Lipid Classifications - Biochemistry

In a saturated fatty acid, all of the covalent carbon to carbon bonds are single bonds. So a carbon atom in the middle of the chain will have two covalent bonds to other carbon atoms, and can therefore bond to two hydrogen atoms.

Double bonds cause unsaturation, thus decreases the melting point. Cis-double bonds as well as methylation also introduce kinks within the chain, decreasing the melting point. Increasing the fatty acid chain length creates saturation, thus causes the melting point to increase. Therefore, decreasing fatty acid chain length has the adverse effect.

Alpha-linolenic acid is an essential fatty acid that must be consumed in the diet (cannot be synthesized by the body). It is an eighteen-carbon omega-3 fatty acid that is used to synthesize eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two important long chain polyunsaturated fatty acids. Alpha-linoleic acid is the precursor to arachodonic acid (AA).

Omega-6 fatty acids are primarily found in vegetable oils (ex. soybean oil or corn oil), chicken, and eggs. Note that poultry feed is very heavy on corn products and thus increases the omega-6 fatty acid proportion of almost all farm raised animals. Fish, chia seeds, and flax seeds are high in omega-3 fatty acids.

Dihomo-gamma-linolenic acid (DGLA) is a twenty-carbon omega-6 fatty acid that is a desaturation product of linoleic acid. The rest of the answer choices are indeed omega-3 fatty acids.

Omega-3 fatty acids can be utilized as a substrate for the synthesis of series 3 prostaglandins (a subclass of eicosanoids), and are generally considered "anti-inflammatory" for this reason. Furthermore, omega-3 fatty acids are so named for having a double bond at the 3rd carbon from the omega end. They are generally found in fish and flax and chia seeds, while omega-6 fatty acids are in poultry and vegetable oils.

Arachidonic acid (AA) is used as a substrate for series 2 eicosanoid synthesis, including thromboxane A2 (TXA2). Series 3 eicosanoids are synthesized from alpha-linolenic acid (ALA), and series 1 are synthesized from dihomo-gamma-linolenic acid (DGLA).

Alpha-linolenic acid (ALA) is an omega-3 fatty acid that is utilized to produce series 3 eicosanoids. Series 3 eicosanoids lead to a weak platelet aggregation response, and are considered anti or less-inflammatory. Thus, a diet rich in omega-3 fatty acids is recommended for those with heart disease risk. Omega-3 fatty acids are primarily found in fish or flax and chia seeds, not vegetable oil, which is rich in omega-6 fatty acids.

The hydrocarbon tail of free fatty acids is nonpolar, and so it interacts unfavorably with water molecules. So, when free fatty acids are placed in a polar environment, the nonpolar tails are driven together and inward in order to avoid water molecules. A micelle is formed from the circular formation of free fatty acids.

A greater degree of unsaturation results in a disruption of van der Waals forces between fatty acid chains. This is due to the "kinks" that occur within an unsaturated fatty acid. It is easy to visualize a fatty acid membrane with kinks being less tightly packed, and therefore more fluid. This increase in fluidity is independent of temperature.

The rules for fatty acid nomenclature state that Omega 6 means that a double bond is located at the sixth position of the fatty acid - counting from the methyl end.

Linoleic acid's nomenclature is C18:29,12. Linolenic acid's nomenclature is C18:39,12,15. They both have 18 carbons but differ by one extra double bond in linolenic acid.

Glycerol phosphate can be created by the glycerol phosphate shuttle. Insects use this process in their muscles for flying, because they require quick ATP synthesis. To generate that ATP, the NADH synthesized during glycolysis ends up being regenerated into , and is shuttled over to the mitochondria to participate immediately in oxidative phosphorylation. Via the glycerol phosphate shuttle, NADH reduces dihydroxyacetone phosphate directly into glycerol phosphate, in a reaction that is catalyzed by glycerol 3-phosphate dehydrogenase. The metabolite here that can be recognized from glycolysis is the dihydroxyacetone phosphate. Phosphoenolpyruvate, pyruvate, and 3-phosphoglycerate are all indeed glycolysis metabolites, but none could be easily reduced to glycerol 3-phosphate. If you guessed glyceraldehyde 3-phosphate, you’d be close, because structurally, it appears that it could also be directly reduced to glycerol phosphate. Indeed, during glycolysis, it is interconverted to dihydroxyacetone phosphate. But the glycerol phosphate shuttle uses dihydroxyacetone phosphate; hence, the answer is dihydroxyacetone phosphate.

Cholesterol is made up of multiple rings, including three six-carbon rings and one five-carbon ring. This characteristic structure is also seen in steroid hormones and metabolites, as many biologically relevant molecules are derived from cholesterol. Fatty acids are long hydrocarbons (typically between ten and thirty carbons long) with carboxylic acid functional groups on one end. Glycolipids are lipids that have carbohydrate moieties attached, which play a role in cellular and molecular communication. Sphingolipids are a class of lipids that contain a sphingoid base backbone and include sphingosine, sphingomyelin, ceramides, gangliosides and others.

The prefix "glyco-" means "sugar." Glycolipids are thus lipids that have a sugar component. Glycolipids containing sphingoid bases are called sphingolipids. Glycolipids containing phosphate are called phospholipids. Lipoproteins are molecules that contain both lipid and peptide components.

Terpenoids (also called isoprenoids) are produced mostly by plants. Many vitamins such as A, E, and K are terpenoids, and steroids/sterols also belong to this group.

Only "HDL is a dense lipoprotein that carries cholesterol from the body to the liver" is a true statement. Chylomicrons are the largest and least dense lipoprotein, and they carry dietary lipids. VLDL carries lipids synthesized in the liver to the body. they are more dense the chylomicrons. LDL carries cholesterol around the body, and HDL is the most dense and carries cholesterol to the liver for breakdown.

Phospholipids are amphipathic, meaning they have an end that is hydrophobic (the fatty acid tail) and an end that is hydrophilic (the head). Phosphate groups have a negative charge, thus attracting them to water, and the presence of a phosphate group at the head of a phospholipid makes that head hydrophilic. Glycerol itself polarizes a fatty acid, but the glycerol is located in the head, not the backbone, and is not charged like phosphate.

The polar head groups and the hydrocarbon tails will separate themselves in such a way that one-tailed phospholipids will form micelles, whereas two-tailed phospholipids will form a bilayer (liposome).