Chapter 1. Chemistry of Life - Advanced TABLE 1.2: title

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1 Condensation and Hydrolysis Condensation reactions are the chemical processes by which large organic compounds are synthesized from their monomeric units. Hydrolysis reactions are the reverse process. During condensation reactions, water is produced from the two molecules being bonded together; an H from one monomer is joined to an -OH from another molecule, producing H 2 O. TABLE 1.2: title Polymer Monomer Bond carbohydrates monosaccharides glycosidic lipids fatty acid ester* proteins amino acids peptide nucleic acids nucleotides phosphodiester** The ester linkage is between a glycerol molecule and fatty acid chain. See for additional information. Vocabulary adenosine triphosphate (ATP): Energy-carrying molecule that cells use to power their metabolic processes; energy-currency of the cell. amino acid: Small molecule that is a building block of proteins; the monomer of a polypeptide. carbohydrate: Organic compound such as sugar or starch; major source of energy to living cells. condensation reaction: A chemical reaction in which two molecules combine to form one single molecule, together with the loss of a small molecule, often water. functional group: Part of organic compound that generally determines the nature and functions of the compound. hydrolysis reaction: A chemical process in which a molecule of water is split, resulting in the separation of a large molecule into two smaller molecules. lipid: Organic compound such as fat or oil. macromolecule: A large molecule composed of individual monomer units. nucleic acid: Organic compound such as DNA or RNA. nucleotide: Monomer of nucleic acids, composed of a nitrogen-containing base, a five-carbon sugar, and a phosphate group. organic compound: Compound found in living organisms; contains mainly carbon. protein: Organic compound made of amino acids. Summary Carbon s exceptional ability to form bonds with other elements and with itself allows it to form a huge number of large, complex molecules called organic molecules. These molecules make up organisms and carry out life processes. Practice Use this resource to answer the questions that follow. Biology for AP* Search: Organic Molecules: Overview 11

2 1.2. The Significance of Carbon - Advanced 1. What is an organic compound? 2. Describe the element carbon. 3. What is the chemical composition of aspirin? Is it a natural or synthetic compound? Explain your answer. 4. Describe organic reactions. Also see the following for additional related information. Biology for AP* Search: Elements of Life Biology for AP* Search: Organic Chemistry Review 1. Why is carbon essential to all known life on Earth? 2. What is an organic compound? Give an example. 3. List the four main classes of organic compounds. What are examples of each? 4. What is condensation of hydrolysis? 5. What is a phosphodiester bond? 12

3 1.3 Carbohydrates - Advanced Describe the structure and function of carbohydrates. Sugar. Does this look like biological energy? As a child, you may have been told that sugar is bad for you. Well, that s not exactly true. Essentially, carbohydrates are made of sugar, from a single sugar molecule to thousands of sugar molecules all attached together. Why? One reason is to store energy. But that does not mean you should eat it by the spoonful. Carbohydrates Carbohydrates are organic compounds that contain only carbon (C), hydrogen (H), and oxygen (O). They are the most common of the four major types of organic compounds. There are thousands of different carbohydrates, but they all consist of one or more smaller units called monosaccharides. Monosaccharides and Disaccharides The general formula for a monosaccharide is: (CH 2 O) n, where n can be any number greater than two. For example, if n is 6, then the formula can be written: C 6 H 12 O 6. This is the formula for the monosaccharide glucose. Another monosaccharide, fructose, has the same chemical formula as glucose, but the atoms are arranged differently. Molecules with the same chemical formula but with atoms in a different arrangement are called isomers. Compare the glucose and fructose molecules in Figure

4 1.3. Carbohydrates - Advanced Can you identify their differences? The only differences are the positions of some of the atoms. These differences affect the properties of the two monosaccharides. Monosaccharides can be classified by the number of carbon atoms they contain: diose (2), triose (3), tetrose (4), pentose (5), hexose (6), heptose (7), and so on. In addition to glucose, other common monosaccharides include fructose ("fruit sugar"), galactose, xylose ("wood sugar") and ribose (in RNA) and deoxyribose (in DNA). If two monosaccharides bond together, they form a carbohydrate called a disaccharide. Two monosaccharides will bond together through a dehydration reaction, in which a water molecule is lost. A dehydration reaction is a condensation reaction, a chemical reaction in which two molecules combine to form one single molecule, losing a small molecule in the process. In the dehydration reaction, this small molecule is water. An example of a disaccharide is sucrose (table sugar), which consists of the monosaccharides glucose and fructose (Figure 1.5). Other common disaccharides include lactose ("milk sugar") and maltose. Monosaccharides and disaccharides are also called simple sugars. They provide the major source of energy to living cells. FIGURE 1.5 Sucrose Molecule. This sucrose molecule is a disaccharide. It is made up of two monosaccharides: glucose on the left and fructose on the right. Sucrose forms through a condensation reaction: glucose (C 6 H 12 O 6 ) + fructose (C 6 H 12 O 6 ) sucrose (C 12 H 22 O 11 ). Oligosaccharides An oligosaccharide is a saccharide polymer containing a small number (typically two to ten) of monosaccharides. Oligosaccharides can have many functions; for example, they are commonly found on the plasma membrane of animal cells where they can play a role in cell cell recognition. In general, they are found attached to compatible amino acid side-chains in proteins or to lipids. Oligosaccharides are often found as a component of glycoproteins or glycolipids. They are often used as chemical markers on the outside of cells, often for cell recognition. An example is ABO blood type specificity. A and B blood types have two different oligosaccharide glycolipids embedded in the cell membranes of the red blood cells, AB-type blood has both, while O blood type has neither. Polysaccharides Polysaccharides are long carbohydrate molecules of repeated monomer units joined together by glycosidic bonds. A polysaccharide may contain anywhere from a few monosaccharides to several thousand monosaccharides. Polysaccharides are also called complex carbohydrates. Polysaccharides have a general formula of C x (H2O) y, where x is 14

5 usually a large number between 200 and Considering that the repeating units in the polymer backbone are often six-carbon monosaccharides, the general formula can also be represented as (C 6 H 10 O 5 ) n, where 40 n Starches are one of the more common polysaccharides. Starch is made up of a mixture of amylose (15 20%) and amylopectin (80 85%). Amylose consists of a linear chain of several hundred glucose molecules and amylopectin is a branched molecule made of several thousand glucose units. Starches can be digested by hydrolysis reactions, catalyzed by enzymes called amylases, which can break the glycosidic bonds. Humans and other animals have amylases, so they can digest starches. Potato, rice, wheat, and maize are major sources of starch in the human diet. The formations of starches are the ways that plants store glucose. Glycogen is sometimes referred to as animal starch. Glycogen is used for long-term energy storage in animal cells. Glycogen is made primarily by the liver and the muscles. The main functions of polysaccharides are to store energy and form structural tissues. Examples of several other polysaccharides and their roles are listed in the Table 1.3. These complex carbohydrates play important roles in living organisms. TABLE 1.3: Complex Carbohydrates Complex Carbohydrate Function Organism Starch Stores energy Plants Amylose Stores energy Plants Glycogen Stores energy Animals Cellulose Forms cell walls Plants Chitin Forms an exoskeleton Some animals 15