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Name: Section: Worksheet – ANSWER KEY Synthesis / Reflection-Guided Generalization 3 – Carbon Compounds (Biomolecules) COMPETENCY: S9MT-IIh-18. (MELC). Recognize the general classes and use of organic compounds. “Lipids” Lipids include fats, oils, waxes, phospholipids, and steroids. Lipids are hydrophobic, or insoluble in water, because they are nonpolar molecules. This is because they are hydrocarbons that include only nonpolar carbon-carbon or carbon-hydrogen bonds. A fat molecule, such as a triglyceride, consists of two main components—glycerol and fatty acids. Glycerol is an organic compound with three carbon atoms, five hydrogen atoms, and three hydroxyl (–OH) groups. Fatty acids have a long chain of hydrocarbons to which an acidic carboxyl group (-COOH) is attached, hence the name “fatty acid.” The number of carbons in the fatty acid commonly range from 12–18 carbons. The fatty acid is covalently bonded to each of the three oxygen atoms in the – OH groups of glycerol. Fatty acids may be saturated or unsaturated. If there are only single bonds in its hydrocarbon chain, the fatty acid is saturated. Saturated fats tend to get packed tightly and are solid at room temperature. Animal fats with stearic acid and palmitic acid contained in meat, and the fat with butyric acid contained in butter, are examples of saturated fats. Mammals store fats for long-term use, in specialized cells called adipocytes. In plants, fat or oil is stored in seeds, and is used as a source of energy during embryonic development. When the hydrocarbon chain contains a double bond, the fatty acid is unsaturated. Most unsaturated fats are liquid at room temperature and are called oils. The double bond causes a bend or a “kink” that prevents the fatty acids from packing tightly, keeping them liquid at room temperature. Olive oil, corn oil, canola oil, and cod liver oil are examples of unsaturated fats. Unsaturated fats help to improve blood cholesterol levels, whereas saturated fats contribute to plaque formation in the arteries, increasing the risk of a heart attack. A bilayer of phospholipids is the major constituent of the plasma membrane. In a phospholipid, two fatty acid chains and a phosphate group modified by the addition of an alcohol, are attached to a glycerol or similar backbone. In cells, the hydrophobic (i.e. “water-hating”) fatty acids of phospholipids in the plasma membrane
face inside, away from water, whereas the hydrophilic (“water-loving”) phosphate group can face either the outside environment or the inside of the cell, which are both aqueous. Waxes are made up of a hydrocarbon chain with an alcohol (–OH) group and a fatty acid. Examples of animal waxes include beeswax and lanolin. In plants, the wax coating of leaves helps prevent them from drying out. Although they do not resemble other lipids, steroids are grouped with them because they are also hydrophobic. All steroids have four, linked carbon rings and several of them, like cholesterol, have a short tail. Cholesterol is the precursor of many steroid hormones, such as testosterone and estradiol, and also the precursor of bile salts, which help in the breakdown of fats and their subsequent absorption by cells. Although cholesterol is often spoken of in negative terms, it is necessary for the proper functioning of the body. Article extracted and modified from: Malmquist, S. (n.d.). 4.1 Biological Molecules – Human Biology. Pressbooks. Retrieved October 5, 2022, from https://open.lib.umn.edu/humanbiology/chapter/4- 1 - biological- molecules/#:%7E:text=There%20are%20four%20major%20classes,majority%20of%20a%20cell’s%20mass. Questions
1. Why is a lipid mainly hydrophobic? Use the structure of the triglyceride or phospholipid to explain. ( 3 points) A lipid is mainly hydrophobic because it is a nonpolar hydrocarbon molecule, that includes mainly chains of nonpolar carbon-carbon or carbon-hydrogen bonds. In the structure of the triglyceride shown, there are 3 chains of 10-Carbon hydrocarbons made up of nonpolar C-C and C-H segments covalently bonded, that are linked to the glycerol molecule at the carboxyl-group end. In the structure of the phospholipid shown, there are 2 chains of 18-Carbon hydrocarbons made up of nonpolar C-C and C-H segments covalently bonded, that are linked to two carbons of a glycerol molecule. 2. “Saturated fats contribute to plaque formation in the arteries, which increases the risk of a heart attack.” What property and structural feature of saturated fats is responsible for this? (3 points) Only single bonds are present in the hydrocarbon chain of saturated fatty acids making up saturated fats. As a result, saturated fats tend to get packed tightly together (i.e. higher density), and are solid at room temperature. When present in the blood, saturated fats that easily solidify, may form deposits (plaques) that collect on artery walls, leading to an increased risk of a heart attack. 3. How are the diversity of lipids made possible? Use CER to answer. (4 points) The diversity of lipids can be seen in the variety of lipid structures. The structural variety is made possible by the ability of carbon to form multiple covalent bonds with itself, resulting in: single and double bonds between carbon atoms (e.g. saturated vs. unsaturated fatty acids); short or long linear and branched chains (e.g. fatty acids); or forming rings (e.g. steroids). Carbon also forms covalent bonds with other atoms (e.g. to hydrogen; or, to the oxygen of a hydroxyl (OH-) in fatty acids, or phosphate group in phospholipids) that are part of functional groups which help determine the reactivity, hydrophobicity or hydrophilicity of lipids.
