Lecture 23 Flashcards
What happens when you put amphiphilic molecules in a non polar environment?
They tend to arrange themselves so that the nonpolar portions of their structure are away from interactions from aqueous solvents
What do Glycerophospholipids do when you place them in aqueous environments?
They tend to form bilayer structures like liposomes
What is a Liposome?
A small spherical structure that contains a bilayer of membrane lipids
What kind of environments do Liposomes create?
Distinct environments that are separate from each other. An interior and exterior environment. Inner leaflets and outer leaflets
Why is it important to form the distinction between inner leaflets and outer leaflets in liposomes?
Because in more complex structures it makes a difference weather it is in a cytoplasmic environment or exterior environment
How can liposomes be used for various different purposes?
Water soluble drugs can be placed in the center. Lipid soluble drugs can be placed in the bilayer portion
Why are Glycerophospholipids able to form phospholipids and triacylglycerols are not?
- 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
What causes Bilayers to vary?
- Acyl chain
* Polar head group
What kind of associations are formed between one lipid molecule in a bilayer and another?
Non-covalent associations
What does the non-covalent interactions between the lipids in a bilayer allow for?
It allows for stability but fluidity of the membrane
What are the characteristics of a bilayer with short acyl chains?
The bilayer will be thinner
What do the OH groups of cholesterol associate with in the bilayer?
The polar headgroups
What happens to a bilayer below the transition temperature?
- Acyl chains pack together in van der waals contact
* Bilayer is in a gel-like solid state
What happens to a bilayer above the transition temperature?
Lipid molecules and their acyl chains move freely and rapidly
What is the melting temperature (transition temperature) of a lipid bilayer?
The temperature of its transition from an ordered crystalline to a more fluid state, and depends on acyl-chain unsaturation and length
What does the transition temperature of a bilayer depend on?
The acyl-chain unsaturation and length
What type of membranes have a sharp transition temperature?
Artificial membranes that have one type of lipid
What is the transition temperature for biological membranes usually like?
It is not typically sharp
Why is the transition state for not usually sharp?
•Because it is a mixture of different compounds (different lipids/proteins)
How can a membrane maintain a fluid state at different temperatures?
- Introduce double bonds
* Changing the length of fatty acids
What changes will be seen in the bilayer with decreasing temperature and why?
- More unsaturated fatty acids
- Shorter fatty acids
- To lower the melting point
What changes will be seen in the bilayer with increasing temperature and why?
- More saturated fatty acids
- Longer fatty acids
- To increase melting point
What does Cholesterol do to membranes in mammals?
It increases membrane rigidity and fluidity
How does Cholesterol limit the acyl cells?
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
