Pintar - Cell Membrane

Question 1

Phosphoglyceride

Answer 1

polar head group with both a + charge from the group on top and a - charge from the phosphate group is attached to a glycerol (3 hydroxyls) which is then attached to 2 fatty acid tails. One tail with a double bond that causes a a kink and it to be unsaturated
- very important because if there were two straight chains then at physiological temps they would freeze.

Question 2

Main types of phosphoglyceride

Answer 2

phosphotidyl ethanolamine
phosphotidyl serine (Net negative)
phosphotidyl choline
sphingomyelin (sphingosine is progenitor and has an N group in it)

Question 3

Other things found in cell membrane

Answer 3

Cholesterol - Polar molecule with ring structure. Provides stiffness to the cell membrane. Can sit on the inside or outside of the PM. The polar side of cholesterol can sit on the outside and interact with water. The aliphatic part can sit on the inner leaflet and interact with the lipids.

lycolipids - Also have fatty acid chains, but instead of a phosphate they have a sugar on top. Sugars can be charged. Derived from sphingosine.

Question 4

Bacteria have no cholesterol so how do they maintain their cell structure?

Answer 4

Cell wall

Question 5

Lipid movement

Answer 5

Lipids can move laterally pretty often

Lipids can also flip-flop on occasion from one leaf to the other leaf

Question 6

Lipid asymmetry across membrane

Answer 6

The inner side of the membrane is negatively charged, why? Because on the inside of the membrane we have phosphotidylserine, which has a net negative charge as well as phosphotidylethanolamine.
On the outside layer we have phosphotidylcholine, sphingolipids, and glycolipids

Question 7

Lipid asymmetry - lipid rafts

Answer 7

Lipid rafts are areas within the membrane where there is asymmetry in that there are many sphingomysin and cholsterol congregating on the outer leaflet of the membrane. This causes that part of the membrane to be thicker and begin to look a little like a raft. This can then recruit other membrane proteins to this area.

Question 8

Membrane Proteins

• types?
• are they altered?

Answer 8

Integral that have a polar part sticking out and a NP spanning the membrane
Integral that have lipid covalently attached so that they can reversibly interact with the membrane
Peripheral which usually associate with t he membrane via charge

They can be post-translationally altered with lipids so that they can interact easily with the membranes.

Question 9

Channels

- also things that mess with channel activity

Answer 9

Not so selective
Super fast (10^6)
Allows many ions to go down their conc gradient very rapidly
Doesn't need energy

• tetrodotoxin from pufferfish as well as lidocaine block sodium channels
• scorpions and some snails block potassium
• Curare is acetylcholine channel blocker

Question 10

Carrier

- 3 kinds

Answer 10

Somewhat specific
Not as fast as a channel
It goes down the concentration gradient
You can pull another solute up the conc gradient with this mechanism
Doesn't need energy

uniporter - takes one molecule on one side and spits it out onto the other side
symporter - One molecule will bind that is going down the conc gradient as well as another molecule that is going up it’s conc gradient
antiporter - dont worry about

Question 11

Pump

Answer 11

Very slow
Goes up conc gradient
Needs energy

Question 12

What can and can’t cross a membrane without help?

Answer 12

Hydrophobic molecules and gasses can very easily
Small uncharged polar molecules can a little and slowly
Large uncharged polar molecules very very slowly
Ions can’t

Question 13

Uniporter carrier

Answer 13

Oscillates between being open to outside and being open on the inside. The rate at which solutes go is dependent on substrate binding to the inside of the channel as well as the concentration gradient.

Question 14

Symport carrier

Answer 14

Binding of Na+ will increase the affinity of the transporter for glucose. Once they are both bound it will cause a conformational change to occur. No energy expenditure.
Is found in epithelial cells by the microvilli. Once this happens, Glucose can use a uniporter to go down it’s conc gradient into the extracellular fluid. However, when this happens the inside of the cell becomes saturated with Na+, so what happens? There is a Na+/K+ pump that forces Na+ into the extracellular fluid and K+ into the cell.

Question 15

Types of pumps: P-type pump

- Examples

Answer 15

kinases that phosphoryate themselves which causes a conformational change. Needs ATP. Pumps ions.
- Used in the Sarcoplasmic reticulum. 90% of membrane proteins in this membrane are Ca2+ATPase, which put Ca2+ into the membrane space. They can bind ATP, have kinase domain, and have a specific AA that has been identified that can be phosphorylated. Once the phosphorylation occurs, there is a conformational change that causes Ca2+ to enter the sarcoplasmic reticulum from the cytoplasm.

• Na+/K+ transporter. 3 Na+ enter pump. ATP is hydrolyzed to ADP. Na+ are released and 2 K+ enter pump. Both are pumped against their conc gradient.

Question 16

Types of pumps: ABC transporter

- example

Answer 16

transports small molecules rather than ions. Needs ATP. You have ATPase binding domains on one side of the membrane (can be two). In the state where ATP is not bound, small molecules can bind the pump. When ATP binds there is a conformational change which causes the pump to expose the substrate to the other side of the membrane. Once ATP is hydrolyzed to ADP, there is release of the solute on the other side of the membrane.

• multiple drug resistance - the cancer cells will cause the ATP transporters to work at a very high level in response to the drug treatment. So instead of the drugs killing the cell, it is actually helping keep it alive.
• Chloriquine - same as ccancer treatment above
• CFTR is a type of ABC pump

Question 17

4 classes of membrane lipids:

Answer 17

Phosphoglycerides
Sphingolipids
Glycolipids
Sterols