Concepts in Biochemistry

Concepts in Biochemistry

Scott M. Tremain, PhD

Student Learning Outcomes

Upon completion of this chapter, the student will be able to achieve the following outcomes:

• Explain the role of biochemistry in dental hygiene and nutrition.

• Assign biomolecules according to functional group.

• Compare and contrast the structure, function, and properties of the four major classes of biomolecules (carbohydrates, proteins, nucleic acids, and lipids).

• Outline the structure, function, and property of monosaccharides, disaccharides, and polysaccharides.

• Outline the structure, function, and property of amino acids and proteins.

• Compare and contrast the roles of enzymes, coenzymes, and vitamins in nutrition.

• Outline the structure, function, and property of nucleotides and nucleic acids.

• Outline the structure, function, and property of fatty acids, triglycerides, and steroids.

• Differentiate catabolism from anabolism. Explain connections between metabolic pathways in carbohydrate, protein, and lipid metabolism.

Key Terms

image Test Your NQ

1. T/F A hydrolysis reaction produces water as a product, while a condensation reaction requires water as a reactant.

2. T/F Nucleotides are the building blocks of proteins.

3. T/F Hydrophilic molecules dissolve readily in water.

4. T/F Sucrose is a disaccharide containing glucose and galactose.

5. T/F A substrate binds the enzyme active site and is converted into product.

6. T/F When the hydrogen atoms are on opposite sides of the double bond, the structure is a trans isomer.

7. T/F An unsaturated fatty acid with 16 carbons has a lower melting temperature than a saturated fatty acid with 16 carbons.

8. T/F Catabolism involves the reduction of carbohydrates into carbon dioxide and water.

9. T/F Insulin activates glycogen degradation to regulate carbohydrate and lipid metabolism.

10. T/F Humans lack the enzymes to synthesize essential (indispensable) amino acids, so they must be obtained from foods.

It is essential for dental professionals to have a basic understanding of biochemistry because it is the foundation for understanding and applying the concepts of nutrition. An overview of the biochemical concepts relevant to nutrition will serve as a wonderful resource as the learner goes through this textbook. A comprehensive review of chemistry and biochemistry concepts can be found online at Evolve.

What is Biochemistry?

Biochemistry is the study of life at the molecular level. The three major areas of biochemistry are structure, metabolism, and information. Structure describes the three-dimensional arrangement of atoms in a molecule, the smallest particle of a substance that retains all the properties of the substance. Important for life, the structure of a biomolecule determines its function. A biomolecule is any molecule that is produced by a living cell or organism, which would include carbohydrates, proteins, nucleic acids, and lipids, as well as other organic compounds found in living organisms; in contrast, a nutrient is a substance required by the body that must be supplied by an outside source which is usually food. Metabolism involves the production and use of energy. In metabolism, energy can be extracted from dietary carbohydrates, proteins, and lipids and used to create the biomolecules required for life. This highly regulated system ensures that energy is not wasted. Information involves the transfer of biological information from deoxyribonucleic acid (DNA) to ribonucleic acid (RNA) to protein. The blueprint for life is stored in DNA and the resulting proteins carry out all the processes required for life.

Fundamentals of Biochemistry

Atoms in a compound are held together by chemical bonds. There are two types of chemical bonds that form. An ionic bond forms between a positively charged metal ion and a negatively charged nonmetal ion. Hydroxyapatite in tooth enamel is composed of ionic bonds between calcium ions (Ca2+), phosphate ions (PO43−), and hydroxide ions (OH−). A covalent bond forms when electrons are equally shared between two nonmetals. Ultimately, the biomolecules responsible for life are based on carbon (C) because of carbon’s ability to form stable covalent bonds to itself and many other atoms, forming long chains and rings. In addition to carbon, the combination of different atoms, like hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P), into biomolecules provides for great variety in chemical structure, properties and reactivity in biological systems. One way to organize this variety in chemical structure is the classification of molecules into functional groups. A functional group is a group of atoms that gives a family of molecules its characteristic chemical and physical properties. Molecules that have similar functional groups have similar properties. Figure 2-1 defines and exemplifies a few functional groups found in biochemistry.

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FIGURE 2-1 Common functional groups in biochemistry.

Functional groups can be converted into other functional groups via chemical reactions such as oxidation-reduction, condensation, and hydrolysis. Oxidation-reduction reactions are important in metabolism as biomolecules are degraded or synthesized. Oxidation can be defined as a loss of electrons, an increase in charge, a gain of O atoms, or a loss of H atoms. Reduction can be defined as a gain of electrons, a decrease in charge, a loss of O atoms, or a gain of H atoms. In metabolism, energy is extracted from glucose (C6H12O6) by completely oxidizing it to carbon dioxide (CO2). Condensation and hydrolysis reactions are important in digestion and metabolism. In general, a condensation reaction creates a new molecule by forming a bond between two smaller molecules, while a hydrolysis reaction breaks a larger molecule into two smaller molecules. When carbohydrates, proteins, and lipids are digested, these biomolecules are hydrolyzed into smaller building blocks for absorption in the digestive system.

Principle Biomolecules in Nutrition

As shown in Table 2-1, the four major classes of biomolecules are carbohydrates, proteins, nucleic acids, and lipids. These biomolecules are characterized by the type of polymer, and monomer they contain as well as by their general function. A polymer is a large molecule containing numerous repeating units called monomers. A monomer is the smallest repeating unit present in a polymer.

Table 2-1

The four major classes of biomolecules

Polymer Monomer Function
Carbohydrates (polysaccharides) Amino acids Structure and biocatalysts (enzymes)
Proteins Monosaccharides Energy source, energy storage form and structure
Nucleic acids Energy source, energy storage form, and biological membranes
Lipids Nucleotides Genetic information transfer and energy

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Carbohydrate Structure and Function

The biological function of carbohydrates involves energy metabolism and storage. As shown in Figure 2-2, plants use photosynthesis to make oxygen (O2) and glucose (C6H12O6), the carbohydrate from which animals acquire the energy required for life. Via the process of respiration, animals degrade the carbohydrate glucose (C6H12O6) into CO2 and water (H2O), and plants use these products for photosynthesis.

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FIGURE 2-2 The carbon cycle. Plants utilize photosynthesis (use solar energy) to produce glucose (C6H12O6) and oxygen (from left to right), while animals utilize respiration to degrade glucose (C6H12O6) for energy (from right to left).

Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides, depending on the number of sugar monomers present (one, two, or many). Monosaccharides are composed of a single monomeric unit with the molecular formula Cn(H2O)n, where n is 3 to 8. Figure 2-3 shows the linear structures of the most common monosaccharides. Monosaccharides undergo oxidation-reduction reactions. When a monosaccharide is reduced, the aldehyde functional group changes to a sugar alcohol (e.g., sorbitol).

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FIGURE 2-3 The linear structures of common monosaccharides. Monosaccharides are classified as aldoses and ketoses. Aldoses contain an aldehyde functional group, while ketoses contain a ketone functional group. D-glucose (C6H12O6) is an aldohexose because it contains an aldehyde (represented by CHO at carbon 1) and six carbons. D-Fructose (C6H12O6) is a ketohexose because it contains a ketone (at carbon 2) and six carbons.

In aqueous solution, linear monosaccharides spontaneously form cyclic structures. When two monosaccharides combine, a disaccharide is formed. This involves the formation of a glycosidic bond. As shown in Figure 2-4, two glucose monomers can combine via a condensation reaction to form maltose. Maltose is a disaccharide that results from the degradation of starch and is used in brewing alcoholic beverages. When glucose and fructose combine, the disaccharide sucrose is formed (Figure 2-5). This disaccharide is table sugar and one of the sweetest carbohydrates. When the two monosaccharides galactose and glucose combine, the disaccharide lactose is formed (Figure 2-5). This disaccharide is found in milk and dairy products.

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FIGURE 2-4 Formation of the disaccharide maltose from two glucose molecules. Water (H2O) is released as a product in this condensation reaction.
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FIGURE 2-5 The structures of the disaccharides sucrose and lactose.

Many monosaccharides combine to form a polysaccharide. As shown in Table 2-2, polysaccharides can be characterized by the monosaccharide monomer present and overall function. One of the most important dietary polysaccharides is starch, the storage form of energy in plants. Starch is composed of two different polysaccharides (α-amylose and amylopectin). Figure 2-6 shows the linear structure of the polysaccharide α-amylose. Figure 2-7 shows the branched structure of the polysaccharide amylopectin. Important for the storage of energy in animals, glycogen also is a branched polysaccharide containing glucose monomers. The highly branched structure of glycogen allows its rapid degradation into glucose when energy is needed.

Table 2-2

Summary of common polysaccharides

Name Monomer Biological Function
Amylose (in starch) Glucose Nutrient storage (plants)
Amylopectin (in starch) Glucose Nutrient storage (plants)
Glycogen Glucose Nutrient storage (animals)
Dextran Glucose Nutrient storage (yeast and bacteria)
Inulin Fructose Nutrient storage (plants)
Cellulose Glucose Structure in plants
Pectin Galacturonic acid Structural rigidity in plants and gelling agent in yogurt and jelly
Lignin Coniferyl alcohol Structural rigidity in plant cell walls
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FIGURE 2-6 The linear structure of the polysaccharide α-amylose, a component of starch containing glycosidic linkages that are easily digested. (From Batmanian L, Worrall S, Ridge J: Biochemistry for health professionals, Chatswood, NSW Australia, 2012, Mosby.)
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FIGURE 2-7 The branched structures of the polysaccharides amylopectin and glycogen. Amylopectin is a component of starch (the storage form of energy in plants) containing glucose monomers. Glycogen is the storage form of energy in animals containing glucose monomers. (From Batmanian L, Worrall S, Ridge J: Biochemistry for health professionals

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Feb 12, 2015 | Posted by in Dental Hygiene | Comments Off on Concepts in Biochemistry

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