Cell Membranes and Polarity

Question 1

Describe lipid bilayer

Answer 1

Hydrophilic cytoplasmic side, hydrophobic interior, hydrophillic ECM side

Question 2

Lipid-protein interactions are:

Answer 2

Noncovalent. Allows for fluidity amongst them

Question 3

Miscelle is made when….What is its double FA counterpart called?

Answer 3

1. Put strands of SINGLE FA chains in polar environment

2. Liposome. Becomes a sphere. Hydrophillic exterior, hydrophobic interior.

Question 4

What’s a phosphoglyceride?

Answer 4

Glycerol backbone, 2 FA’s attached (one is not saturated, so it’s kinked to increase fluidity), and phosphate group (- charge) = polar head.

Question 5

Phosphatidyl serine:

Answer 5

Has net (-). Kind of phosphoglyceride.

Question 6

Phosphatidyl-ethanolamine and Phosphatidyl Choline

Answer 6

phosphoglycerides, both have neutral charge

Question 7

Sphingomyelin:

Answer 7

derived from sphingosine, has 2FA’s and AMINE group

Question 8

Cholesterol = ?

Answer 8

Sterol, POLAR because it HAS an OH. Located at membrane surface. Rigid ring structure stiffens some parts of membrane, but aliphatic components keep the FA’s apart.

Question 9

Glycolipids = ?

Answer 9

has 2FA’s and sugar (charged or uncharged) intsead of phosphate (looks like sphingosine)

Question 10

Give description of composition of lipid membrane:

Answer 10

Cholesterol + sphingomylin = less internal part of plasma membrane
Phosphatidyl ethanolamine + phosphatidyl choline = internal part of membrane
Glycolipid: not much lie in internal membrane
Protein distribution = asymmetric between the two sides of the layer.

Question 11

Bacteria have cholesterol (T/F)

Answer 11

F: Bacteria (and plants) have a cell wall, which has no cholesterol.

Question 12

How often does the membrane move?

Answer 12

Lateral diffusion (left and right movement) as well as rotations = quite common. However, very little flipping

Question 13

Describe relative locations of different proteins in the layer.

Answer 13

Phosphotidyl serine: alwasy internal in order to participate in kinase receptor mech
Phosphatidyl choline, sphingolipids, and glycolipids = ECM side.
Cholesterol = both sides

Question 14

What is a lipid raft?

Answer 14

NON-random lipid distribution in inner or outer membrane. Cholesterol + sphingomyelin. Thicker FA chain consistency.

Question 15

What can be used for signaling purposes?

Answer 15

phosphatidylinositol (PiP2 cleaved to iP3)

Question 16

What is an integral membrane protein?

Answer 16

Permanent in membrane. Stretch of hydrophobic AA. In case of alpha helix, 100% internal. In case of barrel beta sheet, hydrophobic exterior with hydrophobic interior.

Question 17

Peripheral membrane proteins = ?

Answer 17

Proteins attached covalently but can be removed. Can also be used for signaling.

Question 18

Name some protein membrane attachments

Answer 18

Amide linkages and thioester linkages with cystein. Both are reversible.

Question 19

So, what crosses the membrane?

Answer 19

Hydrophobic molecules (O2, CO2, N2, steroids). All else, small or large will not pass.

Question 20

Describe a channel transporter

Answer 20

Transports ions, not very specific, flow = down concentration gradient. no energy needed. FAST transfer.
Tetrotodoxin = Na+ channel blocker.
Lidocaine = anesthetic, treats tachy heart
K+ blockers: treats arrhythmias.
Nicotinic acetylcholine receptor: Na+/K+ channel at neuromuscular jxn.
Curere: antagonist for Ach.

Question 21

Describe a carrier

Answer 21

Binds molecule on one side, switch conformation (physical change, not chemical), release solute on other side. No energy needed. Medium speed.
Uniport: 1 molecule transport. Ex: Glut1 (glucose transporter)
Synport: transports 2 molecules at once, one of which is going against its concentration gradient. FASTER than DIFFUSION. Ex: Na+-Glucose, where glucose is going against. Overcome Na+ cell saturation by using Na/K pumps to pump out excess Na+ from the cell.

Question 22

Describe a pump transporter

Answer 22

Transfer AGAINST gradient. Need ATP, Slowest.
P-Type: cleaves ATP to phosphorylate itself and change conformation. Pumps ions.
Ex: Pushes Ca2+ into SER for muscle contraction.
EX: Na+/K+ pump, which shoves both molecules against concentration gradient (Na_ exits the cell, K+ enters)
ABC: ATP Binding Cassette: uses 2 atpases, transports small molecules. Both binding sites need atp. Sends molecules outside cell.
Ex: ABC transporters (MOLECULES, not IONS, except in case of CFTR) helps with tumor’s drug resistance. once it multiplies, no drug can help.

Question 23

What determines rate of carrier transport?

Answer 23

Km, and flip rate (Vmax)