Lecture 1: The Lipid Bilayer

Question 1

What are three main functions of a membrane?

Answer 1

1. separate the inside/outside. (but have a permeability barrier)
2. allow shape change to accommodate growth and movement (fluidity)
3. permit molecule exchange with the environment (selectively permeability)

Question 2

What form the bilayers of membranes?

Answer 2

Lipids

Question 3

These are the active components of signal transduction and transport:

Answer 3

proteins

Question 4

Name 1 similarity of lipids

Answer 4

Amphiphatic character

More specifically, hydrophilic and hydrophobic heads

Question 5

Lipids differ in five main categories. What are these differences?

Answer 5

1. Head Group
2. The number of unsaturated bonds
3. Length of the hydrophobic tail
4. Backbone
5. Shape

Question 6

When in an aquesous environment, lipids will arrange in a way so that their hydrophobic tails are away from water, and their hydrophilic heads face towards water. Why is this?

Answer 6

This arrangement leads to the most energetically favorable state.

Question 7

What is the thickness of the hydrophobic core of a lipid bilayer?

Answer 7

3nm

nanometers

Question 8

Why will the lipid bilayers will seal spontaneously?

Answer 8

This is the most energetically favorable. When planar, the edges are exposed to water. When rounded, there is no exposure.

Question 9

What three things of lipids occur spontaneously and may be measured?

Answer 9

1. Lateral Diffusion
2. Flexion
3. Rotation

Question 10

The switch from one leaflet to the opposite does not occur spontaneously as this is energetically unfavorable. This process is specifically known as what? Additionally, what would it require?

Answer 10

1. Lipid flip-flop

2. Requires “flippase”

Question 11

What is a critical membrane component?

Answer 11

Cholesterol

Question 12

T/F: Cholesterol is found in prokaryotes

Answer 12

False, it is not found in proks

Question 13

Cholesterol is what kind of steroid? Related steroids are found in fungi

Answer 13

Amphiphatic steroid

Question 14

Describe the mechanism of cholesterol with respect to the membrane. (general)

Answer 14

It will insert into the outer part of the outer membrane leaflet. Lipids in the cholesterol stiffened region will become partly immobilized.

Question 15

T/F: The lipid composition of a membrane will determine its properties

Answer 15

True

Question 16

Name the three properties determined by lipid composition.

Answer 16

1. Thickness
2. Membrane Curvature
3. Fluidity

Question 17

Define Fluidity

Answer 17

Ability of a membrane to adopt different shapes without becoming leaky (aka permeable)

Question 18

Cholesterol will regulate membrane _____

Answer 18

fluidity. Specifically the ability of fatty acid tails to interact with each other will determine this

Question 19

T/F: Cholesterol maintains bad fluidity at different temperatures

Answer 19

False, it maintains good fluidity.

Question 20

At a hot temperature, Chol will prevent lipids from ____.

Answer 20

It will prevent them from moving too much, therefore the membrane does not become too fluid (leaky)

Question 21

At a cold temp, Chol will prevent lipids from ____.

Answer 21

being packed too tightly, the membrane remains fluid and does not freeze

Question 22

If a cell does not produce cholesterol (proks), how else can it prevent its membrane from becoming too fluid (leaky) or too stiff (breaks)?

Question 23

In the treatment of athletes foot (tinea pedis), Ketoconazole will interfere with the synthesis of ergosterol (cholesterol-like molecule in fungi). Why does Ketoconazole work as an anti-fungal?

Question 24

How are lipids arranged in the membrane, and why is that important? (with respect to symmetry)

Answer 24

Lipids are arranged asymmetrically. The bilayer asymmetry is important for cell function

Question 25

Lipid bilayers contain a ________ core (about 3nm thick), which are fluid and impermeable to ___ molecules

Answer 25

1. hydrophobic | 2. charged

Question 26

Which factors are likely to lead to a decrease in membrane fluidity? A: An increase in the number of unsaturated bonds in the hydrophobic tail of phospholipids B: An increase in the activity of a lipid flippase C: A change in the molar ratio of PC to PE D: An increase in the number of phospholipids with long hydrophobic tails

Question 27

``` Which of the following organisms is most likely to have the highest percentage of unsaturated fatty acid chains in their membranes? A: Antarctic bacterium B: Desert iguana C: Human being D: Polar bear E: Thermophilic bacterium ```

Question 28

Review - Draw a eukaryotic cell with all its membranes. Which leaflet of a membrane faces a.) the inside of a vesicle b.) the inside of an organelle. Such as the ER? Note: highlighting cytoplasmic leaflets vs exoplasmic leaflets may help!!!

Question 29

Which of the following provides the BEST explanation for why Ketoconazole is a successful anti-fungal drug? PM = Plasma membrane A: It kills by reducing the thickness of the fungal PM B: It kills by decreasing the fluidity of the fungal PM C: It kills by preventing ergosterol incorporation into the fungal PM. D: It kills by increasing the fluidity of the fungal PM E: It kills by inducing vesicle budding from the fungal PM

Question 30

Tthe thickness of the lipid bilayer is influenced by the presence of cholesterol. What will happen when cholesterol is present? If sphingolipids and cholesterol are present?

Answer 30

Cholesterol will straighten it to make it taller. If sphingolipids plus chol are present, no change will occur.