Lecture 15

Question 1

How does cholesterol affect fluidity?

Answer 1

• it acts as a bidirectional regulator
• it alters flexibility and packing of lipids
• cholesterol added to liquid crystal DECREASES fluidity
• cholesterol added to crystalline gel INCREASES fluidity

Question 2

Phospholipid Strucutre

Answer 2

Left side: schematic drawing
Right side: space-filling model
Middle: formular

Question 3

Biological Membrane Structure

Answer 3

• flexible
• stable
• self assembly

Question 4

How do lipids affect membrane fluidity?

Answer 4

• Unsaturated lipids INCREASE fluidity

- Saturated lipids DECREASE fluidity

Question 5

PM Dynamics

Answer 5

• Lipids move easily, laterally w/in leaflet
• movement to other leaflet is difficult and slow
• MEMBRANE PROTEINS DIFFUSE W/IN BILAYER
  - protein movement= restricted
  - rapid movement= spatially limited
  - long range diffusion= slow

Question 6

Do diff membranes contain diff lipids and proteins to have diff functions?

Answer 6

yes

Question 7

Biological Membrane Fluid Mosaic

Answer 7

Describes membrane properties.
Fluid: individual lipid molecules move
Mosaic: diverse “particles” allow to penetrate lipid layer (proteins, etc.)

Question 8

Are Biological membranes symmetrical or asymmetrical?

Answer 8

asymmetrical: 2 leaflets w/ distinct lipid composition in plasma membranes where outer leaflet have glycolipids and glycoproteins

Question 9

3 Membrane Protein Classes

Answer 9

Integral-membrane proteins span the lipid bilayer
Peripheral- membrane proteins associated w/ surface of the lipid bilayer
Lipid- anchored- proteins attach to lipid in bilayer

Question 10

Phospholipid Synthesis

Answer 10

• Synthesis occurs at the interface of cytosol and outer ER since they have all molecular machinery (enzymes) for synthesis and distribution
• multistep process, needs many effectors to help
• eventually, vesicle falls off ER w/ phospholipids meant for ectoplasmic cellular membrane on inner leaflet

Question 11

PM & Phospholipids

Answer 11

• lipid molecules like phospholipids, spontaneously aggregate to bury their hydrophobic tail to expose their hydrophilic heads to water
• molecule is ALWAYS at its most stable conformation

Question 12

Integral Protein Functions

Answer 12

• Diff integral proteins have diff functions: nutrient transportation, cell to cell communication, atachemment

Question 13

Plasma Membrane

Answer 13

• most studied cell membrane
• PM= plasma membrane
• SR= sarcoplasmic reticulum
• red blood cells help learn about it since they don’t have nuclei or internal membranes

Question 14

What type of molecules are phospholipids?

Answer 14

Amphipathic molecules: hydrophobic and hydrophilic regions

Question 15

How does temperature affect the fluidity of biological membranes?

Answer 15

• Warming INCREASES fluidity: liquid crystal

- Cooling DECREASES fluidity: crystalline gel

Question 16

Hydrophobic VS. Hydrophilic

Answer 16

Hydrophobic: repelled by water, not attracted to H2O
Hydrophilic: attracted to H2O, dissolved by water

Question 17

What is there to balance ordered and disordered structures?

Answer 17

• mechanical support and flexibility
• membrane assembly and modification
• dynamic interactions between membrane components

Question 18

How can lipid composition change?

Answer 18

1) destruction of lipids (fatty acids)

2) exchange if lipid chains (fatty acids)

Question 19

What is a Trilaminar structure?

Answer 19

a phospholipid bilayer- 6 nm thick