Chapter 6: 6.2 Membranes

Question 1

Different membranes have different —– ——–

Answer 1

Lipid profiles

Question 2

What are membranes made up of?

Answer 2

A variety of lipids and proteins

Question 3

What do the membrane compositions represent?

Answer 3

Represents a fluid mosaic model

Question 4

What diffuses rapidly throughout the plane of the membrane?

Answer 4

Lipids

Question 5

True or False:

In membranes, protein composition is always the same

Answer 5

False, protein composition is random

Question 6

Protein are able to travel ——— throughout the membrane

Answer 6

Laterally

Question 7

What forces are involved in membrane lipid assembly?

Answer 7

1. Hydrophobic effect
2. Van der Waals forces

Question 8

Different lipids yield different membranes, what lipid shapes are there?

Answer 8

1. Cone
2. Cylinder

Question 9

Why do polar lipids aggregate?

Answer 9

To minimize contact between water and their hydrocarbon chains

Question 10

What do cone shaped lipids form?

Answer 10

Micelles

Question 11

What do cylinder shaped lipids form?

Answer 11

Bilayers

Question 12

What does membrane fluidity depend on in the membrane?

Answer 12

Lipids within the membrane

Question 13

List:

Properties of lipids that affect membrane fluidity

Answer 13

1. Saturation
2. Hydrocarbon length
3. Cholesterol
4. Headgroup

Question 14

Define:

Tm

Answer 14

Phase Transition Temperature
* Midway point between gel-like and fluid membranes

Question 15

Describe:

Structure of membrane hydrocarbons as it moves from solid to fluid

Answer 15

Hydrocarbons chang from anti-conformation to gauche conformation resulting in more “kinks”

Question 16

What R Groups affect Tm?

Answer 16

• Choline
• Ethanolamine
• Glycerol

Question 17

True or False:

The longer the chain length, the higher the Tm

Answer 17

True

Question 18

The tighter the packing of the kipids…

Answer 18

The more solid the membrane

Question 19

At lower temperatures, membranes have more…

Answer 19

Unsaturated hydrocarbon chains

Question 20

At higher temperatures, membranes have more…

Answer 20

Saturated hydrocarbon chains

Question 21

What does cholesterol act as in membrane fluidity?

Answer 21

Cholesterol acts as a “buffer”

Question 22

What does it mean that cholesterol acts as a “buffer”?

Answer 22

It disrupts lipid packing as well as provides rigidity

Question 23

Describe:

High Temperature Adaptations of Hypothermophilic Archaea

Answer 23

Have a lipid called caldarchaeol
* Stabilizes the membrane even more at high temperatures

Question 24

What high temperature adaptations are present on hydrocarbons chains?

Answer 24

Hydrocarbon chains are linked with glycerol at both ends

Question 25

# Describe: Membrane Lipid Dynamics

Answer 25

Lipids move laterally in the membrane very rapidly (1 μm/s) * Transverse diffusion is much slower

Question 26

Why is transverse diffusion so much slower?

Answer 26

The polar head group does not easily pass through the hydrophobic interior

Question 27

# In transverse diffusion: What move lipids from the outer membrane to the inner membrane?

Answer 27

Flippases

Question 28

# In transverse diffusion: What moves lipids from the inner membrane to outer membrane?

Answer 28

Floppases

Question 29

# In transverse diffusion: What transports lipids from either side of the membrane to the other?

Answer 29

Scramblases

Question 30

# Define: FRAP

Answer 30

Fluorescence Recovery After Photobleaching

Question 31

# State: Steps of FRAP

Answer 31

1. Fluorescently label lipids 2. Bleach membrane 3. Monitor how quickly fluorescence returns

Question 32

What does FRAP show?

Answer 32

Show that lipids rapidly diffuse laterally

Question 33

# Describe the process of: Freeze Fracture EM of the Membrane

Answer 33

1. Freeze cells to -196°C in liquid nitrogen 2. Fracture membrane )opens along interface of lipids) 3. Separate the two halves 4. Make a carbon-metal replica of each half 5. Observe via electron microscopy (EM)

Question 34

What can freeze fracture EM of the membrane show?

Answer 34

Shows that membrane protein distribution is random

Question 35

# Describe the process of: Single Molecule tracking of Phospholipids/proteins

Answer 35

1. Label phospholipid/protein 2. Place in a live kidney (contains compartments) 3. Track with microscope

Question 36

What can single molecule tracking of phospholipids/proteins?

Answer 36

Shows that lipids diffuse quickly and freely between compartments, but protein remained contained within compartments longer

Question 37

What can diffusion be impeded by? (4)

Answer 37

1. Actin cytoskeleton barriers on the underside of membrane 2. Organelle membranes contacting the plasma membrane 3. Extracellular matrix linked to the membrane proteins 4. Immobile membrane protein and lipid clusters