Membrane Transport and Structure Flashcards
Give 4 realistic features of the fluid mosaic model
- Crowded bilayer
- Patchwork appearance
- Local bilayer distortion
- Protein complexes
Why do lipids spontaneously self-associate?
The hydrophobic effect and van der Waals interactions between the fatty acid tails
What is one of the main components of many membranes?
Glycerophospholipids
Why is cholesterol important in membranes?
Modulates packing of lipids and fluidity of membrane
Give the 4 ways lipids can move in a membrane
- flip-flop from one side of membrane to the other
- lipids diffuse laterally (movement left or right in the same leaflet)
- rotate freely around their long axis
- hydrocarbon chains are flexible and dynamic so wobble
What is the transition temperature of a membrane?
The temperature at which bilayers change from a fluid to a rigid gel phase
What is the effect of shorter chains or double bonds in phospholipids on transition temperature?
It lowers it
How is lateral diffusion affected by membranes being in the gel phase?
It is greatly reduced
Name the 2 enzymes involved in the maintenance of membrane asymmetry
Flippase and floppase
Give an example of a lipid transported by flippase
Phosphatidylserine
What do flippase and floppase use as a source of energy?
ATP hydrolysis
Which direction does floppase move lipids?
From the inner to the outer leaflet (against conc. gradient)
Which direction does flippase move membrane lipids?
From outer to inner leaflet (against conc. gradient)
Give an example of a lipid moved by floppase
Sphingolipid
Are integral membrane proteins generally soluble in aqueous buffers?
No
What is the only way integral membrane proteins can be separated from membranes?
By using agents which disrupt membranes
Are peripheral membrane proteins often soluble in aqueous buffers?
Yes
How are peripheral membrane proteins bound?
To the surface only via binding to integral membrane proteins and/or directly with the lipid headgroup regions
What is the typical structure of integral membrane proteins?
- α-helical or ß-barrel
- Structured or unstructured loops outside the membrane
Which is the more common structure for integral membrane proteins?
α-helical
Where are ß-barrel integral membrane proteins found?
In bacterial outermembranes, mitochondria, and chloroplasts
What type of amino acids do integral membrane proteins contain a lot of?
Hydrophobic
What is the typical length of an α-helix?
20-25 amino acids
How can α-helices be predicted?
The prescence of a string of hydrophobic amino acids in the sequence
What types of amino acids are found in ß sheets?
Alternating polar and hydrophobic amino acids
Are all membranes asymmetric?
No but many are
What is the difference between a transporter and a channel?
A transporter transports molecules down/against a concentration gradient whereas a channel only allows for diffusion down a concentration gradient
What is the effect of increasing concentration of the transported molecule on rate of transport in channel proteins?
It increases proportionally to the increase in concentration
What is the effect of increasing concentration of the transported molecule on rate of transport in transporters?
It increases but plateaus off (follows Michaelis-Mensen kinetics)
Where do solute transporters get their energy to transport molecules against a concentration gradient from?
The movement of one solute from [high] to [low] aka cotransport
What are the 3 types of transporter?
- Uniport
- Symport
- Antiport
Describe the movement of a symport transporter
Describe the direction of an antiport transporter
The hydrolysis of 1ATP moves what in ATPase?
- 3Na+
- 2K+
How many Na+ are moved out of a cell for every 2k+ moved in?
3
How many K+ are moved in for every 3 Na+ moved out?
2
Briefly outline the structure of ATPase
The region of binding and hydrolysis of ATP is distinct from the region through which ions travel
What does the F in the Nerst equation represent?
The Faraday constant
Give an example of sodium transporters in health and disease
- Glucose uptake depends on Na+:glucose symporters
- These transporters promote te readsorption of glucose from the bloodstream
- Inhibitors of SGLTs can be used to treat diabetes
Give an example of a proton-coupled transporter
Lactose Permease
Why type of transporter is lactose permease?
Outline the movement of the molecules
Symport (H+ are moved from high to low conc. whilst lactose is moved from low to high)
What is the mechanism for LacY? (lactose permease)
- Never fully opens a pore (Sealed by a rocker-switch mechanism)
- Position of an H bond moves in order to allow for a conformational change in shape
Give the features of ABC transporters
- Use ATP binding and hydrolysis to directly power transport
- Both export and import substances
Give an example of ABC transporters in context of health and disease
- MDR1 is a transporter whose natural function is to protect cells from toxic compounds
- It is a problem as it pumps drugs out of a cell
- Involved in aquired multidrug resistance in cancer
How does light-activated transport work?
- Bacteriorhodopsin absorbs light at a certain wavelength
- Upon light activation, it moved H+ across the membrane and generates a proton motive force
