Term
| What are the major functions of biological membranes (5)? |
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Definition
1) Retain nutrients
2) Obtain nutrients from environment
3) Chemical charge gradient (inside low Na and high K)
4) Retain synthesized materials
5) Waste exocytosis |
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Term
| What are the 3 primary functions of lipids in cells? |
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Definition
1) long term energy storage
2) building blocks of signaling molecules, steroids
hormones and lipid derived cytokines (arachadonic acid)
3) Structural core of biological membranes (phospholipids, sphingolipids, cholesterol) |
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Term
1) Discuss the primary function and structure of phospholipids.
2) How are they degraded?
3) Why is phosphatidic acid (PA) of particular importance? |
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Definition
1) Membrane structure and fluidity
Amphipathic (polar and nonpolar ends)
Glycerol backbone
2 FA (normally 1 saturated and 1 unsaturated)
Head group (can be +, - or neutral)
Phosphate group
2) Phospholipases A1, A2, C and D hydrolize ester bonds.
3) PA (extra phosphate group) increases membrane curvature and is important for vesicle formation. It also acts as a signaling molecule to recruit cytosolic molecules to vesicle-forming sites. |
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Term
1) Discuss the primary function and structure of sphingolipids
2) What are 4 subdividision of sphingolipids |
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Definition
1) Amphipathic with polar head and two nonpolar tails
Building block is sphingosine
Instead of glycerol, 3C backbone presents -OH, -NH2 (becomes ceramide when FA is attached here) and -OH, respectively.
2) a) Sphingomyelin (myelin sheath around peripheral nerves and in white matter of CNS as well as lipid rafts)
b) Cerebrosides- single sugar linked to ceramide (those with galactose are in neural tissue, those with glucose are in non-neural tissue)
c) Glycolipids- 2-6 sugar molecules linked to ceramide in exoplasmic face of PM important for blood type (type A blood is NAG and type B blood is galactose), tumor antigens, cell surface receptors and embryonic antigens
d) Gangliosides are complex sugars and comprise 6% of grey matter lipid in CNS |
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Term
| A patient is looking for a blood transfusion and they are Type A. What type of terminal sugar would have to be expressed on the glycolipids of cells from the donor? |
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Definition
1) Remember, the terminal sugars of glycoplipids are important for determining blood type, as well as acting as tumor antigens and cell surface recetors
Type A is NAG
Type B is Galactose
Type AB is NAG & Galactose (universal acceptor)
Type O is neither (universal donor) |
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Term
| Cholesterol is a largely hydrophobic (four hydrocarbon rings and a hydrocarbon tail), but is slightly hydrophilic (hydroxyl group that interacts with water). What consequences does this structure have in terms of its ability to interact in membranes? |
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Definition
| Cholesterol is too hydrophobic to form sheets on its own, but it can interact with phospholipids |
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Term
| Which major lipids in mammalian cell membranes have a net negative charge (2)? Which ones are electrically neutral at physiological pH (3)? |
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Definition
(-) Phosphatidylserine and Phosphatidylinositol
(+/-) Phosphatydylcholine, cholesterol and sphingomyelin |
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Term
| Would a membrane composed of short fatty acid chains and unsaturated "cis" fatty acids create a gel phase membrane or a sol phase membrane? |
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Definition
sol (liquid, disorganized).
This question requires a few points of prior knowledge.
First, short FA chains and unsaturated "cis" fatty acids have less surface area of contact within the membrane and are therefore more fluid and random.
"sol" stands for "liquid, disorganized" and "gel" stands for "solid, organized." In this case, the answer is more fluid, so it is "sol." |
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Term
| How does cholesterol stabilize membrane fluidity? |
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Definition
Short answer-By promoting the "liquid, organized state" and preventing the hydrocarbon tails of phospholipids from "gel-ing."
The steroid rings of cholesterol intercalate b/w hydrocarbon tails of phospholipid, expanding the temperature range in which lateral diffusion can take place. At slightly warmer temperatures, cholesterol decreases membrane fluidity, but at cooler temperatures, it maintains fluidity by preventing hydrocarbon chains from "geling." In general, cholesterol promotes the "liquid, organized state." |
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Term
| True:False "Flip-flop" of lipids in membranes is a non-spontaneous process which requires "flip-flop" carrier proteins. |
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Definition
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Term
| How does the gp120 surface protein of HIV contribute to viral fusion with host-cells? |
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Definition
| It binds to sphingomyelin in lipid rafts and induces a conformational change! |
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Term
| How do lipid rafts act in membranes? |
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Definition
Maintain "organized patches" within membranes where proteins can consistently interact.
Patches of cholesterol and sphingomyelin exhibit higher transition temperatures to shift from "liquid, organized" states to "liquid, disorganized" states (cholesterol usually localizes to the outside of the raft). |
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Term
| What happens when the endoplasmic leaflets of RBCs shift to to become part of the exoplasmic face of the lipid bilayer? |
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Definition
Signals destruction by macrophages.
This happens during aging. Normally, (-) charged head groups of PS and PI on the endoplasmic leaflets of membranes anchor (+) charged tails of transmembrane proteins responsible for maintaining biconcave shape. If they shift to the exoplasmic face, they serve as signals for disposal. |
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Term
| True:False When integral membrane proteins flip-flop to opposite membrane orientations, they bind a distinct set of ligands. |
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Definition
False!
integral membrane proteins DO NOT FLIP FLOP |
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Term
| Provide 4 examples of how membrane proteins can be anchored? |
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Definition
1) Lipid anchors such as GPI anchors for the exoplasmic leaflet (glycocalyx proteins in SI) and fatty-acid anchors in the cytoplasmic leaflet (AFR in vesicular budding)
2) Lipid raft anchors- cholesterol molecules on edges of rafts surround proteins and prevent interactions
3) Multimeric Complexes- Bacterial photosynthetic reaction center
4) PDZ domains (80-90 AA in cytosolic proteins that anchor them to transmembrane proteins)- serve to cluster ion channels and signaling proteins at cellular junctions.
Example is CFTR in CF |
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