Lecture 6 - Membranes

Question 1

What do membranes do?

Answer 1

define boundaries and serve as permeability barriers
- membranes are needed to separate functions (i.e., proteins are not made in the nucleus)

Question 2

Fluid mosaic models

Answer 2

membrane = a fluid bilayer of lipids
proteins (and other molecules) = mosaic

Question 3

Different types of lipids in membranes

Answer 3

• phospholipids
• glycolipids
• sterols

Question 4

What does it mean that the membrane is asymmetric?

Answer 4

phospholipids diffuse

Question 5

What are translocates?

Answer 5

proteins that move phospholipids between layers and maintain the lipid symmetry
- prevent lipids from being homogenous

Question 6

What are the 3 types of translocases?

Answer 6

1. Flippase: moves lipids inside
2. Floppase: moves lipids outside
3. Scramblase: moves lipids in and out

Question 7

What is FRAP?

Answer 7

Fluorescence Recovery After Photobleaching
- a method to study the mobility of molecules in living cells
- cell surface molecules (i.e., phospholipids) are labeled w/ fluorescent dye
- laser beam bleaches an area of cell surface => fluorescent molecules stop working but does not destroy membrane
- fluorescent-labeled molecules diffuse into bleached area
- bleached area disappears as lipids move laterally

Question 8

Proteins at membrane must have what?

Answer 8

hydrophobic amino acids

Question 9

What kind of proteins do membranes contain?

Answer 9

• integral: have a hydrophobic region
• peripheral: associate through another membrane protein
• lipid-anchored: bind fatty acids which gets inserted into the membrane

Question 10

Types of integral membrane proteins

Answer 10

• integral monotropic protein
• singlepass protein
• multipass protein
• multi-subunit protein

Question 11

Types of lipid-anchored membrane proteins

Answer 11

• fatty acid or isoprenyl anchor
• GPI anchor

Question 12

Membrane proteins _______ and ________ electrical and chemical signals

Answer 12

detect; transmit

Question 13

What can membrane proteins mediate?

Answer 13

cell adhesion and cell-cell communication
- cadherin to cadherin binding keep cells together

Question 14

What are most integral proteins? What can they do?

Answer 14

transmembrane proteins => can move ions across cell membranes

Question 15

Integral monotropic proteins

Answer 15

• only on one side of the membrane
• very rare

Question 16

Peripheral membrane proteins

Answer 16

form weak and reversible associations to the membrane, typically through binding to integral membrane proteins

• do not have hydrophobic parts => cannot be in membrane

Question 17

Lipid-anchored membrane proteins

Answer 17

covalently bound to fatty acids or isoprenyl groups

Question 18

What is an example of a lipid-anchored membrane protein

Answer 18

trehalase - an enzyme that cuts trehalose into 2 glucose molecules
its bound to glycosylphosphatidylinositol

Question 19

Proteins and lipids in the ________ of the membrane are ________

Answer 19

outside; glycosylated

Question 20

What is glycosylation?

Answer 20

the process by which a carbohydrate is covalently attached to a target macromolecule
- N-linked gylcosylation of asparagine
- O-linked glycosylation of serine or threonine