Lecture 17- Membranes and Membrane Proteins Flashcards
Membrane dynamic State?
- Below Tm (<– ?)
- Noncovalent interactions lock lipids into a semisolid gel phase
- Motion of individual lipids is limited
Liquid-ordered state (Lo)
Tm: Melting Temperature- switch/transition bw ordered & disordered state
Membrane Dynamic State?
- Above Tm
- Lipids are fluid w/ rapid motion in the plane of the membrane
- More motion w/in lipid interior
Liquid-disordered state (Ld)
Why is lipid membrane composition regulated and how?
To keep the transition/Tm BELOW the body temp of the organism
Why must the lipid composition of membranes adjust?
To maintain membrane fluidity (Remember: Tm is transition state bw Lo and Ld)
___________ fatty acids (FA) = high Tm
___________ FA = decreased Tm
Saturated FA = high Tm
Mixture of saturated & unsaturated FA = decreased Tm
Fluidity is affected by?
- ?
- ?
- ?
Fluidity is affected by?
- Temperature
- FA content
- Sterol Content
What is the process that maintains the same membrane fluidity even when external temp changes?
Bacterial Adaptation
What maintains membrane fluidity over a broader range of lipid composition?
Cholesterol
Cholesterol interacts w/ phospholipids w/ unsaturated fatty acyl chains that have a ______ Tm which will _______ the Tm and cause them to _______ to drive them to a more ________ state.
Cholesterol interacts w/ phospholipids w/ unsaturated fatty acyl chains that have a lower Tm which will increase the Tm and cause them to compact to drive them to a more ordered state.
Cholesterol interacts w/ phospholipids w/ saturated fatty acyl chains that have a ______ Tm will _______ the Tm and cause them to become more _______ to drive them to a more ________ state.
Cholesterol interacts w/ phospholipids w/ saturated fatty acyl chains that have a higher Tm which will decrease the Tm and cause them to become more fluid to drive them to a more disordered state.
Lipid Movement in the Bilayer:
- Lateral diffusion in the _____ of the bilayer occurs very rapidly
Lateral diffusion in the plane of the bilayer occurs very rapidly
Lipid Movement in the Bilayer:
- ___________ movement req’s a charged _____ group to leave the _________ environment and move into the ___________ interior of the bilayer
- What type of change is required for movement to proceed?
- Transbilayer movement req’s a charged head group to leave the aqueous environment and move into the hydrophobic interior of the bilayer
- Large (+) free energy change input required
Asymmetric distribution of lipids predicts the existence of enzymes that catalyze ____-____ _________.
Asymmetric distribution of lipids predicts the existence of enzymes that catalyze flip-flop diffusion.
What regulates lipid movement between leaflets?
Membrane Proteins
What type of catalyzed transbilayer translocation occurs w/ ATP and involves the movement of a lipid from the outer leaflet to the cytosilic interior leaflet?
Flippase
What type of catalyzed transbilayer translocation occurs w/ ATP and involves the movement of a phospholipids from the cytosilic interior leaflet to the outer leaflet?
Floppase
What type of catalyzed transbilayer translocation is an exchange that moves a lipid from the outer leaflet to the inner leaflet and a lipid from the inner leaflet to the outer leaflet towards equilibrium?
Scramblase
What are membrane microdomains enriched w/ cholesterol and sphingolipids in the outer leaflet?
Microdomains are slightly thicker and have a more ___ state.
Lipid Rafts
Lo
What are lipid rafts rich in and where does the cholesterol fill up? (2 locations)
GPI proteins
- Under the head group of sphingolipids
- Crowds around the fatty acyl chains in the apposing leaflet
What requires changes in membrane curvature and results in the fusion of 2 membranes without losing membrane continuity?
Membrane reorganization
Membrane Fusion during NT Release at a Synapse:
- ________ ________ loaded w/ __, approaches plasma membrane
- _& _-snares bind to ____ _____, zip up into ______ from ______ terminal
- ________ & _________ bilayers draw together and _______ initiates
- Complete fusion results in ___ released into ________ cleft.
Membrane Fusion during NT Release at a Synapse:
- Synaptic vesicle loaded w/ NT, approaches plasma membrane
- V& T-snares bind to each other, zip up into helices from amino terminal
- Vesicle & membrane bilayers draw together and fusion initiates
- Complete fusion results in NT released into synaptic cleft.
Transport across intact membranes:
- ________ ________ leads to electro-chemical gradient.
- A few ________ compounds (__,___) can dissolve in the lipid bilayer and cross the membrane unassisted.
- For transmembrane transport of any _____ compound/ion a _______ _______ is reqd.
- Direction of transport determined by?
- Transport against a gradient requires? (2)
- Happens spontaneously (?) or gated (? ?)
Transport across intact membranes:
- Membrane barrier leads to electro-chemical gradient.
- A few nonpolar compounds (O2,CO2) can dissolve in the lipid bilayer and cross the membrane unassisted.
- For transmembrane transport of any polar compound/ion a membrane protein is reqd.
- Direction of transport determined by electrochemical gradient for diffusion.
- Transport against a gradient requires either energy or ion exchange down a gradient (active transport)
- Happens spontaneously (porins) or gated (ion channels)
Chemical Gradients
- Net movement of an electrically ______ solute is toward the side of _______ concentration.
- Rate of movement is __________ to concentration ratio (C2/C1)
- Net movement of an electrically neutral solute is toward the side of lower concentration.
- Rate of movement is proportional to concentration ratio (C2/C1)
Electrochemical Gradients
- Net movement of an electrically _______ solute is dictated by a combo of 1.) The _______ gradient or membrane _________ (Vm) and 2.) The _____ of the chemical concentrations (C2/C1)
- Ions will move ______ the membrane until the electrochemical potential reaches _____
- Net movement of an electrically charged solute is dictated by a combo of 1.) The electrical gradient or membrane potential (Vm) and 2.) The ratio of the chemical concentrations (C2/C1)
- Ions will move across the membrane until the electrochemical potential reaches zero
Energetics of Transport Across Membranes
- _______ lower the barrier (energy of activation for diffusion)
- _______ of water (________ ______)- protein forms ___________ interactions w/ dehydrated solute to replace __-bonding with ______
- Movement thru opening in _______
- Barrier bw ______ and __________ lipids
- ________ & ________: membrane proteins that speed the movement of a solute across a membrane by facilitating diffusion
- Proteins lower the barrier (energy of activation for diffusion)
- Removal of water (Hydration shell)- protein forms noncovalent interactions w/ dehydrated solute to replace H-bonding with water
- Movement thru opening in protein
- Barrier bw solute and hydrophobic lipids
- Transporters & Channels: membrane proteins that speed the movement of a solute across a membrane by facilitating diffusion
Transmembrane Transport: Channel
- Allow transmembrane transport approaching?
- Pump functioning and # of gates?
- Saturable?
Transmembrane Transport: Channel
- Allow transmembrane transport approaching the limit of free diffusion
- Pump functioning? NO, single gate
- Saturable? NO, doesn’t obey saturation kinetics
Transmembrane Transport: Transporters
- Bind substarates with?
- Transport at rates…?
- Pump functioning and # gates?
- Saturable?
- Bind substarates with high specificity
- Transport at rates below that limits of free diffusion
- Pump functioning? YES, can move a substrate against a gradient (alternating gates)
- Saturable? Yes, obeys saturation kinetics
