3.1 Life’s molecular diversity is based on the properties of carbon

3.1 Life’s molecular diversity is based on the properties of carbon
Diverse molecules found in cells are composed of carbon bonded to other elements Carbon-based molecules are called organic compounds By sharing electrons, carbon can bond to four other atoms By doing so, it can branch in up to four directions The ability to bond in four directions is called tetravalence. This is one facet of carbon’s versatility that makes large, complex molecules possible. One of the great advantages of life based on carbon is its ability to form up to four bonds, permitting the assembly of diverse components and branching configurations. Challenge your students to find another element that might also permit this sort of adaptability. (Like carbon, silicon has four electrons in its outer shell.) Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. 2. Students might need to be reminded about the levels of biological organization. The relationship between atoms, monomers, and polymers can be confusing as each is discussed. Consider noting these relationships somewhere in the classroom (such as on the board) where students can quickly glance for reassurance. Teaching Tips 1. One of the great advantages of carbon is its ability to form up to four bonds, permitting the assembly of diverse components and branching configurations. Challenge your students to find another element that might also permit this sort of adaptability. (Like carbon, silicon has four electrons in its outer shell.) 2. Toothpicks and gumdrops (or any other pliable small candy) permit the quick construction of chemical models. Different candy colors can represent certain atoms. The model of the methane molecule in Figure 3.1 can thus easily be demonstrated (and consumed!). Copyright © 2009 Pearson Education, Inc.

Methane (CH4) is one of the simplest organic compounds Four covalent bonds link four hydrogen atoms to the carbon atom Each of the four lines in the formula for methane represents a pair of shared electrons Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. 2. Students might need to be reminded about the levels of biological organization. The relationship between atoms, monomers, and polymers can be confusing as each is discussed. Consider noting these relationships somewhere in the classroom (such as on the board) where students can quickly glance for reassurance. Teaching Tips 1. One of the great advantages of carbon is its ability to form up to four bonds, permitting the assembly of diverse components and branching configurations. Challenge your students to find another element that might also permit this sort of adaptability. (Like carbon, silicon has four electrons in its outer shell.) 2. Toothpicks and gumdrops (or any other pliable small candy) permit the quick construction of chemical models. Different candy colors can represent certain atoms. The model of the methane molecule in Figure 3.1 can thus easily be demonstrated (and consumed!). Copyright © 2009 Pearson Education, Inc.

The four single bonds of carbon point to the corners
Structural formula Ball-and-stick model Space-filling model Methane Figure 3.1A Three representations of methane (CH4). Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. 2. Students might need to be reminded about the levels of biological organization. The relationship between atoms, monomers, and polymers can be confusing as each is discussed. Consider noting these relationships somewhere in the classroom (such as on the board) where students can quickly glance for reassurance. Teaching Tips 1. One of the great advantages of carbon is its ability to form up to four bonds, permitting the assembly of diverse components and branching configurations. Challenge your students to find another element that might also permit this sort of adaptability. (Like carbon, silicon has four electrons in its outer shell.) 2. Toothpicks and gumdrops (or any other pliable small candy) permit the quick construction of chemical models. Different candy colors can represent certain atoms. The model of the methane molecule in Figure 3.1 can thus easily be demonstrated (and consumed!). The four single bonds of carbon point to the corners of a tetrahedron.

Methane and other compounds composed of only carbon and hydrogen are called hydrocarbons Carbon, with attached hydrogens, can bond together in chains of various lengths Hydrocarbons are the major components of petroleum. Hydrocarbons consist of the partially decomposed remains of organisms that lived millions of years ago. Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. 2. Students might need to be reminded about the levels of biological organization. The relationship between atoms, monomers, and polymers can be confusing as each is discussed. Consider noting these relationships somewhere in the classroom (such as on the board) where students can quickly glance for reassurance. Teaching Tips 1. One of the great advantages of carbon is its ability to form up to four bonds, permitting the assembly of diverse components and branching configurations. Challenge your students to find another element that might also permit this sort of adaptability. (Like carbon, silicon has four electrons in its outer shell.) 2. Toothpicks and gumdrops (or any other pliable small candy) permit the quick construction of chemical models. Different candy colors can represent certain atoms. The model of the methane molecule in Figure 3.1 can thus easily be demonstrated (and consumed!). Copyright © 2009 Pearson Education, Inc.

A chain of carbon atoms is called a carbon skeleton Carbon skeletons can be branched or unbranched Therefore, different compounds with the same molecular formula can be produced These structures are called isomers You may want to give an example of an isomer. Students can relate to the isomers glucose and galactose, because both are energy sources for organisms. Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. 2. Students might need to be reminded about the levels of biological organization. The relationship between atoms, monomers, and polymers can be confusing as each is discussed. Consider noting these relationships somewhere in the classroom (such as on the board) where students can quickly glance for reassurance. Teaching Tips 1. One of the great advantages of carbon is its ability to form up to four bonds, permitting the assembly of diverse components and branching configurations. Challenge your students to find another element that might also permit this sort of adaptability. (Like carbon, silicon has four electrons in its outer shell.) 2. Toothpicks and gumdrops (or any other pliable small candy) permit the quick construction of chemical models. Different candy colors can represent certain atoms. The model of the methane molecule in Figure 3.1 can thus easily be demonstrated (and consumed!). Copyright © 2009 Pearson Education, Inc.

3.2 Characteristic chemical groups help determine the properties of organic compounds
An organic compound has unique properties that depend upon The size and shape of the molecule and The groups of atoms (functional groups) attached to it A functional group affects a biological molecule’s function in a characteristic way Functional groups may participate in chemical reactions or may contribute to function indirectly by their effects on molecular shape. A drill with interchangeable drill bits is a nice analogy to carbon skeletons with different functional groups. The analogy relates the role of different functions with different structures. Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. Teaching Tips 1. A drill with interchangeable drill bits is a nice analogy to carbon skeletons with different functional groups. The analogy relates the role of different functions to different structures. Copyright © 2009 Pearson Education, Inc.

Compounds containing functional groups are hydrophilic (water-loving) This means that they are soluble in water, which is a necessary prerequisite for their roles in water-based life Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. Teaching Tips 1. A drill with interchangeable drill bits is a nice analogy to carbon skeletons with different functional groups. The analogy relates the role of different functions to different structures. Copyright © 2009 Pearson Education, Inc.

The functional groups are Hydroxyl group—consists of a hydrogen bonded to an oxygen Carbonyl group—a carbon linked by a double bond to an oxygen atom Carboxyl group—consists of a carbon double-bonded to both an oxygen and a hydroxyl group Amino group—composed of a nitrogen bonded to two hydrogen atoms and the carbon skeleton Phosphate group—consists of a phosphorus atom bonded to four oxygen atoms You may want to add the methyl group as a functional group because of its importance in methylating certain compounds. For example, a methyl group on DNA may affect expression of genes. Another example is the arrangement of methyl groups in male and female sex hormones to affect their shape and function. Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. Teaching Tips 1. A drill with interchangeable drill bits is a nice analogy to carbon skeletons with different functional groups. The analogy relates the role of different functions to different structures. Copyright © 2009 Pearson Education, Inc.

Table 3.2 Functional Groups of Organic Compounds.

3.3 Cells make a huge number of large molecules from a small set of small molecules
There are four classes of biological molecules Carbohydrates Proteins Lipids Nucleic acids Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. Teaching Tips 1. Train cars linking together to form a train is a nice analogy to linking monomers to form polymers. Consider adding that as the train cars are joined, a puff of steam appears—thus the reference to water production and a dehydration reaction when linking molecular monomers. Copyright © 2009 Pearson Education, Inc.

The four classes of biological molecules contain very large molecules They are often called macromolecules because of their large size They are also called polymers because they are made from identical building blocks strung together The building blocks are called monomers Macromolecules are large and complex. A protein may consist of thousands of atoms that form a molecular colossus with a mass well over 100,000 daltons. Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. Teaching Tips 1. Train cars linking together to form a train is a nice analogy to linking monomers to form polymers. Consider adding that as the train cars are joined, a puff of steam appears—thus the reference to water production and a dehydration reaction when linking molecular monomers. Copyright © 2009 Pearson Education, Inc.

A cell makes a large number of polymers from a small group of monomers Proteins are made from only 20 different amino acids, and DNA is built from just four kinds of nucleotides The monomers used to make polymers are universal As an example of the universality of monomers, the amino acids in your student’s proteins are the same ones found in a bacterium’s or plant’s proteins. Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. Teaching Tips 1. Train cars linking together to form a train is a nice analogy to linking monomers to form polymers. Consider adding that as the train cars are joined, a puff of steam appears—thus the reference to water production and a dehydration reaction when linking molecular monomers. Copyright © 2009 Pearson Education, Inc.

Monomers are linked together to form polymers through dehydration reactions, which remove water Polymers are broken apart by hydrolysis, the addition of water All biological reactions of this sort are mediated by enzymes, which speed up chemical reactions in cells The bulk of the organic material we ingest is in the form of polymers that are much too large to enter our cells. Within our digestive tract, various enzymes attack the polymers, speeding up hydrolysis. Student Misconceptions and Concerns 1. General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. Teaching Tips 1. Train cars linking together to form a train is a nice analogy to linking monomers to form polymers. Consider adding that as the train cars are joined, a puff of steam appears—thus the reference to water production and a dehydration reaction when linking molecular monomers. Animation: Polymers Copyright © 2009 Pearson Education, Inc.

Short polymer Unlinked monomer
Figure 3.3A Dehydration reactions build a polymer chain.

Short polymer Unlinked monomer Dehydration reaction Longer polymer
Figure 3.3A Dehydration reactions build a polymer chain. Longer polymer

Figure 3.3B Hydrolysis breaks a polymer chain.

Hydrolysis Figure 3.3B Hydrolysis breaks a polymer chain.

3.4 Monosaccharides are the simplest carbohydrates
Carbohydrates range from small sugar molecules (monomers) to large polysaccharides Sugar monomers are monosaccharides, such as glucose and fructose These can be hooked together to form the polysaccharides Monosaccharides have molecular formulae that are multiples of CH2O. Student Misconceptions and Concerns 1. The abstract nature of chemistry can be discouraging to many students. Consider starting out this section of the lecture by examining the chemical groups on a food nutrition label. Candy bars with peanuts are particularly useful, as they contain significant amounts of all three sources of calories (carbohydrates, proteins, and lipids). 2. Consider reinforcing the three main sources of calories with food items that clearly represent each group. Bring clear examples to class as visual references. For example, a can of Coke or a bag of sugar for carbohydrates, a tub of margarine for lipids, and some beef jerky for protein (although some fat and carbohydrates might also be included). Teaching Tips 1. If your lectures will eventually include details of glycolysis and aerobic respiration, this is a good point to introduce the basic concepts of glucose as fuel. Just introducing this conceptual formula might help: eating glucose + breathing in oxygen → water + usable energy (used to build ATP) + heat + exhaling CO2. Copyright © 2009 Pearson Education, Inc.

3.4 Monosaccharides are the simplest carbohydrates
The carbon skeletons of monosaccharides vary in length Glucose and fructose are six carbons long Others have three to seven carbon atoms Monosaccharides are the main fuels for cellular work Monosaccharides are also used as raw materials to manufacture other organic molecules Monosaccharides, particularly glucose, are major nutrients for cells. Glucose is the starting compound for an important metabolic pathway called cellular respiration. If your lectures will eventually include details of cellular respiration (glycolysis or aerobic respiration), this is a good point to introduce the basic concepts of glucose as fuel. Student Misconceptions and Concerns 1. The abstract nature of chemistry can be discouraging to many students. Consider starting out this section of the lecture by examining the chemical groups on a food nutrition label. Candy bars with peanuts are particularly useful, as they contain significant amounts of all three sources of calories (carbohydrates, proteins, and lipids). 2. Consider reinforcing the three main sources of calories with food items that clearly represent each group. Bring clear examples to class as visual references. For example, a can of Coke or a bag of sugar for carbohydrates, a tub of margarine for lipids, and some beef jerky for protein (although some fat and carbohydrates might also be included). Teaching Tips 1. If your lectures will eventually include details of glycolysis and aerobic respiration, this is a good point to introduce the basic concepts of glucose as fuel. Just introducing this conceptual formula might help: eating glucose + breathing in oxygen → water + usable energy (used to build ATP) + heat + exhaling CO2. Copyright © 2009 Pearson Education, Inc.

Glucose (an aldose) Fructose (a ketose)
Figure 3.4B Structures of glucose and fructose. Glucose (an aldose) Fructose (a ketose)

3.5 Cells link two single sugars to form disaccharides
Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction An example is a glucose monomer bonding to a fructose monomer to form sucrose, a common disaccharide Sucrose is the sugar (disaccharide) we keep around the kitchen to sweeten coffee or use for dozens of other things. Student Misconceptions and Concerns 1. The abstract nature of chemistry can be discouraging to many students. Consider starting out this section of the lecture by examining the chemical groups on a food nutrition label. Candy bars with peanuts are particularly useful, as they contain significant amounts of all three sources of calories (carbohydrates, proteins, and lipids). 2. Consider reinforcing the three main sources of calories with food items that clearly represent each group. Bring clear examples to class as visual references. For example, a can of Coke or a bag of sugar for carbohydrates, a tub of margarine for lipids, and some beef jerky for protein (although some fat and carbohydrates might also be included). Teaching Tips 1. Learning the definitions of word roots is invaluable when learning science. Learning the meaning of the prefix word roots “mono” (one), “di” (two), and “poly” (many) helps to distinguish the structures of various carbohydrates. Animation: Disaccharides Copyright © 2009 Pearson Education, Inc.

Glucose Glucose Figure 3.5 Disaccharide formation by a dehydration reaction.

Glucose Glucose Maltose
Figure 3.5 Disaccharide formation by a dehydration reaction. Maltose

3.7 Polysaccharides are long chains of sugar units
Starch is a storage polysaccharide composed of glucose monomers and found in plants Glycogen is a storage polysaccharide composed of glucose, which is hydrolyzed by animals when glucose is needed Cellulose is a polymer of glucose that forms plant cell walls Chitin is a polysaccharide used by insects and crustaceans to build an exoskeleton Most mammals, including humans, do not have enzymes necessary to digest cellulose. Thus the energy in the glucose monomers is not available. Cows have solved this problem by harboring prokaryotes (bacteria) in their rumen that hydrolyze the cellulose of grass and hay to glucose monomers. The glucose can be used for energy as well as building blocks for other nutrients that nourish the cow. Likewise, termites cannot digest cellulose in wood, but the bacteria in their guts can, and so provide a meal for themselves as well as the termites The text notes that cellulose is the most abundant organic molecule on Earth. Ask your students why this is true. Student Misconceptions and Concerns 1. Consider reinforcing the three main sources of calories with food items that clearly represent each group. Bring clear examples to class as visual references. For example, a can of Coke or a bag of sugar for carbohydrates, a tub of margarine for lipids, and some beef jerky for protein (although some fat and carbohydrates might also be included). Teaching Tips 1. A simple exercise demonstrates the enzymatic breakdown of starches into sugars. If students place an unsalted cracker in their mouths, holding it in their mouths while it mixes well with saliva, they might soon notice that a sweeter taste begins to emerge. The salivary enzyme amylase begins the digestion of starches into disaccharides, which may be degraded further by other enzymes. These disaccharides are the source of the sweet taste. 2. The text notes that cellulose is the most abundant organic molecule on Earth. Ask your students why this is true. 3. The cellophane wrap often used to package foods is a biodegradable material derived from cellulose. Consider challenging students to create a list of other cellulose-derived products (such as paper.) 4. An adult human may store about a half kilogram of glycogen in the liver and muscles of the body, depending upon recent dietary habits. A person who begins dieting might soon notice an immediate weight loss of 2–4 pounds (1–2 kilograms) over several days, reflecting reductions in stored glycogen, water, and intestinal contents (among other factors). Copyright © 2009 Pearson Education, Inc.

3.7 Polysaccharides are long chains of sugar units
Polysaccharides are hydrophilic (water-loving) Cotton fibers, such as those in bath towels, are water absorbent Student Misconceptions and Concerns 1. Consider reinforcing the three main sources of calories with food items that clearly represent each group. Bring clear examples to class as visual references. For example, a can of Coke or a bag of sugar for carbohydrates, a tub of margarine for lipids, and some beef jerky for protein (although some fat and carbohydrates might also be included). Teaching Tips 1. A simple exercise demonstrates the enzymatic breakdown of starches into sugars. If students place an unsalted cracker in their mouths, holding it in their mouths while it mixes well with saliva, they might soon notice that a sweeter taste begins to emerge. The salivary enzyme amylase begins the digestion of starches into disaccharides, which may be degraded further by other enzymes. These disaccharides are the source of the sweet taste. 2. The text notes that cellulose is the most abundant organic molecule on Earth. Ask your students why this is true. 3. The cellophane wrap often used to package foods is a biodegradable material derived from cellulose. Consider challenging students to create a list of other cellulose-derived products (such as paper.) 4. An adult human may store about a half kilogram of glycogen in the liver and muscles of the body, depending upon recent dietary habits. A person who begins dieting might soon notice an immediate weight loss of 2–4 pounds (1–2 kilograms) over several days, reflecting reductions in stored glycogen, water, and intestinal contents (among other factors). Animation: Polysaccharides Copyright © 2009 Pearson Education, Inc.

3.8 Fats are lipids that are mostly energy-storage molecules
Lipids are water insoluble (hydrophobic, or water fearing) compounds that are important in energy storage They contain twice as much energy as a polysaccharide Fats are lipids made from glycerol and fatty acids Lipids are generally not big enough to be macromolecules. They are grouped together because they mix poorly, if at all, with water. Student Misconceptions and Concerns 1. Students may struggle with the concept that a pound of fat contains more than twice the calories of a pound of sugar. It might seem that a pound of food would potentially add on a pound of weight. Other students may have never understood the concept of calories in the diet, simply following general guidelines of avoiding fatty foods. Furthermore, fiber and water have no caloric value but add to the weight of food. Consider class discussions that explore student misconceptions about calories, body weight, and healthy diets. 2. Students might struggle to extrapolate the properties of lipids to their roles in an organism. Ducks float because their feathers repel water instead of attracting it. Hair on our heads remains flexible because of oils produced in our scalp. Examples such as these help connect the abstract properties of lipids to concrete examples in our world. Teaching Tips 1. The text in Module 3.8 notes the common observation that vinegar and oil do not mix in this type of salad dressing. A simple demonstration can help make this point. In front of the class, mix together colored water and a yellow oil (corn or canola oil work well). Shake up the mixture and then watch as the two separate. (You may have a mixture already made ahead of time that remains separated; however, the dye may bleed between the oil and the water.) Placing the mixture on an overhead projector or other well-illuminated imaging device makes for a dramatic display of hydrophobic activity! 2. The text notes that a gram of fat stores more than twice the energy of a gram of polysaccharide, such as starch. You might elaborate with a simple calculation to demonstrate how a person’s body weight would vary if the energy stored in body fat were stored in carbohydrates instead. If a 100-kg man carried 25% body fat, he would have 25 kg of fat in his body. Fat stores about 2.25 times more energy per gram than carbohydrate. What would be the weight of the man if he stored the energy in the fat in the form of carbohydrate? (2.25  25  kg of carbohydrate  75 kg  kg, an increase of 31.25%) 3. Margarine in stores commonly comes in liquid squeeze containers, in tubs, and in sticks. These forms reflect increasing amounts of hydrogenation, gradually increasing the stiffness from a liquid, to a firmer spread, to a firm stick of margarine. As noted in the text, recent studies have suggested that unsaturated oils become increasingly unhealthy as they are hydrogenated. Public attention to hydrogenation and the health risks of the resulting trans fats are causing changes in the use of products containing trans fats. Copyright © 2009 Pearson Education, Inc.

Figure 3.8A Water beading on the only coating of feathers.

Fatty acids link to glycerol by a dehydration reaction A fat contains one glycerol linked to three fatty acids Fats are often called triglycerides because of their structure Student Misconceptions and Concerns 1. Students may struggle with the concept that a pound of fat contains more than twice the calories of a pound of sugar. It might seem that a pound of food would potentially add on a pound of weight. Other students may have never understood the concept of calories in the diet, simply following general guidelines of avoiding fatty foods. Furthermore, fiber and water have no caloric value but add to the weight of food. Consider class discussions that explore student misconceptions about calories, body weight, and healthy diets. 2. Students might struggle to extrapolate the properties of lipids to their roles in an organism. Ducks float because their feathers repel water instead of attracting it. Hair on our heads remains flexible because of oils produced in our scalp. Examples such as these help connect the abstract properties of lipids to concrete examples in our world. Teaching Tips 1. The text in Module 3.8 notes the common observation that vinegar and oil do not mix in this type of salad dressing. A simple demonstration can help make this point. In front of the class, mix together colored water and a yellow oil (corn or canola oil work well). Shake up the mixture and then watch as the two separate. (You may have a mixture already made ahead of time that remains separated; however, the dye may bleed between the oil and the water.) Placing the mixture on an overhead projector or other well-illuminated imaging device makes for a dramatic display of hydrophobic activity! 2. The text notes that a gram of fat stores more than twice the energy of a gram of polysaccharide, such as starch. You might elaborate with a simple calculation to demonstrate how a person’s body weight would vary if the energy stored in body fat were stored in carbohydrates instead. If a 100-kg man carried 25% body fat, he would have 25 kg of fat in his body. Fat stores about 2.25 times more energy per gram than carbohydrate. What would be the weight of the man if he stored the energy in the fat in the form of carbohydrate? (2.25  25  kg of carbohydrate  75 kg  kg, an increase of 31.25%) 3. Margarine in stores commonly comes in liquid squeeze containers, in tubs, and in sticks. These forms reflect increasing amounts of hydrogenation, gradually increasing the stiffness from a liquid, to a firmer spread, to a firm stick of margarine. As noted in the text, recent studies have suggested that unsaturated oils become increasingly unhealthy as they are hydrogenated. Public attention to hydrogenation and the health risks of the resulting trans fats are causing changes in the use of products containing trans fats. Animation: Fats Copyright © 2009 Pearson Education, Inc.

Glycerol Fatty acid Figure 3.8B A dehydration reaction linking a fatty acid to glycerol.

Figure 3.8C A fat molecule made from glycerol and three fatty acids.

Some fatty acids contain double bonds This causes kinks or bends in the carbon chain because the maximum number of hydrogen atoms cannot bond to the carbons at the double bond These compounds are called unsaturated fats because they have fewer than the maximum number of hydrogens Fats with the maximum number of hydrogens are called saturated fats Most animal fat is saturated fat. Saturated fats, such as butter and lard, will pack tightly together and will be solid at room temperature. Plant and fish fats are usually unsaturated fats. They are usually liquid at room temperature. Olive oil and cod liver oil are examples. Peanut butter, margarine, and many other products are hydrogenated to prevent lipids from separating out in liquid (oil) form. Student Misconceptions and Concerns 1. Students may struggle with the concept that a pound of fat contains more than twice the calories of a pound of sugar. It might seem that a pound of food would potentially add on a pound of weight. Other students may have never understood the concept of calories in the diet, simply following general guidelines of avoiding fatty foods. Furthermore, fiber and water have no caloric value but add to the weight of food. Consider class discussions that explore student misconceptions about calories, body weight, and healthy diets. 2. Students might struggle to extrapolate the properties of lipids to their roles in an organism. Ducks float because their feathers repel water instead of attracting it. Hair on our heads remains flexible because of oils produced in our scalp. Examples such as these help connect the abstract properties of lipids to concrete examples in our world. Teaching Tips 1. The text in Module 3.8 notes the common observation that vinegar and oil do not mix in this type of salad dressing. A simple demonstration can help make this point. In front of the class, mix together colored water and a yellow oil (corn or canola oil work well). Shake up the mixture and then watch as the two separate. (You may have a mixture already made ahead of time that remains separated; however, the dye may bleed between the oil and the water.) Placing the mixture on an overhead projector or other well-illuminated imaging device makes for a dramatic display of hydrophobic activity! 2. The text notes that a gram of fat stores more than twice the energy of a gram of polysaccharide, such as starch. You might elaborate with a simple calculation to demonstrate how a person’s body weight would vary if the energy stored in body fat were stored in carbohydrates instead. If a 100-kg man carried 25% body fat, he would have 25 kg of fat in his body. Fat stores about 2.25 times more energy per gram than carbohydrate. What would be the weight of the man if he stored the energy in the fat in the form of carbohydrate? (2.25  25  kg of carbohydrate  75 kg  kg, an increase of 31.25%) 3. Margarine in stores commonly comes in liquid squeeze containers, in tubs, and in sticks. These forms reflect increasing amounts of hydrogenation, gradually increasing the stiffness from a liquid, to a firmer spread, to a firm stick of margarine. As noted in the text, recent studies have suggested that unsaturated oils become increasingly unhealthy as they are hydrogenated. Public attention to hydrogenation and the health risks of the resulting trans fats are causing changes in the use of products containing trans fats. Copyright © 2009 Pearson Education, Inc.

3.9 Phospholipids and steroids are important lipids with a variety of functions
Phospholipids are structurally similar to fats and are an important component of all cells For example, they are a major part of cell membranes, in which they cluster into a bilayer of phospholipids The hydrophilic heads are in contact with the water of the environment and the internal part of the cell The hydrophobic tails band in the center of the bilayer The phospholipid bilayer provides the cell with a structure that separates the outside from the inside of the cell. The integrity of the membrane is necessary for life functions. Because of the nature of the phospholipid, many molecules cannot move across the membrane without help. Student Misconceptions and Concerns 1. Students might struggle to extrapolate the properties of lipids to their roles in an organism. Ducks float because their feathers repel water instead of attracting it. Hair on our heads remains flexible because of oils produced in our scalp. Examples such as these help connect the abstract properties of lipids to concrete examples in our world. Teaching Tips 1. Before explaining the properties of a polar molecule such as a phospholipid, have students predict the consequences of adding phospholipids to water. See if the class can generate the two most common configurations: (1) a lipid bilayer encircling water (water surrounding the bilayer and contained internally) and (2) a micelle (polar heads in contact with water and hydrophobic tails clustered centrally). 2. The consequences of steroid abuse will likely be of great interest to your students. However, the reasons for the damaging consequences might not be immediately clear. As time permits, consider noting the diverse homeostatic mechanisms that normally regulate the traits affected by steroid abuse. Copyright © 2009 Pearson Education, Inc.

Water Hydrophilic heads Hydrophobic tails Water
Figure 3.9A Section of a phospholipid membrane. Water

3.11 Proteins are essential to the structures and functions of life
A protein is a polymer built from various combinations of 20 amino acid monomers Proteins have unique structures that are directly related to their functions Enzymes, proteins that serve as metabolic catalysts, regulate the chemical reactions within cells Proteins account for more than 50% of the dry mass of cells. Teaching Tips 1. Many analogies help students appreciate the diversity of proteins that can be made from just 20 amino acids. The authors note that our language uses combinations of 26 letters to form words. Proteins are much longer “words,” creating even more diversity. Another analogy is to trains. This builds upon the earlier analogy when polymers were introduced. Imagine making different trains about 100 cars long, using any combination of 20 types of railroad cars. Mathematically, the number of possible trains is 20100, a number beyond imagination. Copyright © 2009 Pearson Education, Inc.

3.11 Proteins are essential to the structures and functions of life
Structural proteins provide associations between body parts and contractile proteins are found within muscle Defensive proteins include antibodies of the immune system, and signal proteins are best exemplified by the hormones Receptor proteins serve as antenna for outside signals, and transport proteins carry oxygen Teaching Tips 1. Many analogies help students appreciate the diversity of proteins that can be made from just 20 amino acids. The authors note that our language uses combinations of 26 letters to form words. Proteins are much longer “words,” creating even more diversity. Another analogy is to trains. This builds upon the earlier analogy when polymers were introduced. Imagine making different trains about 100 cars long, using any combination of 20 types of railroad cars. Mathematically, the number of possible trains is 20100, a number beyond imagination. Copyright © 2009 Pearson Education, Inc.

3.12 Proteins are made from amino acids linked by peptide bonds
Amino acids, the building blocks of proteins, have an amino group and a carboxyl group Both of these are covalently bonded to a central carbon atom Also bonded to the central carbon is a hydrogen atom and some other chemical group symbolized by R Teaching Tips 1. Many analogies help students appreciate the diversity of proteins that can be made from just 20 amino acids. The authors note that our language uses combinations of 26 letters to form words. Proteins are much longer “words,” creating even more diversity. Another analogy is to trains. This builds upon the earlier analogy when polymers were introduced. Imagine making different trains about 100 cars long, using any combination of 20 types of railroad cars. Mathematically, the number of possible trains is 20100, a number beyond imagination. 2. The authors note that the difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! Copyright © 2009 Pearson Education, Inc.

Amino group Carboxyl group
Figure 3.12A General structure of an amino acid.

Amino acids are classified as hydrophobic or hydrophilic Some amino acids have a nonpolar R group and are hydrophobic Others have a polar R group and are hydrophilic, which means they easily dissolve in aqueous solutions Teaching Tips 1. Many analogies help students appreciate the diversity of proteins that can be made from just 20 amino acids. The authors note that our language uses combinations of 26 letters to form words. Proteins are much longer “words,” creating even more diversity. Another analogy is to trains. This builds upon the earlier analogy when polymers were introduced. Imagine making different trains about 100 cars long, using any combination of 20 types of railroad cars. Mathematically, the number of possible trains is 20100, a number beyond imagination. 2. The authors note that the difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! Copyright © 2009 Pearson Education, Inc.

Leucine (Leu) Serine (Ser) Aspartic acid (Asp) Hydrophobic Hydrophilic
Figure 3.12B Examples of amino acids with hydrophobic and hydrophilic R groups. Leucine (Leu) Serine (Ser) Aspartic acid (Asp) Hydrophobic Hydrophilic

Amino acid monomers are linked together to form polymeric proteins This is accomplished by an enzyme-mediated dehydration reaction This links the carboxyl group of one amino acid to the amino group of the next amino acid The covalent linkage resulting is called a peptide bond Teaching Tips 1. Many analogies help students appreciate the diversity of proteins that can be made from just 20 amino acids. The authors note that our language uses combinations of 26 letters to form words. Proteins are much longer “words,” creating even more diversity. Another analogy is to trains. This builds upon the earlier analogy when polymers were introduced. Imagine making different trains about 100 cars long, using any combination of 20 types of railroad cars. Mathematically, the number of possible trains is 20100, a number beyond imagination. 2. The authors note that the difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! Copyright © 2009 Pearson Education, Inc.

Carboxyl group Amino group Amino acid Amino acid
Figure 3.12C Peptide bond formation. As more and more amino acids are added, a chain of amino acids called a polypeptide results. The combination of amino acids is determined by expression of genes on DNA. Although there seems to be an unlimited number of combinations of 20 amino acids, the combinations are limited in an individual because of inheritance.

Peptide bond Carboxyl group Amino group Dehydration reaction
Amino acid Amino acid Dipeptide Figure 3.12C Peptide bond formation. As more and more amino acids are added, a chain of amino acids called a polypeptide results. The combination of amino acids is determined by expression of genes on DNA. Although there seems to be an unlimited number of combinations of 20 amino acids, the combinations are limited in an individual because of inheritance.

3.13 A protein’s specific shape determines its function
A polypeptide chain contains hundreds or thousands of amino acids linked by peptide bonds The amino acid sequence causes the polypeptide to assume a particular shape The shape of a protein determines its specific function Because of the molecular structure of specific proteins on brain cells, endorphins bind to them. This gives us a feeling of euphoria and pain relief. Morphine, heroin, and other opiate drugs are able to mimic endorphins and bind to the endorphin receptors in the brain. Because of the euphoria that results, we become addicted. Student Misconceptions and Concerns 1. The functional significance of protein shape is an abstract molecular example of form and function relationships, which might be new to some students. The binding of an enzyme to its substrate is a type of molecular handshake, which permits specific interactions. To help students think about form and function relationships, share some concrete analogies in their lives—perhaps flathead and Phillips screwdrivers that match the proper type of screws or the fit of a hand into a glove. Teaching Tips 1. Most cooking results in changes in the texture and color of food. The brown color of a cooked steak is the product of the denaturation of proteins. Fixatives such as formalin also denature proteins and cause color changes. Students who have dissected vertebrates will realize that the brown color of the muscles makes it look as if the animal has been cooked. Copyright © 2009 Pearson Education, Inc.

Groove Figure 3.13B Space-filling model of lysozyme.

3.13 A protein’s specific shape determines its function
If for some reason a protein’s shape is altered, it can no longer function Denaturation will cause polypeptide chains to unravel and lose their shape and, thus, their function Proteins can be denatured by changes in salt concentration and pH Excessive heat can also denature a protein. A good example is frying or boiling an egg. The proteins in the egg “white” become solid, white, and opaque upon denaturation. Student Misconceptions and Concerns 1. The functional significance of protein shape is an abstract molecular example of form and function relationships, which might be new to some students. The binding of an enzyme to its substrate is a type of molecular handshake, which permits specific interactions. To help students think about form and function relationships, share some concrete analogies in their lives—perhaps flathead and Phillips screwdrivers that match the proper type of screws or the fit of a hand into a glove. Teaching Tips 1. Most cooking results in changes in the texture and color of food. The brown color of a cooked steak is the product of the denaturation of proteins. Fixatives such as formalin also denature proteins and cause color changes. Students who have dissected vertebrates will realize that the brown color of the muscles makes it look as if the animal has been cooked. Copyright © 2009 Pearson Education, Inc.

3.14 A protein’s shape depends on four levels of structure
A protein can have four levels of structure Primary structure Secondary structure Tertiary structure Quaternary structure For the BLAST Animation Alpha Helix, go to Animation and Video Files. Teaching Tips 1. Consider this assignment to review the organic molecules in our diets. Have students, working individually or in small groups, analyze a food label listing the components of a McDonalds’ Big Mac or other fast-food sandwich. Note the most abundant organic molecule class (perhaps by weight) found in each component. Copyright © 2009 Pearson Education, Inc.

3.14 A protein’s shape depends on four levels of structure
The primary structure of a protein is its unique amino acid sequence The correct amino acid sequence is determined by the cell’s genetic information The slightest change in this sequence affects the protein’s ability to function Sickle cell disease is manifested by an inability of hemoglobin in red blood cells to carry oxygen, the primary function of hemoglobin. This blood disorder is the result of change in a single amino acid. Teaching Tips 1. Consider this assignment to review the organic molecules in our diets. Have students, working individually or in small groups, analyze a food label listing the components of a McDonalds’ Big Mac or other fast-food sandwich. Note the most abundant organic molecule class (perhaps by weight) found in each component. Copyright © 2009 Pearson Education, Inc.

Four Levels of Protein Structure
Primary structure Amino acids Hydrogen bond Secondary structure Alpha helix Pleated sheet Tertiary structure Figure 3.14A Primary structure. Figure 3.14B Secondary structure. Figure 3.14C Tertiary structure. Figure 3.14D Quaternary structure. Polypeptide (single subunit of transthyretin) Transthyretin, with four identical polypeptide subunits Quaternary structure

Amino acids Primary structure
Figure 3.14A Primary structure.

3.15 TALKING ABOUT SCIENCE: Linus Pauling contributed to our understanding of the chemistry of life
After winning a Nobel Prize in Chemistry, Pauling spent considerable time studying biological molecules He discovered an oxygen attachment to hemoglobin as well as the cause of sickle-cell disease Pauling also discovered the alpha helix and pleated sheet of proteins Pauling was also an advocate for halting nuclear weapons testing and won the Nobel Peace Prize for his work. He was very close to reporting the structure of DNA when Watson and Crick scooped him and correctly described its structure. Teaching Tips 1. An examination of the fabrics and weave of a sweater might help students understand the levels of protein structure. Although not a perfect analogy, levels of organization can be better appreciated. Teasing apart a single thread reveals a simpler organization of smaller fibers woven together. In turn, threads are interlaced into a connected fabric, which may be further twisted and organized into a pattern or structural component of a sleeve. Challenge students to identify the limits of this analogy and identify aspects of protein structure not included (such as the primary structure of a protein, its sequence of amino acids). 2. Additional details of Linus Pauling’s career can be found on the website of the Linus Pauling Institute at Oregon State University, Copyright © 2009 Pearson Education, Inc.

Dehydration Hydrolysis Short polymer Monomer Longer polymer

Sucrose

Enzyme A Enzyme B Rate of reaction 20 40 60 80 100 Temperature (°C)

You should now be able to
Discuss the importance of carbon to life’s molecular diversity Describe the chemical groups that are important to life Explain how a cell can make a variety of large molecules from a small set of molecules Define monosaccharides, disaccharides, and polysaccharides and explain their functions Define lipids, phospholipids, and steroids and explain their functions Copyright © 2009 Pearson Education, Inc.

You should now be able to
Describe the chemical structure of proteins and their importance to cells Describe the chemical structure of nucleic acids and how they relate to inheritance Copyright © 2009 Pearson Education, Inc.

3.1 Life’s molecular diversity is based on the properties of carbon

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3.1 Life’s molecular diversity is based on the properties of carbon

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