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Fat Review - Lipids Q&A
1. What are the main types of lipids? The main types of lipids are triglycerides (fats and oils), phospholipids, waxes and steroids. 2. What is the structural formula of glycerol? To which organic function do these molecules belong? Glycerol is a linear chain of three carbons; the central carbon is bound to one hydroxyl radical and to one hydrogen and the two other carbons in the extremities are bound to a hydroxyl radical and to two hydrogens. Spatial sides of the hydroxyls are the same. Lipids and Fat Review - Image Diversity: glycerol molecule 3. How are triglycerides made? Triglycerides, fats or oils, are made of three molecules of fatty acids bound to one molecule of glycerol. Hydroxyls of each one of the three fatty acids and each hydrogen of the hydroxyls of the glycerol bind to form three molecules of water that are liberated. Lipids and Fat Review - Image Diversity: triglyceride molecule 4. What are phospholipids? Phospholipids are molecules made of glycerol bound to two long molecules of fatty acids and to one phosphate group. Therefore, phospholipids are amphipathic molecules, i.e., they have a non-polar portion, due to the long fatty acid chains, and a polar portion, due to the group phosphate. Phospholipids are the main component of cell membranes. Sphingomyelin, the substance that forms the myelin sheath of axons in the nervous system, is a phospholipid too. Lipids and Fat Review - Image Diversity: phospholipid molecule 5. What are steroids? What are some examples of steroids with a biological function? Steroids are lipids based in an angular combination of four carbon rings, three of them made of six carbons and one ring made of five carbons in the extremity. The union of each ring to the adjacent ring is made by the sharing of two adjacent carbons belonging to both rings. Bile salts, cholesterol, the sexual hormones estrogen, progesterone and testosterone, the corticosteroids and the pro-vitamin D are examples of steroids. Lipids and Fat Review - Image Diversity: steroid structure 6. What are hydrophobic molecules (or hydrophobic molecular regions)? What are hydrophilic molecules? How can they be characterized in relation to their polarity? Hydrophobic molecules are those that have little or no propensity to dissolve in water (hydro = water, phobia = fear). Hydrophilic molecules are those that have great propensity to dissolve in water (philia = friendship). Water is a polar substance. Remembering the rule that “equal dissolves equal” one can conclude that hydrophobic substances are non-polar molecules while hydrophilic molecules are polar molecules. 7. Are organic solvents like benzene and ether polar or non-polar substances? Benzene and the ethers are molecules without electrically charged portions and thus they are non-polar substances. 8. Regarding solubility, how are lipids classified? Fats and oils are hydrophobic molecules, i.e., they are non polar and insoluble in water. Lipids in general are molecules with a large non-polar extension and so they are soluble in non polar solvents, like benzene, ether and chloroform. There are some amphipathic lipids, i.e., lipids whose molecules have a hydrophilic portion, like the phospholipids, giving them the property of being dragged by water, and a hydrophobic portion (non polar). 9. What is meant by saturation or unsaturation of oils and fats? When it is said that a triglyceride is saturated it means that in its molecule the carbon chain is bound in its maximum capacity to hydrogens, i.e., there are no double or triple bonds between carbons. These saturated molecules are generally solid fats at normal temperature. Unsaturated triglyceride molecules are those in which there are double or triple bonds between carbons and so they do not accomplish their maximum capacity of hydrogenation. These unsaturated molecules in general are oils, liquid at normal temperature. The terms saturated or unsaturated refer then to the saturation of the carbonic chain by hydrogen atoms. Lipids and Fat Review - Image Diversity: saturated fatty acid unsaturated fatty acid 10. Why do fats have thermal isolation properties? Triglycerides are weak heat conductors and in addition they form thick layers of fat tissue when accumulated by the organism. That is why they are good thermal isolators. In animals that live in cold climates, like polar bears, seals and whales, the adipose tissue helps the maintenance of the internal body temperature. 11. How are lipids used as an energy source by the organism? Carbohydrates are the main energy source for aerobic cell respiration. In the absence or deficiency of such substances the organism can use lipid stores since fats (like proteins) can be degraded into acetyl-CoA to feed the Krebs cycle (a stage of the aerobic cellular respiration). |