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Biochemistry Study Q's 1-10

OK, I'm going to write these out because it helps me remember.

1. What is the common property of lipids? Hydrophobicity. Why is the term amphipathic used to describe lipids, and why is this propery important in the bahvior of lipids in aqueous media? Amphipathic means having both hydrophobic and hydrophilic elements. Most lipids have at least one polar or hydrophilic part, which is what allows them to form micelles in watery solution, or to align properly in cell membranes.

2. Idenity the major classes of lipids and the kind of structure or activity in which each class is important.

Fatty acids - Any of a class of aliphatic monocarboxylic acids that form part of a lipid molecule and can be derived from fat by hydrolysis (e.g., oleic, palmitic, or stearic acids); fatty acids are simple molecules built around a series of carbon atoms linked together in a chain of 12 to 22 carbon atoms. Free ones are the preferred fuel of the heart, and can be taken from the blood by any tissue. They accumulate in disorders associated with peroxisomes.

Glycerides - with the glycerol backbone, an organic acid ester of glycerin, designated, according to the number of ester linkages, as a mono, di- or triglyceride.

Phosphoglycerides - Glycerol-based phospholipids, the main component of biological membranes. Acylglycerol and diacylglycerol phosphates;constituents of nerve tissue, and involved in fat transport and storage.

Spingolipids - Involved in membrane structure. A class of lipids derived from the aliphatic amino alcohol sphingosine. Sphingolipids are often found in neural tissue, esp the white matter of the brain, and play an important role in both signal transmission and cell recognition, and cell membrane structure. Derived from ceramide, based on sphingosine.

Ketone Bodies - An energy source derived from fatty acids, could be considered carbs. What the brain burns after a few days of fasting when glucose is depleted.

Cholesterol - A four ring hydrophobic sterol, a combination of steroid and alcohol. Most cholesterol is synthesized by the body and some has dietary origin. Cholesterol is more abundant in tissues which either synthesize more or have more abundant densely-packed membranes, for example, the liver, spinal cord and brain. Central to the composition of cell membranes and the synthesis of steroid hormones. Cholesterol is transported in the circulatory system bound to lipoproteins

Lipoproteins -- spherical particles which have an exterior composed mainly of water-soluble proteins. The main types, low-density lipoprotein (LDL) and high-density lipoprotein (HDL) carry cholesterol from and to the liver, respectively.

Steroid - a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion. Steroids vary by the functional groups attached to these rings and the oxidation state of the rings. Hundreds of distinct steroids are found in plants, animals, and fungi. All steroids are made in cells either from the sterol lanosterol (animals and fungi) or the sterol cycloartenol (plants). Both sterols are derived from the cyclization of the triterpene squalene.

Eicosanoids -- Signaling molecules made by oxygenation of twenty-carbon essential fatty acids, (EFAs). They exert complex control over many bodily systems, mainly in inflammation or immunity, and as messengers in the central nervous system. Eicosanoids derive from either omega-3 (ω-3) or omega-6 (ω-6) EFAs. The ω-6 eicosanoids are generally pro-inflammatory; ω-3's are much less so. The amounts and balance of these fats in a person's diet will affect the body's eicosanoid-controlled functions, with effects on cardiovascular disease, triglycerides, blood pressure, and arthritis. Anti-inflammatory drugs such as aspirin and other NSAIDs act by downregulating eicosanoid synthesis. There are four families of eicosanoids—the prostaglandins, prostacyclins, the thromboxanes and the leukotrienes. For each, there are two or three separate series, derived either from an ω-3 or ω-6 EFA. These series' different activities largely explain the health effects of ω-3 and ω-6 fats.

3. Provide a general definition of a fatty acid. What is meant by a saturated fatty acid? Define unsaturated and poly unsaturated fatty acids? What is the configuration of the double bond in naturally occurring unsaturated fatty acids?

A fatty acid is a simple molecule made of a long chain of carbon molecules (12-22 C's) that are either saturated (full of hydrogens, "-anoic acid") or unsaturated (with double bonds between carbons "-enoic acid") that has a COO- (carboxyl group) at one end, where it can link up with other things. Polyunsaturated means it has more than one double bond. Anywhere that a fatty acid is unsaturated, it is sensitive to oxidation. Hydrogenation of oils is the process of eliminating double bonds by sticking on hydrogens everywhere. In natural fatty acids, (almost) only CIS double bonds are found.

4. What is the relationship of fatty acid chain length to membrane fluidity and to melting point? What is the relationship of the dgree of fatty acid unsaturation to membrane fluidity and melting point?

The longer a saturated fatty acid chain is, the higher the melting point. The more unsaturated it is, the lower the melting point. WHAT ABOUT MEMBRANE FLUIDITY? I would guess that fluidity is directly related to melting point, because for a membrane to be fluid the fats need to be "melted".

5. Name the essential fatty acids. Why are they essential? Essential: linoleic and linolenic acid, both 18 carbons with 2 and 3 double bonds respectively. They're essential because we have no enzyme with which to make them, so we have to eat them.

6. What's the difference between triacylglycerols and triglycerides? There is none. Triglycerides is the old name, triacylglycerols is the new name. TG and TAG are alternative codes for these esters of glycerol and fatty acids. They are less dense than water, do not cause osmotic problems in the body, and are a concentrated form of energy for the body.

7. What are the 5 most prominent types of phosphoglycerides? Which group are called lecithins?

--phosphatidylcholine = lecithin, occurs in the mucosa of the large intestine, forming the mucosal barrier, protecting the large intestine from attacks from colonic commensal bacteria. Patients suffering from ulcerative colitis have a disturbed mucosal barrier, and the mucus layers in their large intestines exhibit lower levels of phosphatidylcholine than that of healthy people. Lecithin (esp as derived from soy) is used commercially in substances requiring a natural emulsifier and/or lubricant, from pharmaceuticals to protective coverings. For example, lecithin is the emulsifier that keeps cocoa and cocoa butter in a candy bar from separating.
--phosphatidylserine
--phosphatidyl ethanolamine
--phosphatidyleinositol
--cardiolipin = an important component (20% of lipids) in the inner mitochondrial membrane. Serves as an insulator and stabilizes the activity of protein complexes important to the electron transport chain. Cardiolipin is a "double" phospholipid because it has four fatty acid tails, instead of the usual two.

8. How do phosphoglycerides, sphingomyelins, glycosphingolipids and triglycerides differ? In what tissues are sphingolipids most prominent? What is the defect in sphingolipid metabolism that occurs at a high frequency in Jewish populations?

--phosphoglycerides = has both glycerol and phosphate group with head group attached. Main component of biological membranes, constituents of nerve tissue, and involved in fat transport and storage.

--sphingomyelin = a sphingophospholipid with a head group on the phosphate, one fatty acid chain, and springosine for the backbone and one long chain. Found in animal cell membranes, especially in the membranous myelin sheath which surrounds some nerve cell axons. It usually consists of phosphorylcholine and ceramide. In humans SPH represents ~85% of all sphingolipids.

--glycosphingolipids = a subtype of glycolipids with sphingosine for the backbone and one tail, no phosphate group, and a carbohydrate attached. Incl: cerebrosides, gangliosides, globosides, sphingomyelin. Found on the outer surface of all eukaryotic cell membranes.

--triglycerides = glycerolipid with a glycerol backbone and three fatty acid chains attached. Major component of VLDLs and chylomicrons, important in metabolism as energy source and transporter of dietary fat. Fat and liver cells can synthesize and store triglycerides. Glucagon signals the breakdown of the triglycerides by hormone-sensitive lipase to release free fatty acids. As the brain can not utilize fatty acids as an energy source, the glycerol component of triglycerides can be converted into glucose, via gluconeogenesis, for brain fuel.

The most common lipid metabolism deficiency in Jews is Tay Sachs disease, which is the lack of the enzyme B-Hexosaminidase A. It stops the degradation of sphingolipids early in the process, and causes the accumulation of gangliosides, rapid and progressive neurodegeneration, blindn ess, cherry-red macula, muscular weakness and seizures.

9. Be able to identiy fatty acids based on delta and omega naming conventions.

Delta number system counts the carboxy carbon as #1, while the Omega system counts the methyl group on the end of the fatty acid chain as carbon #1. Biochemists tend to use the delta system, while nutritionists prefer the omega system. Omega 3 and 6 fatty acids are numbered by nutritionists.

FATTY ACID SYNTHESIS

10. what does the acetyl-CoA shuttle accomplish? It transports two carbon units and reducing equivalents out of the mitochondria.

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