Membrane Structure Flashcards
Where are hydrophobic tails in the cell membrane?
The middle
Where are polar head groups in the cell membrane?
The outside
How much of the membrane is proteins?
~50%
What is an amphiphilic molecule?
Has both hydrophobic and hydrophilic properties
What are polar head groups made of?
Choline, phosphate, glycerol at the top
What are hydrophobic tails of the lipid bilayer made of?
Fatty acids (unsaturated, saturated)
Difference between unsaturated and saturated?
Saturated = no double bonds Unsaturated = double bonds
Unsaturated less likely to freeze
How many common phospholipids are there?
Four
What’s different between the phospholipids?
Charge, tail length, what’s on the head
How many sections are there of the polar head and which is most charged?
3, they could all be charged
What is the purpose of cholesterol?
Stops hydrocarbon chains from freezing, makes membrane less permeable
How does cholesterol attach to lipids?
Polar head group of cholesterol lines up with lipids
What happens if there’s too much cholesterol?
Things can’t get in and out of the cell
Why can the membrane act as a fluid?
Lipids can rotate, diffuse, or flex (twist)
But they barely ever flip-flop
Is there the same amount of lipid in each cell membrane?
No, composition varies a ton depending on the membrane
How much cholesterol do bacteria have?
None
If you do in situ hybridization on a membrane, will the components be distributed randomly?
No, components of lipids are organized
What is a lipid raft?
Microdomain in membrane that concentrates membrane proteins
What are glycolipids useful for?
Attaching cells together
Can be charged (alter electrical field)
You fuse a mouse and human membrane together with mouse in one area. What happens?
Membrane proteins diffuse, and all the membrane proteins are intermixed
How do you measure protein diffusion?
FRAP
What does FRAP stand for?
Fluorescent recovery after photobleaching
How does FRAP work?
Destroy (bleach) area with laser > measure how long it takes to recover
How can membrane proteins interact with the membrane?
Interact with protein embedded in membrane
Go through membrane
Get stuck in membrane
What are integral membrane proteins?
They go through membrane
What are lipid-anchored proteins?
They bind to lipid molecules
What are lipid-anchored proteins?
They bind to lipid molecules
What do you need to see on a hydropathy plot to determine if a protein is an integral membrane protein?
Hydrophilic properties - many transmembrane domains
Is + or - on a hydropathy plot hydrophilic?
+ (Going up)
What’s in an aquaporin?
2 alpha helices go halfway through lipid bilayer
What common domain does an integral membrane protein have?
Alpha helix, has hydrophilic amino acids which go through hydrophobic core
What does ‘multipass’ in multipass transmembrane protein mean?
The protein passes through the membrane multiple times
What happens as a multipass transmembrane protein fold?
Lipid molecules get displaced as protein folds in closer to itself
What are porins?
Structures beta barrels create that let things through membrane
What does a beta barrel look like?
A bunch of beta sheets overlapping
What is the periplasm?
Space in between inner and outer membrane
Where are carbohydrates?
Coat the extracellular side of the cell membrane
What’s the function of the carbohydrate layer?
Protect it from mechanical forces, chemicals, etc
Cell recognition
What’s the function of the carbohydrate layer?
Protect it from mechanical forces, chemicals, etc
Cell recognition
What are detergents?
Small amphiphilic molecules
What are micelles?
Heteromeric vesicle-like structures that detergents form
Why use detergents to study membrane proteins?
Detergents grab proteins, mess with the lipid bilayer, and bring the proteins into solution
How would you study a Na+/K+ pump?
Solubilize membrane proteins with detergent
Remove detergent
Make your own membrane outside of the cell
What properties does a detergent need to be to grab a transmembrane protein without hurting it?
Nonionic, mild
How were ATP synthases first studied?
Using mild detergents to bring them out of membrane
How many domains do sperm cells have? why relevant?
- Shows there are distinct domains with distinct proteins
What (generally) laterally immobilizes membrane proteins?
Protein-protein interactions (e.g. stick them there)
interactions with other cells,
What types of molecules get across the membrane easily?
e.g. CO2, O2, N2 (hydrophobic molecules)
How easily can water get across?
Kinda
Can glucose/sucrose get across easily?
No, but a few do
Can ions get through a cell membrane?
absolutely not
What generally guides how easily a molecule crosses a membrane?
hydrophilicity
How do membrane-impermeable molecules get across a membrane?
Solute transporter proteins
What is the difference between transporter vs channel proteins?
Transporter = impermeable molecules bind, then they change conformation
Channel = they’re just tunnels for impermable molecules
What sources of energy can drive active transport?
ATP, light, coupled molecules
What’s a coupled transporter?
e.g. 3na+ with 2 K+
What’s a uniporter?
One molecule goes through one direction
What’s a symporter? (coupled transport)
A molecule and co-transported ion go through membrane the same way
What’s an antiporter? (coupled transport)
Two molecules go through membrane the opposite way
Take-home message for transport proteins?
They can be asymmetrically distributed in the membrane to cause specific planned movement
