Lecture 7 - Membrane Structure Flashcards Preview

Unit 1 - Molecular and Cellular Principles of Medicine > Lecture 7 - Membrane Structure > Flashcards

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What are the functions of biological membranes?

1. Selective permeability barrier

2. Comparmentalization of functions.

3. Identification

4. Signalling

5. Energy storage


What are common features of biological membranes? 

1. Sheetlike structures that can form closed boundaries in aqueous solution

2. Composed of lipid, protein, and carbohydrate

3. Lipid bilayer is relatively impermable to polar molecules

4. Membrane proteins carry out most specific fxns

5. Membranes are held together by non-covalent interactions

6. Biological membranes are asymmetric

7. Membranes are fluid under physiological conditions


Membrane lipids are .....

AMPHIPATHIC! - both hydrophobic (hydrocarbon tails) and hydrophilic (polar head groups)


Describe the structure of a phospholipid


Describe the effect of saturation and length of fatty acids chains

Increased saturation and increased length leads to decreased fluidity


What confirmation are naturally occuring unsaturated fatty acid chains in?



Describe the general structure of phospholipid backbone and give examples.

Glycerol or sphingosine (in sphingomyelin) - attach to fatty acids and phosphate via hydroxl groups


Glyercol attaches to 2 fatty chains, sphingosine carries on hydrocarbon of its own


What composes a phospholipid headgroups and give some examples

Phosphate + alcohol, ex. serine, choline, inositol, ethanolamine, etc.


What are other components of the membrane?

Glycolipids - sphingosine backbone w/ sugar attached

Cholesterol - makes membrane less flexible


Memorize the amphipathic properties of membrane lipids...


What are the forces at play in the spontaneous formation of lipid bilayers?

Hydrophobic effect, van der Waals, electrostatic and H bonding


What is the difference between transverse and lateral diffusion of membrane lipids

Transverse (flip flop) - very slow, protein mediated

Lateral - all the fucking time, gives fluidity


What are factors affecting fluidity?

1. Temp - needs to be above "melting temperature" to be fluid and free flowing

2. Length and degree of unsaturation of fatty acid chain - shorter, unsaturated = ^^ fluidity

3. Cholesterol content - decreases fluidity (lipid rafts)


What factors make a substance imperable to a lipid bilayer?

1. Polarity - ^ polarity means it won't get through

2. Size - the larger the molecule, the more difficult it will be to get through


How do drugs get into cells?

1. Passive diffusion

2. Hijacked transporters

3. Liposome delivery

4. Protein transduction


What is the relative ratio of lipid to proteins in the membrane?

Differs but around 1:1, there's more protein than people think


Types of membrane proteins...

Integral membrane proteins - transmembrane, monolayer associated, lipid linked - amphipathic to be inserted into membrane

Peripheral membrane proteins - protein attached


Fluid mosaic model

1. Lipid bilayer acts as solvent for membrane proteins

2. Membrane proteins are free to diffuse laterally, but cannot flip-flop


How can lateral diffusion of membrane proteins be constrained?

1. Anchoring protein to intracellular structure

2. Anchoring protein to extracellular structure

3. Protein/protein interactions b/n cells

4. Barriers by junction proteins


Describe lipid rafts

Regions of membrane that are more rigid and resistant to solubilization

Specific proteins are recruited for...

1. Signal transduction

2. Protein sorting

3. Recognition

4. Viral entry/exit


Describe some special properties of lipids in a membrane

Abnormal lipid distribution signal cells are dying