1 - Membrane Structure and Proteins

Question 1

Proteins and lipids may be glycosylated, which side of the membrane are these sugar residues exposed to?

Answer 1

Sugar residues are exposed to the extracellular milieu only

Question 2

What are the three primary components of the lipid bilayer?

Answer 2

Phospholipids, cholesterol, and glycolipids

Question 3

_________ fatty acids cause a kink in the acyl chain which reduces interactions between lipids of the bilayer to promote lateral diffusion (makes membrane more fluid)

Answer 3

Unsaturated fatty acids cause a kink in the acyl chain which reduces interactions between lipids of the bilayer to promote lateral diffusion (makes membrane more fluid)

Question 4

What effect does cholesterol have on the lipid bilayer?

Answer 4

Bidirectional regulation

• At high temperatures cholesterol stabilizes the membrane and raises its melting point = decrease fluidity
• At low temperatures cholesterol intercalates between phospholipids and prevent them from clustering together and stiffening = increases fluidity

Question 5

What are 3 roles of glycolipids in the lipid bilayer?

Answer 5

1. Cell metabolism
2. Formation of myelin sheaths
3. Membrane turnover

Question 6

What are the two major classes of membrane proteins?

Answer 6

1. Peripheral
2. Integral

Question 7

How are peripheral membrane proteins removed from the membrane?

Answer 7

High extracellular salt concentrations

Question 8

How are integral membrane proteins removed from the membrane?

Answer 8

Require disruption by a detergent to remove

Question 9

Most plasma membrane proteins are _________ (accounts for 2-10% of membrane by weight)

Answer 9

Most plasma membrane proteins are glycosylated (accounts for 2-10% of the membrane by weight)

Question 10

Carbohydrates on membrane proteins are always exposed to _________ surface

Answer 10

Carbohydrates on membrane proteins are always exposed to the extracellular surface

Question 11

What are membrane carbohydrates important for?

Answer 11

cell-cell interactions, cell recognition

Question 12

Which molecules can pass through the plasma membrane?

Answer 12

1. Small polar uncharged molecules (eg CO2, urea, glycerol)
2. Hydrophobic molecules (O2, N2)

Question 13

What are the two forms of transport through carrier proteins?

Answer 13

1. Facilitated diffusion
2. Active transport

Question 14

What is the difference between facilitated diffusion and active transport?

Answer 14

Associated with carrier proteins

1.Facilitated diffusion:
* Passive
* Requires concentration gradient
* Carrier molecule facilitates the diffusion past the membrane
2. Active transport
* Requires energy
* Can concentrate substances against their gradient

Question 15

What are three methods of gating ion channels?

Answer 15

1. voltage operated
2. ligand operated
3. mechanically operated (stretch or compression)

Question 16

What is N-CAM?

Answer 16

Neural cell adhesion molecule

an immunoglobulin-like neuronal surface glycoprotein which binds to a variety of other cell adhesion proteins to mediate adhesion, guidance, and differentiation during neuronal growth

Question 17

What is a gap junction?

Answer 17

Hemichannel formed by aggregates of connexins

interacts with hemichannels from other cell to form gap junction

• conduct ionic current

Question 18

What are three cytoplasmic proteins?

Answer 18

-Actin
-Ankyrin
-Spectrin

Question 19

Role of actin as a cytoplasmic protein?

Answer 19

Forms nodal points under membrane - maintain cell shape

Question 20

Role of ankyrin as a cytoplasmic protein

Answer 20

1. scaffolding protein
2. link the membrane-bound (intrinsic) proteins to the underlying cytoskeleton.
   -This function of ankyrins contributes to the expression, specific localization, and overall stability of membrane proteins within the plasma membrane.

Question 21

Role of spectrin as a cytoplasmic protein

Answer 21

Spectrin forms the network between the actin nodes to maintain plasma membrane integrity and cytoskeleton structure