Lecture 7

Front 1

1. Describe a micelle.

2. Describe a bilayer.

3. Describe a liposome.

Back 1

1. A ball of hydrophobic chains and the outside hydrophilic heads. Made up of wedge shaped units (cross section of head greater than that of side chain)

2. A layer formed from phospholipid like molecules.

3. Similiar to micelle, except has bilayer instead of just heads facing out.

Front 2

1. When do micelles or bilayers form?

2. What happens if the pH > pKa? What forms if we are above the CMC threshold?

3. If the pH = pKa?

4. If the pH < pKa?

Back 2

1. When there is a critical concentration of them

2. Micelles will form. (primarily deprotonated)

3. Bilayers will form.

4. Oil/fat droplets will form.

Front 3

1. What happens during a phase transition of a cell membrane?

2. Is the transition narrow or wide for a full phospholipid bilayer?

3. Which takes up more room, the liquid phase or gel phase of a membrane?

Back 3

1. There is a change in conformation. If going from gel -> liquid, one goes from anti -> gauche.

2. Very narrow. As you add more proteins, or cholesterol, it broadens.

3. The liquid phase

Front 4

1. How does increasing fatty acid chain length affect the transition temperature?

2. How does increasing the amount of saturated fatty acids affect the transition temp?

3. How does adding cholesterol affect the transition peak?

Back 4

1. Increases transition temp

2. Increases it.

3. Broadens transition peak.

Front 5

1. What is the general structure of a phospholipid?

2. Which two phospholipids have very small head groups?

3. Which two have larger head groups?

Back 5

1. Has a glycerol backbone with two fatty acids and a very polar head group.

2. Phosphatidylethanolamine and phosphatidylserine.

3. Phosphatidylcholine and sphingomyelin.

Front 6

1. Do different membranes have different lipid compositions?

2. Can cholesterol form a bilayer?

3. What effect does cholesterol have on membranes?

Back 6

1. Yes.

2. Yes.

3. It packs in between phospholipids, making the head groups stiffer while making the membrane more fluid. Broadens the transition phase.

Front 7

1. How can lipids move in a membrane?

2. Does the structure of the outside of a membrane look the same as the inside?

Back 7

1. Laterally, flexion (flex their legs), rotation and sometimes flip-flop.

2. No, typically the outer leaflet has larger head groups while the inner has smaller.

Front 8

Say whether the following items are more likely to be found on the inside or outside membrane.

1. Phosphatidylcholine and sphingomyelin?
2. Glycolipids?
3. Cholesterol?
4. Phosphatidylethanolamine and phosphatidylserine?
5. Phosphatidylinositol?

Back 8

1. Outside

2. Outside

3. Inside and outside

4. Inside

5. Inside

Front 9

1. How are lipids synthesized?

2. So how do we explain lipid asymmetry?

Back 9

1. From the ER, where they go to the inside of the membrane.

2. Flippase (or other enzymes) can move phospholipids to the other bilayer

Front 10

1. What is an integral protein?

2. What is a hydropathy plot?

3. What can the hydropathy plot be used for?

Back 10

1. One that completely spans the membrane.

2. A plot that measures how hydrophobic or hydrophilic the amino acids of a protein chain are.

3. Predicting the membrane spanning regions of a protein (or whether the protein spans a membrane at all)

Front 11

1. How are peripheral membranes connected to the membrane?

2. Where is the protein GPI generally found?

Back 11

1. Non-covalently

2. Outside of the protein

Front 12

Can the following diffuse through the membrane?
1. Gases (CO2, N2 O2)
2. Small uncharged polar molecultes (Ethanol)
3. Water/Urea
4. Large uncharged polar molecules (Glucose)
5. Ions
6. Charged polar molecules (amino acids, ATP)

Back 12

1. Yes, easily.
2. Yes, easily.
3. Kind of. Slowly.
4. No
5. No
6. No

Front 13

1. What is the partition coefficient?

2. What does an increase in K equal?

Back 13

1. A measure of hydrophobicity. K = Cm / Caq (Cm = tendency of particle to be in the membrane vs Caq = tendency of particle to be in aqueous solution)

2. More efficiently moves across the membrane (increased hydrophobicity)

Front 14

1. What are the three types of main transports?

2. What is the difference between mediated versus nonmediated transport?

3. What does cotransport mean?

Back 14

1. Uniport, symport, antiport.

2. Mediated has a protein involved in the transport.

3. Means two particles are being transported at the same time

Front 15

1. What is the difference between facilitated diffusion versus simple diffusion?

2. What is active transport?

Back 15

1. Facilitated diffusion uses a protein (mediated) to help move large charged particles with their concentration gradient. No energy input into either.

2. Requires energy, against gradient, requires protein. Gets energy from ATP hydrolysis or chemical gradient.

Front 16

1. What are the two classes of transport proteins?

2. What are the two classes of carriers?

3. What is the difference between carriers versus channels?

Back 16

1. Channels versus carriers.

2. Transporters (with the gradient or coupled transport), or ATP powered pumps (against [] gradient).

3. Carriers bind with specificity, rates below limit of diffusion and saturable. Channels are nonsaturable, less specific and rates very high.

Front 17

1. Which is larger, Na+ or K+?

2. So how does K+ stay out of Na+ channels?

3. How does Na+ stay out of K+ channels?

Back 17

1. K+

2. K+ is too big.

3. The transport protein has some carbonyls that need to interact with the ion + water before the channel will open up. When Na+ binds with water, it is too tiny to reach the carbonyls and thus the ion doesn't get passed through.

Front 18

1. How does the glucose transporter work?

2. How is the Na+/K+ gradient across a cell membrane?

Back 18

1. Protein is open to one side. Glucose binds, and the protein changes configuration to open to the inside of the cell.

2. Na+ is found in blood (outside of cell) while K+ has a high [ ] in the cell.

Front 19

Describe a Na+/K+ ATPase.

Back 19

Tetramer with 2 alpha (ion movement) and 2 beta proteins (folding of alpha). 3 Na+ in, 2 K+ out of cell. Antiporter (both against gradients). Uses a lot of ATP (30% produced) or 75% in active neurons

Front 20

Describe the Na+/K+ ATPase cycle.

Back 20

3 Na+ bind along with ATP from the outside of the cell. Asp gets phosphorylated, which induces a conformational change. K+ binding results in Na+ release. Dephophorylation and conformational change which stimulates K+ release.

Front 21

1. What does the fluid mosaic model mean?

2. How did we get evidence for this?

Back 21

1. Proteins can fluidly move laterally in a membrane unless they are anchored somewhere.

2. The Frye-Edinin experiment. Labeled two difference antibodies with different florescence. and let them bind opposite sides of the cell. Then checked later to see whether the florescences were mixed.

Front 22

1. What is a lipid raft?

2. Which side of the membrane are glycoproteins or glycolipids always found?

Back 22

1. A raft that moves laterally together. Sort of bulges out and enriched in sphingolipids or cholesterol.

2. On the outside of the membrane

Front 23

What is FRAP?

Back 23

Florescent Recovery After Photobleaching. Whole cell is florescent, but use a laser to bleach one spot. Watch to see how long it takes to recover florescence. The faster it recovers, the more lateral diffusion of the membrane. If it doesn't recover, then proteins are highly anchored.

Front 24

1. What is signal transduction?

2. What are three parts of a generalized signaling pathways?

Back 24

1. Has binding specific for a ligand and elicits a discrete response upon binding. Responses are influeced by number, type and cellular location of the system. Has a variation in magnitude and duration of cellular response.

2. Receptor, transmittance of ligand binding, intracellular responses (second messengers, kinase systems)

Front 25

1. What is endocrine signaling?

2. What is paracrine signaling?

3. What is autocrine signaling?

Back 25

1. Distant target cells.

2. Adjacent target cells.

3. Target sites on the same cell.

Front 26

What are cell-surface receptors as compared to intracellular receptors?

Back 26

Ligand binds to the surface, whereas small hydrophobic signal molecule passes through membrane and binds in the nucleus.

Front 27

1. What is the binding equation for ligands?

2. What do the symbols in the equation stand for?

Back 27

1. theta (% bound) = 1 / (1 + Kd/[L]) = [LR] / [Rt]

2. [LR] = bound receptors, [Rt] = number of total receptors, [L] = concentration of ligand

Front 28

1. Do you expect the binding % to be linear with [L] closer at small concentrations or large concentrations? Why?

2. With fewer receptors do you need more or less [L] to get a response?

Back 28

1. At small, to stay with the binding curve of ligand binding. Eventually, at higher concentrations, levels out (reaches saturation).

2. Much more.