1 - Membrane Structure and Proteins

Question 1

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

Answer 1

Sugar residues are exposed to 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

• Cell metabolism
• formation of myelin sheaths
• membrane turnover

Question 6

What are the two major classes of membrane proteins?

Answer 6

• Peripheral
• 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 membrane by weight)

Question 10

Carbohydrates on membrane proteins are always exposed to _________ surface

Answer 10

Carbohydrates on membrane proteins are always exposed to 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

• Small polar uncharged molecules (eg CO2, urea, glycerol)
• Hydrophobic molecules (O2, N2)

Question 13

What are the two forms of transport through carrier proteins?

Answer 13

• Facilitated diffusion
• Active transport

Question 14

What is the difference between facilitated diffusion and active transport?

Answer 14

Associated with carrier proteins

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

Question 15

What are three methods of gating ion channels?

Answer 15

• voltage operated
• ligand operated
• 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

• scaffolding protein
• 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