (due to their cylindrical shape)
the thickness of the lipid bilayer tails and heads? overall?
~15 A
~60 A
Membranes can form different fluidity phases like:
solid- ordered
liquid-disordered
Solid-ordered lipid bilayer characteristics:
- straight rigid acyl chains
- proteins + lipids fixed in place
Liquid-disordered lipid bilayer characteristics:
- wiggling disorderly acyl chains
- proteins and lipids move
- typical for unsaturated acyl chains
The temperature required to induce the liquid-disordered phase is:
phase transition temp
Unsaturated and short chains make membranes more ____ at lower temp
fluid
Liquid ordered phase is induced by ____ and is a hybrid of ___
cholesterol
liquid disordered and solid phases
liquid-ordered phase characteristics
- straight acyl chains
- proteins and lipids move
- much of plasma membrane is like this
Role cholesterol plays in membranes
- maintain bilayer in fluid-like state
- needed for biological functions
Cholesterol _____ fluidity under the Tm and ______ fluidity over the Tm
increases
decreases
types of Lipid bilayer dynamics
- lateral diffusion
- transverse diffusion
Lateral diffusion is a very ____ process
fast
What is lateral diffusion?
a lipid moves across the bilayer
how can the rate of lateral diffusion be determined experimentally?
single particle tracking of labeled lipids
Transverse diffusion is an extremely ____ event
rare
What is transverse diffusion?
transfer of lipids across the bilayer
Why is transverse diffusion unfavorable?
polar head must diffuse through the hydrocarbon core
Transverse diffusion is a very ____ process
slow
The extracellular leaflet has an overall ____ charge
neutral
the extracellular leaflet is enriched in
- Sphingomyelin and phosphatidylcholine
- glycolipids in the outer leaflet
The cytosolic leaflet is enriched in:
more negative charges present
Bilayer permeability depends partly on ___ but mostly on ____
size
hydrophobicity
____ and ____ molecules diffuse across the lipid bilayer
small
hydrophobic
Lipid bilayers of highly impermeable to ____ molecules
charged
Transport proteins lower ______ of molecules crossing the bilayer
activation energy
Polar molecules have _____ when crossing the membrane
extremely high energy of activation
Transporter proteins can facilitate ____ across the membrane
facilitate
Types of membrane proteins
- integral membrane proteins
- peripheral membrane proteins
Integral membrane proteins reside ____
in the membrane
Peripheral membrane proteins are found ____
attached to the membrane through a covalently attached lipid chain
Since integral proteins reside within the bilayer they are:
- hydrophobic
- insoluble in aqueous buffer
- need detergents to be solubilized
Residues found in transmembrane domains:
V, M. F, I, and L
transmembrane domains often form ___
alpha helices
How many residues span the hydrophobic core of a transmembrane domain
~20
How can helical transmembrane domains be predicted?
hydropathy plot for protein of interest
Beta barrel membrane protein characteristics
- every other residue interacts with lipids
- only 7-9 residues span the hydrophobic core
Peripheral membrane proteins are typically water ____
soluble
Peripheral membrane proteins are associated through:
- electrostatic interactions
- H-bonding
Association of peripheral membrane proteins is generally ____ and is often ____
reversible
regulated
peripheral membrane proteins can associate through ___ helix which has:
an amphipathic
1 hydrophobic face and 1 polar face
attachment of lipid ____ can alter the properties and localization of proteins
moieties
