Science, Part 34
Question 1: Discuss important processes and reactions associated with carbohydrates.
Answer 1: Carbohydrates are important organic molecules containing carbon, hydrogen, and oxygen; they are the primary source of energy for most living organisms. Carbohydrate digestion is the result of several fundamental metabolic pathways and each process involves a great many subsidiary reactions. The formation of glucose from carbohydrates is one important pathway. Glucose (C6H12O6) is one of several monosaccharides produced from carbohydrates by chemical reactions. Glucose molecules then enter another metabolic pathway called glycolysis in which they are broken down into pyruvate (C3H4O3), which in turn begins another series of cascading reactions which lead to usable energy. The citric acid cycle is another important metabolic pathway in the digestion of carbohydrates.
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Question 2: Discuss important processes and reactions associated with lipids.
Answer 2: Lipids are biomolecules that are insoluble in water but soluble in other nonpolar solvents. They are responsible for the waxy or greasy nature of substances found in plants and animals. Saponification is a process used to further distinguish classes of lipids; it is the process by which esters are hydrolyzed in base solution to yield glycerol and the salts of fatty acids. If lipids do not contain esters, they are nonsaponifiable and are classified accordingly. Hydrolysis is another important reaction for lipids. In the presence of water and an acid catalyst, lipids break down into glycerol and fatty acids. Hydrogenation is the process of converting C=H double bonds to C—H single bonds resulting in increased saturation of the hydrocarbon and a correspondingly higher melting point.
Question 3: Discuss important processes and reactions associated with proteins.
Answer 3: Proteins can also be metabolized for use as a source of energy, but this is merely one catabolic pathway associated with them. Because proteins are constructed of long chains of amino acids, reactions early in the process are of particular interest. One is the oxidation of cysteine, a sulfur-containing amino acid. Two cysteine molecules combine with oxygen and fuse to form a S—S disulfide bond, creating one molecule of cystine. This reaction is important in determining the unique structure of some proteins. Peptides are groups of two or more linked amino acids. Peptide formation occurs during protein synthesis when a carboxyl group reacts with an amine of a second amino acid to release water and form an amide bond which links the two amino acids into a peptide. The amide bond is called a peptide bond; many such reactions can produce long chains (polypeptides) that eventually become proteins.
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