Term
| What structures can lipids spontaneously form in aqueous solutions? |
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Definition
| Micelles, bilayers, liposomes |
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Term
| Why do lipids form micelles? |
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Definition
| To increase entropy (because fewer H20 molecules are ordered) and to increase stability |
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Term
| What determines whether a lipid will form a micelle or if it will form a bilayer? |
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Definition
If one hydrophobic tail- micelle,
if two tails- bilayer |
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Term
| What molecular interactions does formation of lipid bilayers promote? |
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Definition
-Increased entropy (from release of water from tails)
-Van der Walls interactions between hydrocarbon chains
-Electrostatic and H-bonding between polar head groups and water |
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Term
| What molecules are most likely to be able to get through a lipid membrane |
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Definition
| Small, nonpolar, uncharged molecules |
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Term
| List two uncatalyzed movements in a bilayer membrane |
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Definition
Flip-flop (very slow)
Lateral diffusion (very fast) |
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Term
| List three catalyzed movements in a bilayer membrane and the enzymes |
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Definition
-Flippase (flip from outer to inner leaf)
-Floppase (flip from inner to outer leaf)
-Scramblase (moves either direction towards equilibrium) |
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Term
| Describe lipid phase transition |
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Definition
| In a higher temperature, the paracrystalline state (gel-like) changes to a fast-moving fluid state |
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Term
| What does lipid phase transition depend on? |
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Definition
Chain length (shorter= more fluid)
Amount of unsaturated tails (more=more fluid) |
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Term
| What is the role of cholesterol in a bilayer? |
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Definition
Decrease the packing between the tails, lowering the transition temperature
Also, conversely, increases viscosity by limiting movement
Overall, makes transition a more gradual process (unlike in cholesterol-free bacteria) |
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Term
| Is lipid composition the same in all membranes all over the body? |
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Definition
Generally similar, but not the same
For example, mitochondria has much higher amounts of cardiolipid
Red blood cells have much more sphingolipids
Neurons have a lot of glycolipids |
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Term
| What is notable about the lipid composition of mitochondria and E. coli membranes? |
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Definition
They both have high cardiolipin, low phosphatidylserine, low cholesterol
Also, they both depend on an outer membrane for protection against phase transition |
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Term
| Are two monolayers in a single cell's membrane similar in composition? |
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Definition
No
The outer membrane has more phosphotidylcholine and sphingomyelin
The inner monolayer has more of all other lipids |
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Term
| Why does the outer monolayer have more sphingolipids? |
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Definition
| Because of their mode of synthesis, carbohydrate or phosphocholine head groups are attached to a ceramide precursor in the lumen of the golgi that is then vesicle transported to the outer membrane |
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Term
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Definition
An ether lipid with a double bond between the C-1 and C-2 of the ether-linked hydrocarbon chain
Important in heart cells |
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Term
| Why are plasmogens important in heart cells? |
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Definition
| Because their alkenyl ether linkage provides protection against radical oxygen species |
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Term
| Define platelet-activating factor |
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Definition
| An ether-lipid important in signaling in platelet aggregation, inflammation, and the allergic response |
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Term
| What are lipids like in plant chloroplast membranes? |
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Definition
| Plants use galactolipids and sulfolipids in the chloroplast (possibly because of lack of phosphate in the soil) |
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Term
| What are lipids like in archaebacteria membranes? |
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Definition
Very complex, with ether-linkages that are resistant to hydrolysis at low pH or high temperature
A long chain between two glycerol span the width of the bilayer, presumably to provide stabilization (since there's no cholesterol) |
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Term
| What do lipids have to do with blood type? |
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Definition
| On red blood cells, there are glycolipids with oligosaccharide moieties that specify ABO blood type |
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Term
| What new research is being done to create more O-type universal donor blood? |
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Definition
| Glycosidase enzymes from bacteria might be able to effectively remove the extra sugar from A or B antigens on ceramides |
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Term
| Describe the structures of the blood type antigens |
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Definition
Glycolipids
Additional N-acetylgalactosamine = A type
Additional galactose = B type |
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Term
| Define lipopolysaccharide (LPS) |
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Definition
A complex glycolipid only found in bacteria, the major component of gram-negative bacteria
An important target for antibodies and implicated in many pathogenic responses
Endotoxins that trigger immune system cascades (sepsis, toxic shock) |
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Term
| What percentage of a membrane is protein? |
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Definition
50% in an average membrane (by weight), about 1 protein per 50 lipids
30% in myelin, 75% in E. coli |
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Term
| What percentage of a membrane are sterols (cholesterol, etc)? |
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Definition
| 20-25% in animals, absent from E. coli, minor in yeast, protist, and plant |
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Term
| What is the difference between integral and peripheral membrane proteins? |
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Definition
Integral proteins are stuck in the membrane (transmembrane or linked to a lipid); can only detach with detergent
Peripheral can associate with the membrane but detach easily (can dissociate with salt, pH, or chelating agent) |
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Term
| Describe Type I and II membrane proteins |
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Definition
Type I: N-terminus outside
Type II: N-terminis inside |
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Term
| Describe Type III and IV membrane proteins |
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Definition
Type III: Several subunit linked by chain
Type IV: individual subunits with individual chain |
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Term
| Describe Type V membrane proteins |
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Definition
| Type V: No anchoring subunit, linked to lipid group |
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Term
| Describe Type VI membrane proteins |
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Definition
| Type VI: A subunit and a chain that links to a GPI lipid anchor |
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Term
| Describe the membrane protein subunit general structure |
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Definition
Hydrophobic, alpha-helical structures
Alpha-helical in order to group polar side chains together for entropy |
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Term
| Describe bacteriorhodopsin |
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Definition
| A 7-pass (hepta-helical) transmembrane structure involved with G-proteins |
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Term
| How many amino acids are required to span the membrane in an alpha-helix? |
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Definition
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Term
| What is a hydropathy plot used for? |
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Definition
To predict the transmembrane alpha-helical domains (based on the knowledge that it takes 20 AA to span the membrane)
The hydropathy plot would have to show that the protein is hydrophobic |
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Term
| Alpha-helixes are the most common membrane protein structure. However, it's not the only kind. What do beta sheets form? |
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Definition
Beta-barrels that line a cylinder
Often found in bacteria and mitochondria
Not predicted by hydropathy plots (individual chains are too short) |
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