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Chapter 8 Lecture
Basic ChemistryFourth Edition
Chapter 8 Chemical Reactions8.5 Biochemical Compounds
Learning Goal Identify the type of a biochemical compound from its structure and name its functional groups. Proteins are found in foods such
as eggs, milk, meat, and fish as well as plants such as grains, beans, and nuts.
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Biochemical Compounds
Biochemical compounds are organic compounds that are found in living things. They are large molecules and include the following groups of compounds:
•carbohydrates
•lipids
•proteins
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Carbohydrates
Carbohydrates are a group of biochemical compounds and consist of monosaccharides, disaccharides, and polysaccharides.
Carbohydrates contained in foods such as pasta and bread provide energy for the body.
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Carbohydrates
• In plants, energy from the Sun converts carbon dioxide and water into the carbohydrate glucose, which can be made into long-chain polymers.
• Plants convert glucose into starch for energy storage and cellulose to build structure.
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Carbohydrates
Monosaccharides
Glucose, the most common monosaccharide, has an aldehyde group on the first carbon.
• are the simplest carbohydrates
• contain a chain of carbon atoms with several —OH groups as well as an aldehyde or ketone group
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Monosaccharides
Honey contains two monosaccharides: glucose, an aldehyde sugar, and fructose, a ketone sugar.
Honey is a mixture of fructose and glucose.
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Disaccharides, Polysaccharides
A disaccharide consists of two monosaccharide units joined together.
Table sugar is a disaccharide that contains one unit of glucose and one unit of fructose.
Polysaccharides are carbohydrates such as amylose and cellulose, which contain many units of glucose.
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Disaccharides, Polysaccharides
The most stable form of monosaccharides are six-atom rings, formed when the aldehyde or ketone group reacts with the hydroxyl group at the other end of the chain.
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Lipids
Lipids are
•a family of biochemical molecules
•only soluble in organic solvents, not in water
•important in cell membranes, fats, cholesterol, and steroid hormones
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Lipids, Fatty Acids
Fats and oils contain fatty acids, long chains of carbon atoms with a carboxylic acid at one end.
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Lipids, Fatty Acids
Saturated fatty acids, generally solids at room temperature, contain only single bonds between carbon atoms.
Unsaturated fatty acids, generally liquids at room temperature, have one or more double bonds between carbon atoms.
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Lipids, Fatty Acids
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Chemistry Link to Health
Vegetable oils contain omega-6 fatty acids in which the double bond occurs at the sixth carbon from the CH3— end.
Fatty acids in fish oils are mostly omega−3 type in which the double bond occurs at the third carbon from the CH3— end.
Omega-3 fatty acids reduce the amount of plaque that forms, blocking walls of the blood vessels.
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Chemistry Link to Health
Diets that contain fish provide higher amounts of omega-3 fatty acids and reduce the possibility of developing heart disease.
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Lipids, Triacylglycerols (Fats)
Triacylglycerols, fats or oils, have hydroxyl groups on the trialcohol glycerol that form ester bonds with the carboxyl groups of fatty acids.
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Lipids, Triacylglycerols (Fats)
Triacylglycerols are a major form of energy storage for animals.
Animals that hibernate eat large quantities of plants, seeds, and nuts, which contain high levels of fats and oils.
As animals hibernate, they use their stored fat as a source of energy.
Prior to hibernation, a polar bear eats food with a high content of fats and oils.
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Chemistry Link to Industry
There are two types of unsaturated fatty acids: those that contain a cis structure and those that contain a trans structure.
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Chemistry Link to Industry
Hydrogenation is the process of adding hydrogen atoms across a carbon-carbon double bond, converting the double bonds to single bonds.
As the unsaturated fats are converted to saturated fats, they become solids that can be used in margarines and shortenings.
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Chemistry Link to Industry
During hydrogenation not all the fats may have been hydrogenated, and some of the cis−bonds may be converted to trans−bonds, or trans fatty acids.
Trans fatty acids
•behave like saturated fatty acids in the body
•raise the levels of LDL-cholesterol that can accumulate in the arteries
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Chemistry Link to Industry
If labels on the margarine or shortening state that the oils have been “partially hydrogenated” or
“fully hydrogenated,”
that product will also
contain trans fatty acids.
In commercial hydrogenation, nickel is used to catalyze the hydrogenation of unsaturated fats in vegetable oils to produce solid products containing saturated fats.
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Proteins
Proteins
•are biologically active polymers
•consist of just 20 different amino acid building blocks which are repeated in different sequences
•can function as enzymes regulating metabolism and digestion
•can transport oxygen in the blood and muscle
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Amino Acids
Amino acids
• are the building blocks of proteins
• contain an amino (—NH2) group and a carboxylic acid (—COOH) group connected to a central (alpha) carbon atom
• differ from each other by the side chains attached to the central carbon atom
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Amino Acids
In biological systems, the amino and carboxylic groups are present in their ionic forms.
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Amino Acids
The structures, names, and three-letter abbreviations of some common amino acids are listed below:
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Peptides
Peptides are chains of amino acids joined by a peptide bond.
A peptide bond is formed when the —COO− group of one amino acid reacts with the H3N±− group of a second amino acid.
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Peptides
The dipeptide Gly−Ala is formed when glycine reacts with alanine, forming a peptide bond.
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Aspartame, Artificial Sweetener
Aspartame is made when aspartic acid reacts with the methyl ester of phenylalanine. The sweetener is 180 times sweeter than sucrose (table sugar).
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Learning Check
Label each of the following definitions with a biochemical molecule, carbohydrate, lipid, or protein.
A.a polymer of amino acids
B.a biochemical molecule that is not soluble in water
C.a polymer of monosaccharide units
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Solution
Label each of the following definitions with a biochemical molecule, carbohydrate, lipid, or protein.
A.a polymer of amino acidsprotein
B.a biochemical molecule that is not soluble in water lipid
C.a polymer of monosaccharide unitscarbohydrate
