Lecture 23

Question 1

What happens when you put amphiphilic molecules in a non polar environment?

Answer 1

They tend to arrange themselves so that the nonpolar portions of their structure are away from interactions from aqueous solvents

Question 2

What do Glycerophospholipids do when you place them in aqueous environments?

Answer 2

They tend to form bilayer structures like liposomes

Question 3

What is a Liposome?

Answer 3

A small spherical structure that contains a bilayer of membrane lipids

Question 4

What kind of environments do Liposomes create?

Answer 4

Distinct environments that are separate from each other. An interior and exterior environment. Inner leaflets and outer leaflets

Question 5

Why is it important to form the distinction between inner leaflets and outer leaflets in liposomes?

Answer 5

Because in more complex structures it makes a difference weather it is in a cytoplasmic environment or exterior environment

Question 6

How can liposomes be used for various different purposes?

Answer 6

Water soluble drugs can be placed in the center. Lipid soluble drugs can be placed in the bilayer portion

Question 7

Why are Glycerophospholipids able to form phospholipids and triacylglycerols are not?

Answer 7

• Glycerophospholipids are amphipathic and aggregate into bilayers that can interact with water on both sides
• They also have to acyl chains that align easily to form the side by side to form a bilayer
• Triacylglycerols are not amphipathic

Question 8

What causes Bilayers to vary?

Answer 8

• Acyl chain

* Polar head group

Question 9

What kind of associations are formed between one lipid molecule in a bilayer and another?

Answer 9

Non-covalent associations

Question 10

What does the non-covalent interactions between the lipids in a bilayer allow for?

Answer 10

It allows for stability but fluidity of the membrane

Question 11

What are the characteristics of a bilayer with short acyl chains?

Answer 11

The bilayer will be thinner

Question 12

What do the OH groups of cholesterol associate with in the bilayer?

Answer 12

The polar headgroups

Question 13

What happens to a bilayer below the transition temperature?

Answer 13

• Acyl chains pack together in van der waals contact

* Bilayer is in a gel-like solid state

Question 14

What happens to a bilayer above the transition temperature?

Answer 14

Lipid molecules and their acyl chains move freely and rapidly

Question 15

What is the melting temperature (transition temperature) of a lipid bilayer?

Answer 15

The temperature of its transition from an ordered crystalline to a more fluid state, and depends on acyl-chain unsaturation and length

Question 16

What does the transition temperature of a bilayer depend on?

Answer 16

The acyl-chain unsaturation and length

Question 17

What type of membranes have a sharp transition temperature?

Answer 17

Artificial membranes that have one type of lipid

Question 18

What is the transition temperature for biological membranes usually like?

Answer 18

It is not typically sharp

Question 19

Why is the transition state for not usually sharp?

Answer 19

•Because it is a mixture of different compounds (different lipids/proteins)

Question 20

How can a membrane maintain a fluid state at different temperatures?

Answer 20

• Introduce double bonds

* Changing the length of fatty acids

Question 21

What changes will be seen in the bilayer with decreasing temperature and why?

Answer 21

• More unsaturated fatty acids
• Shorter fatty acids
• To lower the melting point

Question 22

What changes will be seen in the bilayer with increasing temperature and why?

Answer 22

• More saturated fatty acids
• Longer fatty acids
• To increase melting point

Question 23

What does Cholesterol do to membranes in mammals?

Answer 23

It increases membrane rigidity and fluidity

Question 24

How does Cholesterol limit the acyl cells?

Answer 24

Because it is rigid and planar it can sit between the two acyl tails and increase van der Waals interactions causing them to be rigid

Question 25

What does Cholesterol do at low and high temperatures?

Answer 25

• Low temps: Prevents close packing between acyl chains

* High temps: Decreases motion/disorder of acyl chains, increases rigidity

Question 26

In which direction can lipids move freely in the bilayer?

Answer 26

Laterally

Question 27

Why can’t lipids move from one leaflet to another rapidly (transverse)?

Answer 27

Because it is energetically unfavorable

Question 28

What do Flipases do?

Answer 28

Increase the rate of transverse diffusion

Question 29

In what organisms is E.coli present?

Answer 29

It is present in mammals only

Question 30

What are the three types of membrane proteins?

Answer 30

• Integral membrane proteins
• Peripheral membrane protein
• Lipid-linked protein

Question 31

Through what interactions do integral binding proteins associate with lipids?

Answer 31

Through hydrophobic interactions

Question 32

What is the phobicity of the portion of the integral membrane protein surface that interacts with the acyls?

Answer 32

It is hydrophobic

Question 33

How do peripheral membrane proteins interact with the lipid bilayer?

Answer 33

Through electrostatic interactions. Charge charge and H-bond

Question 34

What are Lipid-linked proteins?

Answer 34

Proteins that contain a lipid prosthetic group

Question 35

How do Lipid-linked proteins associate with the membrane?

Answer 35

The anchor is covalently attached to the polypeptides