1.4 Carbohydrates and Lipids PDF

Carbohydrates and Lipids 1.4 Although carbohydrates and lipids can be quite large, they are relatively simple bio- chemical molecules. They are composed mostly of carbon, hydrogen, and oxygen,...

Carbohydrates and Lipids 1.4 Although carbohydrates and lipids can be quite large, they are relatively simple bio- chemical molecules. They are composed mostly of carbon, hydrogen, and oxygen, arranged in a variety of configurations. Although simple in structure, however, they perform many complex functions in cells. Carbohydrates and lipids are best known for their role as energy sources in the body, yet they are much more than this (Figure 1). Carbohydrates play a role in structural support and cell-to-cell com- munication. They are the raw material that is used to build other important mol- ecules, such as amino acids, lipids, and nucleic acids. Lipids also play an important structural role in cells—all biological membranes are composed of lipid molecules. As well, hormones, certain vitamins, and defence mechanisms are based on lipids. Figure 1 Bees produce honey, a Lipids provide insulation for nerve cells and have waterproofing qualities. The func- carbohydrate, and store it in hives tional groups on carbohydrates and lipids influence their properties and functions. constructed from waxes, a type of lipid. CAREER LINK Carbohydrates Carbohydrates, or simple and complex sugar molecules, are among the most common carbohydrate a biomolecule that consists biological molecules on Earth. The term “carbohydrate” comes from the terms carbo, of carbon, oxygen, and hydrogen meaning carbon, and hydrate, meaning water. In photosynthesizing plants and other photosynthesizing organisms, carbon dioxide and water molecules are used as raw materials to build carbohydrates. Plants and algae produce millions of tonnes of carbohydrates each year. These and other organisms use carbohydrates as an energy source, as a building material, and for cell communication. Carbohydrates are in the foods you eat, including fruits, vegetables, and grains. Nutritionists study the com- position of food and determine the amounts of carbohydrates that are present in the different foods we eat. CAREER LINK Monosaccharides The simplest type of carbohydrate is called a monosaccharide, because it contains a monosaccharide the simplest form of single sugar. Monosaccharides generally have a combination of carbon, hydrogen, carbohydrate, consisting of a single sugar and oxygen atoms in the ratio of 1 carbon : 2 hydrogen : 1 oxygen. This is repre- unit; a building block for more complex sented by the chemical formula (CH2O)n, or its derivative CnH2nOn, where n is the carbohydrates number of carbon atoms. Carbohydrates appear either as monosaccharides or as two or more monosaccharide units linked together. Glucose is perhaps the most widely used monosaccharide. Plants produce glucose during photosynthesis, and it provides energy for countless functions in both plants and animals. Monosaccharides that contain three carbons (triose), five carbons (pentose), and six carbons (hexose) are the most common in living organisms (Figure 2(a), next page). Although all monosaccharides can occur in a linear form, when formed in water, monosaccharides with five or more carbon atoms fold back on themselves to form a ring. Folding into a ring occurs through a reaction between two functional groups in the same monosaccharide. This can be seen in the monosaccharide glucose, when the carbonyl group interacts with a hydroxyl group to form a ring (Figure 2(b), next page). Carbon atoms in the glucose molecule have numbers assigned to them. Scientists use these numbers when discussing the structures of sugars. When glucose forms a ring, there are two possible arrangements of the –OH group, which is bound to the carbon at position 1: a-glucose and b-glucose (Figure 2(c), next page). These two different forms of glucose are isomers. An isomer is a molecule that isomer a molecule that has the same has the same chemical formula as another, but a different arrangement of the atoms. composition as another, but a different The different arrangements of the –OH group on glucose can give chemicals different arrangement of atoms properties. For example, humans can easily digest starches composed of a-glucose. However, cellulose, assembled from b-glucose, is completely indigestible for humans. Glucose, fructose, and galactose are isomers of each other. NEL 1.4 Carbohydrates and Lipids   29 7923_Bio_Ch01.indd 29 3/27/12 5:12 PM  H O C HOCH2 OH O CH2OH O H H C OH C C C H H H OH C H C OH H C C H HO C C CH2OH H OH OH OH H glyceraldehyde ribose fructose (a) H O C1 6 CH2OH 6 CH2OH 6 CH2OH 5 5 5 H C2 OH H C OH H H C O H H C O OH 1 1 1 H H H HO C3 H 4C C 4C C 4C C OH H OH H OH H H C4 OH HO 3 C C2 O HO 3 C C2 OH HO 3 C C2 H H C5 OH H OH H OH H OH a-glucose b-glucose H C6 OH H (b) (c) Figure 2 Common monosaccharides are (a) glyceraldehyde, ribose sugar, and fructose sugar. (b) Glucose forms a ring structure due to the interaction of two of its functional groups. (c) There are two possible arrangements of the -OH group on carbon 1 in glucose: a-glucose and b-glucose. Sugars typically have many polar functional groups attached to them. This makes them very hydrophilic and means that small sugars are highly soluble in water. The sweet taste that is associated with carbohydrates requires them to be dissolved in water. Monosaccharides are the sweetest. As the number of monosaccharide units that are linked together increases, the sweetness decreases. Disaccharides disaccharide a carbohydrate molecule that Disaccharides consist of two monosaccharides that are joined together by a dehydra- is made from two monosaccharide units tion synthesis reaction (Section 1.3). For example, the disaccharide maltose forms through the linkage of two a-glucose molecules, with oxygen as a bridge between the 1-carbon of one glucose unit and the 4-carbon of the second glucose unit (Figure 3(a), glycosidic bond a bond between two next page). Bonds of this type, which link monosaccharides into larger carbo- monosaccharides hydrates, are called glycosidic bonds. A glycosidic bond forms between a-glucose and fructose monosaccharide, resulting in the disaccharide sucrose (Figure 3(b), next page). Lactose, the disaccharide milk sugar, forms when galactose and b-glucose bond together (Figure 3(c), next page). The chemical shorthand for representing a glycosidic bond between a 1-carbon and a 4-carbon is 1S 4. Other linkages, such as 1S 2, 1S 3, and 1S 6, are also common in carbohydrate chains. Linkages are designated as a or b, depending on the orientation of the -OH group bonded to the 1-carbon. The linkage in maltose and sucrose is an a-linkage, but the linkage in lactose is a b-linkage. Disaccharide carbohydrate molecules contain the same functional groups that make monosaccharides hydrophilic. Therefore, they are easily dissolved in water. Maple syrup, produced from the sap of maple trees, consists mostly of sucrose mol- ecules dissolved in water (Figure 4). Maple syrup is a sugar source that was first used by Aboriginal people. In the spring, they collected maple sap and boiled it into syrup. Figure 4 Sap from a sugar maple tree Using the knowledge obtained from the Aboriginal people, European settlers learned consists of sucrose molecules dissolved to use maple syrup as a sweetener. Québec is now the world’s largest producer of maple in water. syrup. Other major sources of sucrose (table sugar) are sugar cane and sugar beets. 30 Chapter 1 The Biochemical Basis of Life NEL 7923_Bio_Ch01.indd 30 3/27/12 5:12 PM  6CH2OH 6 CH2OH 6 CH2OH 6 CH2OH 5 5 5 H O H H O H H O H O H 4 H 1  4 H 1 4 H 1 5 2 OH H OH H OH H H HO HO 3 2 OH HO 3 2 OH HO 3 2 O 4 3 1 CH2OH H OH H OH H OH HO H glucose glucose glucose unit fructose unit (b) sucrose 6CH2OH 6CH2OH 6 CH2OH 6 CH2OH H 5 O H H 5 O H HO 5 O H 5 O H 4 H 1 4 H 1  H2O 4 H 1 O 4 H 1 OH H OH H OH H OH H HO 3 2 O 3 2 OH H 3 2 H 3 2 OH H OH H OH H OH H OH maltose galactose unit glucose unit (a) (c) lactose Figure 3 (a) A glycosidic bond between the 1-carbon and 4-carbon atoms of two glucose molecules creates maltose. (b) Sucrose has an a-linkage. (c) Lactose has a b-linkage. Complex Carbohydrates: Polysaccharides Hundreds to thousands of monosaccharides can link together to form a complex carbohydrate. Some complex carbohydrates are important for energy storage complex carbohydrate a molecule that in cells, while others are essential for structural support. Starch and glycogen are is composed of hundreds to thousands examples of storage carbohydrates, and cellulose and chitin are examples of structural of monosaccharides linked together; an complex carbohydrates. essential part of nutrition and a valuable energy source Polysaccharides A polysaccharide molecule is a chain of monosaccharides with many subunits joined polysaccharide molecule a by glycosidic linkages (Figure 5, next page). A polysaccharide is a macromolecule, molecule that contains many linked which is a very large molecule assembled by the covalent linkage of smaller subunit monosaccharides molecules. The dehydration synthesis reactions that assemble polysaccharides are examples of polymerization. Polymerization is the process in which identical or vari- polymerization a process in which able subunits, called monomers, link together in a long chain to form a larger mol- small subunits are linked to form a large ecule. This molecule is called a polymer, hence the term “polymerization.” The linkage molecule of non-identical subunits creates highly diverse and varied biological molecules. monomer a small molecule that can bind Many kinds of polymers are found in cells, not just polysaccharides. For example, chemically to other molecules DNA is another type of polymer. The most common polysaccharides are plant starches, glycogen, and cellulose. polymer a large molecule that is formed They assemble from hundreds or thousands of glucose units. Cellulose is the main when monomers link together chemically component of plant cell walls and the most abundant organic molecule on Earth. in a chain Cellulose molecules are long and straight and have very large numbers of polar OH groups. These two features enable many cellulose molecules to assemble side by side and form hundreds or thousands of hydrogen bonds. These numerous hydrogen bonds are what give cellulose fibres their great strength. Other polysaccharides form from a variety of different sugar monomers. Polysaccharides may be linear unbranched molecules, or they may contain branches in which side chains of sugar units attach to a main chain. Polysaccharides are very polar and therefore very hydrophilic. However, since polysaccharides are such huge molecules, they attract water but cannot dissolve. This is the principle behind absorbent paper towels. Paper towels are made of cel- lulose, a long fibrous polysaccharide. Paper towels attract water, but they do not dissolve in the water. If they did, they would not be useful for cleaning up spills. Table 1 (page 33) is a summary of the different types of carbohydrate molecules. NEL 1.4 Carbohydrates and Lipids   31 7923_Bio_Ch01.indd 31 3/27/12 5:12 PM  CH2OH CH2OH CH2OH H H H H H H H O O O 4 1 4 1 4 1 O O O OH OH OH (a) Amylose grains (stained with a purple dye) in plant root tissue CH2OH CH2OH H H H H O O 4 1 4 1 O O O OH OH CH2OH CH2OH 6 CH2 H H H H H H H O O O 4 1 4 1 4 1 O O O Glycogen particles (stained with OH OH OH a magenta dye) in liver cell (b) CH2OH OH CH2OH OH H H H H H O O O O O O O O H H H H OH CH2OH OH CH2OH glucose Cellulose microfibrils in plant subunit cell wall cellulose molecule cellulose (c) microfibril CH3 C O 6 CH2OH NH CH2OH H H H 5 O O O O 4 1 O 3 2 O O H H H H NH CH2OH NH C O C O CH3 CH3 (d) Chitin in a beetle exoskeleton Figure 5 Examples of polysaccharides and their structure. (a) Amylose is the soluble component of starch. (b) Glycogen is used for energy storage in animals. (c) Cellulose is the main component of plant cell walls. It is the most abundant organic molecule on Earth. (d) Chitin is used by insects and crustaceans to produce hard exoskeleton. It is also a component of fungal cell walls. Chitin is one of the few carbohydrates that contain functional groups with nitrogen atoms. 32 Chapter 1 The Biochemical Basis of Life NEL 7923_Bio_Ch01.indd 32 3/27/12 5:12 PM  Table 1 Structures and Functions of Carbohydrates Type Structure Function Example monosaccharide chain, a-ring, or b-ring energy source, building glucose, ribose, and blocks deoxyribose disaccharide two monomer subunits, energy source sucrose, maltose, with a or b linkage and lactose polysaccharide very long chain or energy storage, starch and cellulose branching chain with structural support, a or b linkages and cell-to-cell communication Mini Investigation Modelling Carbohydrates Mini Investigation skills Skills: Performing, Observing, Analyzing, Evaluating handbook A2.1 In this investigation, you will build and observe three-dimensional A. What is the waste product of the dehydration synthesis models of simple carbohydrates to understand how they are reaction? T/I assembled into larger units. B. What is the overall chemical formula of each of the three Equipment and Materials: chemical modelling kit molecules you created? Determine the C  :  H  :  O ratio for the 1. With a partner, use the chemical modelling kit to construct a monosaccharides. T/I model of a-glucose and a model of fructose. C. How are fructose and glucose similar? How do they differ? 2. Perform a dehydration synthesis reaction to form a sucrose Are they isomers? T/I disaccharide. D. What large polysaccharide is similar to the glucose 3. Perform a hydrolysis reaction to re-form the two chain you created? What other polysaccharide could you monosaccharides. have formed if the glucose molecules had been in their a form? T/I 4. Rearrange the atoms in fructose to change it into glucose. E. Observe the number of OH groups on these molecules. What 5. Convert both glucose molecules to their b forms. Link them can the number of -OH bonds tell you about the molecule using a dehydration reaction. and its relationship with water? How does the -OH group 6. Link your two b-glucose disaccharides with another group’s influence solubility? T/I b-glucose disaccharides. Lipids The term lipid is a general term for a variety of non-polar biological molecules. Lipids lipid a non-polar compound that is made are composed mostly of hydrogen, carbon, and lesser amounts of oxygen. They are mostly of carbon and hydrogen smaller than complex carbohydrates, so they are not considered to be macromol- ecules, and they are not polymers of defined monomeric subunits. Since lipids are generally non-polar, they do not dissolve in water. Their insolubility in water contrib- utes to their ability to form cell membranes. Lipids have other functions as well. Some lipids are stored by cells, to be used as an energy source (Figure 6). Other lipids serve as hormones that regulate cellular activities and as vitamins. Lipids in living organ- isms fall into five main categories: fatty acids, fats, phospholipids, steroids, and waxes. Fatty Acids The structural backbone of most lipids is derived from fatty acids. A fatty acid consists Figure 6 As penguins dive into of a single hydrocarbon chain with a carboxyl functional group (-COOH) at one end extremely cold water, a layer of fat under (Figure 7(a), next page). The carboxyl group gives the fatty acid its acidic properties. their skin acts as thermal insulation. Fatty acids in living organisms contain four or more carbons in their hydrocarbon chain. The most common forms of fatty acids have even-numbered chains of 14 to 22 carbons. fatty acid a molecule that consists of a As their chain length increases, fatty acids become progressively less water soluble. carboxyl group and a hydrocarbon chain NEL 1.4 Carbohydrates and Lipids   33 7923_Bio_Ch01.indd 33 3/27/12 5:12 PM  If the hydrocarbon chain of a fatty acid binds the maximum possible number of hydrogen atoms, and if all the carbons are linked to each other with single bonds, the fatty acid is said to be saturated (Figure 7(b)). If there are double bonds in the fatty acid chain, then it is said to be unsaturated. This means that the carbon chain has the potential to form more bonds with hydrogen (Figure 7(c)). Fatty acids with one double bond are monounsaturated, and those with more than one double bond are polyunsaturated. The presence of a double bond in an unsaturated fatty acid creates a kink in the molecule, which causes it to bend. carboxyl hydrocarbon group chain O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 HO H2C H2C H2C H2C H2C H2C H2C H2C (a) fatty acid (b) stearic acid, CH3(CH2)16COOH (c) oleic acid, CH3(CH2)7CH CH(CH2)7COOH Figure 7 (a) A fatty acid consists of a carboxyl group attached to a long hydrocarbon chain. (b) Stearic acid is a saturated fatty acid. (c) Oleic acid is an unsaturated fatty acid. Fats A fat is a lipid that is made from two types of molecules: fatty acid and a glycerol molecule. In a fat molecule, one to three fatty acid chains are joined to a single glyc- triglyceride a fat; three fatty acid chains erol molecule through dehydration synthesis between -OH functional groups on the linked to a glycerol molecule glycerol and carboxyl functional groups on the fatty acids. Triglycerides are the most well-known fats. They contain three fatty acid chains (Figure 8). A fat molecule can have identical fatty acid chains, or different fatty acid chains, linked to glycerol. glycerol H H H H H H H C C C H H C C C H O O O O O O dehydration H H H synthesis C O C O C O H H H H C H H C H H C H O O O H H H C H H C H H C H C O C O C O O H C H H C H H C H H H H C H H C H H C H O H C H H C H H C H H C H H C H H C H H H H H H O triglyceride H C H H C H H C H H C H H C H H C H H H H 3 fatty acids Figure 8 A triglyceride forming from one glycerol and three fatty acid molecules in a dehydration synthesis reaction 34 Chapter 1 The Biochemical Basis of Life NEL 7923_Bio_Ch01.indd 34 3/27/12 5:13 PM  Different organisms usually have distinctive combinations of fatty acids in their saturated fat a lipid that is composed of triglycerides. For example, fats obtained from animals, such as butter and lard, usu- saturated fatty acids with single bonds in ally contain only saturated fatty acids, so they are called saturated fats. Fats derived their hydrocarbon chain from plants, such as olive oil, usually contain more unsaturated and polyunsaturated unsaturated fat a lipid that is composed fatty acids, so they are called unsaturated fats. Unsaturated fats are generally referred of unsaturated fatty acids with double to as oils. Like individual fatty acids, triglycerides generally become less fluid as the bonds in their hydrocarbon chain length of their fatty acid chain increases. Those with shorter chains remain liquid, as phospholipid a lipid that consists of two oils, at room temperature. The more saturated fats, such as butter, are solids because fatty acids and a phosphate group bound their chains are long and straight and can be packed closely together to form a solid to glycerol structure at room temperature. Fatty acid chains that have kinks are bent and cannot be packed as tightly as saturated fats, Therefore, these molecules stay more fluid and + NH3 are liquid at room temperature. polar Living organisms need flexible cells so they can move around easily. If large unit CH2 amounts of fat in animals were solid, it would be difficult for animals to move about. CH2 Warm-blooded mammals and birds are the exception in having mostly saturated fats, but these fats are liquids because of relatively high body temperature. Many plant seeds O phosphate contain mostly unsaturated fats, which are liquids even at lower temperatures. Cold- – O P O group water fish need their bodies to stay flexible at lower temperatures, so the fats in their bodies are mostly unsaturated fish “oils.” This is one of the benefits of eating fish. glycerol O Triglycerides function widely as stored energy. Gram for gram, they yield more H2C CH CH2 than twice as much energy as carbohydrates. Therefore, fats are an excellent source of energy in a diet. Storing the equivalent amount of energy as carbohydrates rather O O than fats would add more than 45 kg to the average person. A layer of fatty tissue just C O C O under the skin serves as insulation in mammals and birds. Most plant fats are unsaturated fats, which are generally considered healthier than CH2 CH2 saturated animal fats for the human diet. Diets rich in saturated fats can lead to heart H2C H2C disease, whereas diets rich in unsaturated fats can improve your health. The Inuit, CH2 CH2 who live in the Arctic, depend on a diet that is very high in animal proteins from fish, H2C H2C seal, whales, caribou, and waterfowl. Their diet is high in both fat and protein, but CH2 CH2 very low in carbohydrates. The high fat (high energy) content is beneficial for living H2C H2C in such a cold climate. Most of the fats in their diet are made of monounsaturated CH2 CH2 and omega-3 fatty acids. Therefore, the fat they eat is healthier fat than the saturated H2C HC animal fats in a typical North American diet. CH2 HC H2C CH2 Phospholipids CH2 H2C Cells could not exist without the phosphate-containing lipids called phospholipids. H2C CH2 Phospholipids are the primary lipids of cell membranes. In the most common phos- CH2 H2C pholipids, as in triglycerides, glycerol forms the backbone of the molecules. Only two of H2C CH2 its binding sites, however, link to fatty acids. The third site links to a charged phosphate CH2 H2C group, which often binds to another polar or charged unit (Figure 9). Thus, a phospho- H2C CH2 lipid contains two hydrophobic fatty acids at one end, attached to a hydrophilic polar CH3 H3C group, often called the head group (Figure 10(a) and (b), next page). Molecules that contain both hydrophobic and hydrophilic regions are called amphipathic molecules. fatty acid chains The head of an amphipathic molecule is the polar and hydrophilic region. The tail is the Figure 9 A phospholipid has a polar hydrophobic lipid, which is composed of a carbon chain. end and a non-polar end. The non-polar Phospholipids make up the lipid bilayer of cell membranes, an important structural end consists of glycerol bonded to two feature of cells. The hydrophilic end of a phospholipid faces outward toward water, and fatty acids. Phosphattidyl ethanolamine the hydrophobic fatty acid tails face inward toward each other (Figure 10(c), next page). is an example of a phospholipid. NEL 1.4 Carbohydrates and Lipids   35 7923_Bio_Ch01.indd 35 3/27/12 5:13 PM  polar hydrophilic head non-polar hydrophobic tails (b) (a) (c) Figure 10 (a) This structural model of a phospholipid shows the polar and non-polar ends. (b) A phospholipid has a hydrophilic head and two hydrophobic tails. (c) A phospholipid bilayer forms the basic structure of a cell membrane. Steroids steroid a lipid that is composed of four Steroids are a group of lipids with structures that are based on a framework of four carbon rings fused carbon rings. Small differences in the side groups that are attached to the rings distinguish one steroid from another. The most abundant steroids, the sterols, have a OH single polar –OH group at one end of the ring framework and a complex, non-polar CH3 hydrocarbon chain at the other end. Although sterols are almost completely hydro- phobic, the single hydroxyl group gives one end a slightly polar, hydrophilic char- CH3 acter. As a result, sterols also have dual solubility properties and, like phospholipids, testosterone tend to assume positions in cells that satisfy these properties. Cholesterol, a steroid, (an androgen) is an important component of the plasma membrane that surrounds animal cells. O Similar sterols, called phytosterols, occur in plant cell membranes. Cholesterol is a steroid that is essential for animal cell membranes and converts into CH3 a number of compounds, such as vitamin D. Too much dietary cholesterol, however, can be harmful to your body. A high concentration of cholesterol in the bloodstream C O CH3 and a diet rich in saturated fats have been linked to the development of atherosclerosis, a condition in which fat deposits, or plaques, form on the inner lining of blood vessels. CH3 This blocks the flow of blood to tissues, which often leads to a heart attack. Sex hormones, such as testosterone, estrogens, and progesterone, are also steroids progesterone (Figure 11). They control the development of sexual traits and sex cells that are spe- (a progestin) cific to males and females. Anabolic steroids, which are used by some athletes to build O muscle mass, mimic the male sex hormone testosterone. The use of anabolic steroids Figure 11 The sex hormones is banned by all major sporting bodies, yet some athletes still use them to gain an testosterone and progesterone belong advantage over their competitors. Anabolic steroids have many harmful effects on the to the sterol family of lipids. Notice their body, including high blood pressure, depression, suicidal tendencies, changes in the similar four-carbon ring structure. levels of the sex hormones, and, in young people, reduced growth. 36 Chapter 1 The Biochemical Basis of Life NEL 7923_Bio_Ch01.indd 36 3/27/12 5:13 PM  Waxes Waxes are large lipid molecules that are made of long fatty acid chains linked to alco- wax a lipid that is formed when long hols or carbon rings. Waxes are hydrophobic, extremely non-polar, and soft solids fatty acid chains are joined to alcohols or over a wide range of temperatures. These characteristics are what make them ideal for carbon rings flexible waterproof coatings on various plant and animal parts. One type of wax, cutin, is produced by certain plant cells to form a water-resistant coating on the surfaces of stems, leaves, and fruit (Figure 12). Cutin enables plants to conserve water, and it acts as a barrier to infections and diseases. Such functions are vital for life. Without this waxy coating, plants could not survive on land. Birds secrete a waxy material that helps to keep their feathers dry. Bees produce beeswax to make their honeycombs. Table 2 is a summary of the different types of lipid molecules. Table 2 Structure and Function of Lipids Type Structure Function Example fatty acid carboxyl group linked to a cellular functions and stearic acid hydrocarbon chain energy storage fat three fatty acid chains energy storage and butter and olive oil linked to glycerol insulation Figure 12 Cutin, a wax, is produced by phospholipid two fatty acid chains and cell membrane lipid bilayer the fruits, leaves, and stems of plants to one phosphate group linked create a waterproof barrier. to glycerol steroid four carbon rings hormonal signalling, testosterone and cell response to the cholesterol environment, and growth wax long fatty acid chains linked water resistance and wax coating on fruits, to alcohol or carbon rings protection leaves, and stems Mini Investigation Modelling Lipids skills Skills: Performing, Observing, Analyzing, Evaluating handbook A2.1 In this investigation, you will build and observe three-dimensional B. What is the overall chemical formula of the triglyceride? T/I models of simple lipids. C. What is the C  :  H  :  O ratio in the triglyceride you synthesized? Equipment and Materials: chemical modelling kit T/I 1. In pairs, use the chemical modelling kit to construct a D. How does the C   :   H   :   O ratio in triglycerides compare with the model of glycerol and three short fatty acids: a four-carbon overall C  :  H  :  O ratio in carbohydrates? T/I saturated fatty acid, a four-carbon unsaturated fatty acid, E. Which element is less abundant in fats? T/I and a five-carbon saturated fatty acid. F. Compare the polarity of the molecules before and after the 2. Perform three dehydration synthesis reactions to produce formation of the triglyceride. T/I a triglyceride. G. Compare the overall acidity of the molecules before and 3. Perform hydrolysis reactions to re-form the individual after the formation of the triglyceride. T/I components. H. Compare the steroid that your group built with the steroids 4. Research the structure of one steroid of your choosing, that other groups built. Can you identify the steroids that the and build the steroid. other groups built? How are the steroids similar? How are A. Which functional groups are involved in the dehydration they different? T/I C synthesis reactions in Step 2? What are the waste products in this reaction? T/I WEB LINK NEL 1.4 Carbohydrates and Lipids   37 7923_Bio_Ch01.indd 37 3/27/12 5:13 PM  1.4 Review Summary Carbohydrates are simple and complex sugar molecules. They are the most abundant macromolecules found in living things on Earth. Monosaccharides are single sugar molecules that have a 1 : 2 : 1 ratio of C  :  H  :  O. Disaccharides consist of two single sugar subunits that are linked through a dehydration synthesis reaction. Polysaccharides are long chains of sugar monomers. Carbohydrates are polar molecules. They are soluble in water, unless they are very large. Lipids are generally non-polar molecules that do not readily dissolve in water. Fatty acids and triglycerides are primarily energy-storage molecules. Triglycerides consist of three fatty acid chains linked to glycerol. Phospholipids are the main component of all plasma membranes. They are formed from a glycerol molecule, two fatty acids, and an ionic phosphate- containing group. Steroids are small lipids with a four-carbon ring structure. Waxes are long fatty acid chains linked to alcohol or ring structures. They function primarily as waterproofing compounds. Questions 1. (a) Define the term “isomer.” 2. Relate the chemical structure of carbohydrates to (b) Which of the molecules in Figure 13 are their physical properties and uses. K/U isomers? Explain your reasoning. K/U T/I 3. Humans use carbohydrates in many ways. Research how humans use monosaccharides, disaccharides, CH2OH CH2OH 6 and polysaccharides. T/I 5 H C O H HO C O H 4. Compare the polarity of carbohydrates and lipids. 1 4C H C C H C How does their polarity relate to their physical OH H OH H properties? K/U HO 3C C2 OH H C C OH 5. Why are most polysaccharides insoluble in water? K/U H OH H OH 6. (a) Distinguish between a fatty acid and a fat. (i) (iii) (b) What happens to the acidic properties of a fatty acid when a fat is formed? K/U HOCH2 O OH CH2OH O CH2OH 7. Why are steroids important, even though they tend C H H C C H HO C to have a bad reputation? T/I H OH 8. Investigate the use of one performance-enhancing H C C H C C drug in the steroid group. What are the medical OH OH OH H consequences of its use? How do sports federations (ii) (iv) check for the presence of steroids? T/I Figure 13 WEB LINK 38 Chapter 1 The Biochemical Basis of Life NEL 7923_Bio_Ch01.indd 38 3/27/12 5:13 PM