unit 2:chemistry of life

Unit 2:Chemistry of Life

Unit 2:Chemistry of LifePart TwoOrganic MoleculesChemical ReactionsEnzymes

Organic CompoundsSubstances that contain carbon Carbon occurs in almost every chemical compound found in living thingsFour main types of organic compounds in living things: carbohydratesproteinslipids nucleic acids2Combination of carbon and almost any other elementUnique atomic structure allows a carbon atom to link up with as many as four other atoms of another Also links up with other carbon atoms to form long, stable chains, variety of combinations carbon can form with other elements is almost limitlessFYIscientists have already identified more than ten million organic compounds.

2Organic CompoundsOne of the more important properties ofcarbonis its ability to form long chains or sheets.

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Most of the non-metallic elements are capable of forming chains but carbon is unique in being able to form stable chains. (Structurally analogous silanes--mixtures ofsilicon andhydrogen--are spontaneously flammable in air.)Carbon forms many allotropes (property of somechemical elementsto exist in two or more different forms); each has different properties.


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5BiomoleculesComplex compounds in food, such as proteins, fats, and carbohydrates, are broken down into smaller molecules in the body to produce energy. Energy that is not needed immediately is stored in biochemical compounds for later use.Carbohydrates are macro-molecules that function as fuelWhat are carbohydrates?77Hardly a day goes by without an item in a magazine, newspaper, or TV talking about whether carbohydrates are good or bad for us. Sports drinks such as Gatorade are filled with carbs and in the days before a big game or race, athletes often carbo-load by eating bowls of pasta. Yet other dietary supplements and power bars tout that they are low-carb and effective in weight loss by causing the body to resort to using fat for energy. Meanwhile, nutritionists, doctors, and many diet programs exhort people to increase the amount of fiberanother type of carbohydratein their diet. What exactly are they all talking about?If you were going to build a large macromolecule or polymer it needs to be strong. What type of chemical bond do you think would work best for building macromolecules?Covalent

Ionic

Hydrogen8Answer: 18CarbohydratesC, H, and O

Primary fuel for organisms

Cell structure

99Carbohydrates are molecules that contain mostly carbon, hydrogen, and oxygen: they are the primary fuel for running all of the cellular machinery and also form much of the structure of cells in all life forms. Sometimes they contain atoms of other elements, but they must have carbon, hydrogen, and oxygen to be considered a carbohydrate. Further, a carbohydrate generally has approximately the same number of carbon atoms as it does H2O units. For instance, the best-known carbohydrate, glucose, has the composition C6H12O6 (6 carbons and a little math will show us that it also has 6 H2O units; notice that 6 x H2 = H12 and 6 x O = O6). A carbohydrate called maltose has the composition C12H22O11 (Figure 2-20 All carbohydrates have a similar structure and function).

Energy is in the chemical bonds!1010Carbohydrates function well as fuels because their many carbon-hydrogen bonds store a great deal of energy. These C-H bonds are easily broken and organisms can capture the energy released when the bond is broken and put it to use.Simple sugars are the most effective source of energy.Monosaccharides

37 carbon atoms

Glucose and fructose1111Carbohydratesseveral categories, based on their size and their composition. The simplestmonosaccharides or simple sugars. Contain anywhere from three to seven carbon atoms.When broken down, the products usually are not carbohydrates.

Two common monosaccharides are glucose, found in the sap and fruit of many plants, and fructose, found primarily in fruits and vegetables, as well as honey. Fructose is the sweetest of all naturally occurring sugars. The suffix -ose tells us that a substance is a carbohydrate.

1212Unnumbered 2-1 Some Common Monosaccharides. GlucoseMost carbohydrates ultimately converted into glucose

Blood sugar

1313The most important carbohydrate to living organisms is glucose. While it is found naturally in most fruits, most carbohydrates that you eat, including table sugar (called sucrose) and the starchy carbohydrates found in bread and potatoes are ultimately converted into glucose in your digestive system. The glucose then circulates in your blood at a concentration of about 0.1%. Circulating glucose, also called blood sugar, has one of three fates (Figure 2-21 What happens to sugar in your blood?):1) Fuel cellular activity. Once it arrives at a cell it can be used as an energy source. Through a series of chemical reactions the cell breaks the bonds between the atoms of the glucose molecule (a process explained in detail in Chapter 4) and then uses the released energy to fuel cellular activity, including muscle contractions that enable you to move and nerve activities that enable you to think.2) Stored temporarily as glycogen. If there is more glucose circulating in your blood stream than is necessary to meet your bodys current energy needs, the excess glucose can be temporarily stored in various tissues, primarily muscles and your liver. The stored glucose molecules are linked together to form a large web of molecules called glycogen. When you need energy later, the glycogen molecule can be easily broken down to release the glucose molecules back into your blood stream. Glycogen is the primary form of short-term energy storage in animals.3) Converted to fat. And finally, additional glucose circulating in your bloodstream can be converted into fat, another form of long-term energy storage.

1414Glycogen also plays a role in the initial rapid weight loss people experience when dieting. If you reduce your caloric intakeperhaps as part of a low-carbohydrate dietsuch that your body is burning more calories than you are consuming, your body must utilize stored forms of energy. The first, most accessible, molecules that can be broken down for energy in the absence of sufficient sugar in your bloodstream are glycogen molecules in your muscles and liver. Large amounts of water are bound to glycogen, however. In fact, every ounce of stored glycogen has as much as four ounces of water bound to it. As that glycogen is removed from your tissue, so too is the water. This accounts for the initial dramatic weight loss that occurs before your body resorts to utilizing stored fat, at which point the rate of weight loss slows considerably (Figure 2-23 Water weight).When you eat a candy bar you are eating mostly simple sugars. If you eat a candy bar while watching a movie, how will your body utilize those sugars?All of the sugars will be used immediately by your working muscles.The sugars will likely be stored as glycogen.The sugars will likely be stored as fat.Both 2 and 3 are correct.154 is the best answer. Because you are not very physically active while eating the candy bar, the excess energy will most likely be stored as glycogen and fat.15Complex carbohydrates are time-released packets of energy.More than 1 sugar (monosaccharide) unit

Disaccharidessucroselactose

Polysaccharidesstarchcellulose

1616In contrast to the simple sugars, complex carbohydrates contain more than one sugar unit. For example, two simple sugars can be joined together into a disaccharide, such as sucrose (table sugar) and lactose (the sugar found in milk). When many simple sugarssometimes as many as ten thousandare joined together, the resulting molecule is called a polysaccharide (Fig. 2-24). Depending on how the simple sugars are bonded together, they may function as time-release stores of energy or as structural materials that may not be digestible to animals at all. An example of such a structural material is the polysaccharide cellulosethe primary component of plant cell walls. Chemical FuelPreliminary Processing

1717Like simple sugars, many disaccharides and polysaccharides are important sources of fuel. Unlike simple sugars, however, disaccharides and polysaccharides must undergo some preliminary processing before the energy can be released from their bonds. Lets look at what happens when we eat some sucrose, common table sugar. Sucrose is the primary carbohydrate in plant sap. It is a disaccharide composed of two simple sugars, glucose and fructose, linked together. Because humans cant directly utilize sucrose, we first must break the bond linking the glucose and fructose. Only then can the individual monosaccharides be broken down into their component atoms and the energy from the broken bonds be harvested and used. Similarly, lactose is a disaccharide made up of a molecule of glucose and a molecule of galactose bound together. As with sucrose, we must break the bond before we can extract any usable energy from a molecule of lactose.

Figure 2-24 Chains of sugar.Starch> 100s of glucose molecules joined together

Barley, wheat, rye, corn, and rice

Glycogenanimal starch

1818Energy can also be stored in a complex carbohydrate called starch, which consists of a hundred or more glucose molecules joined together in a line. In plants, starch is the primary form of energy storage, found in their roots and other tissues (Fig. 2-24). Commonly cultivated grains such as barley, wheat, and rye are high in starch content, and corn and rice are more than 70% starch. Although it is composed exclusively of glucose molecules linked together, starch does not taste sweet. Because of its shape it does not stimulate the sweetness receptors on the tongue. Because the glycogen that stores energy in your muscles and liver is a complex carbohydrate, it is sometimes referred to as animal starch, (although it is more branched than starch and carries more glucose units linked together).

1919The relative amounts of complex carbohydrates and simple sugars in foods cause them to have very different effects when you eat them. Oatmeal (along with rice and pasta), for example, is rich in complex carbohydrates. Fresh fruits, on the other hand, are rich in simple sugars such as fructose. Consequently, although the fruit will give a quick burst of energy as the sugars are almost immediately available, the fuel will soon be gone from the bloodstream. The simple sugars in the oatmeal will only gradually become available as the complex carbohydrates of the oats are slowly broken down into their simple sugar components(Figure 2-25 Short-term versus long-term energy?).Not all carbohydrates are digestible. Chitin

Cellulose2020Two different complex carbohydratesboth indigestible by humansserve as structural materials for invertebrate animals and plants: chitin (pronounced kite in) and cellulose (Fig. 2-26).

2121Figure 2-26 Carbohydrates can serve as structural materials.

Chitin forms the rigid skeleton of most insects and crustaceans (such as lobsters and crabs). Cellulose forms a huge variety of structures that are visible all around us. We find cellulose in trees and the wooden structures we build from them, in cotton and the clothes we make from it, in leaves, and in grass. In fact, it is the single most prevalent compound on earth.

2222Figure 2-27 Fiber. Because of one small difference in the chemical bond between the simple-sugar units, cellulose has a slightly different three-dimensional structure than starchthe change in shape makes it impossible for humans to digest cellulose as they can starch. Consequently, the cellulose we eat passes right through our digestive system unused.

FiberRoughage

Colon cancer prevention/reduction

Termites ecological role

2323Although it is not digestible, cellulose is still important to human diets. The cellulose in our diet is known as fiber. It is also appropriately called roughage because as the cellulose of celery stalks and lettuce leaves passes through our digestive system, it scrapes the wall of the digestive tract. Its bulk and the scraping stimulate the more rapid passage of food and the nasty byproducts of digestion through our intestines. That is why fiber reduces the risk of colon cancer and other diseases (but it is also why too much fiber can lead to diarrhea.)Unlike humans, termites have some microorganisms living in their gut that are able to break down cellulose. Thats why they can chew on wood and, with the help of the cellulose-digesting boarders in their gut, actually break down the cellulose and extract usable energy from the freed glucose moleculesenergy which is then made available through the food web.Which source of carbohydrates will be digested the slowest?Table sugarHoneyWhole wheat breadApple24Answer: 324Why does a salad dressing made with vinegar and oil separate into two layers shortly after you shake it?Hydrophobic

HydrophilicLipids25Lipids are insoluble in water because, in sharp contrast to water, they consist mostly of hydrocarbons, which are nonpolar. Nonpolar molecules (or parts of molecules) tend to minimize contact with water and are considered hydrophobic. Instead, lipids cluster together when mixed with water, never fully dissolving. Molecules that readily form hydrogen bonds with water, on the other hand, are considered hydrophilic (meaning water loving).

2626One familiar type of lipid is fat, the type most important in long-term energy storage and insulation (Figure 2-28 The many purposes of lipids). (Penguins and walruses can maintain relatively high body temperatures despite living in very cold habitats due to their thick layer of insulating fat.) Lipids also include sterols, which include cholesterol and many of the sex hormones that play regulatory roles in animals, and phospholipids, which form the membranes that enclose cells.We examine each type of lipid next.

2727Section 2-4 Opener A well-insulated harbor seal in Alaska. In making a homemade salad dressing you mix olive oil, vinegar, and water together. You notice when you add the vinegar to the water it mixes immediately. When you add the olive oil it floats on top of the solution. The vinegar is ____________ and the oil is ____________. hydrophobic; hydrophilicacidic; basichydrophilic; hydrophobicbasic; acidic28Answer: 428Fats are tasty molecules too plentiful in our diets. Glycerol: head region

Fatty acid tails

Triglycerides

29All fats have two distinct components: they have a head region, and two or three long tails (Figure 2-29 Triglycerides have glycerol heads and fatty acid tails).The head region is a small molecule called glycerol. It is linked to tail molecules that are called fatty acids. A fatty acid is simply a long hydrocarbon, that is, a chain of carbon molecules, often a dozen or more, linked together with one or two hydrogen atoms attached to each carbon.

The fats in most foods we eat are triglycerides, which are fats having three fatty acids linked to the glycerol molecule. For this reason, the terms fats and triglycerides are often used interchangeably. Triglycerides that are solid at room temperature are called fats, while those that are liquid at room temperature are called oils.Fat molecules contain much more stored energy than carbohydrate molecules.

30Fat molecules contain much more stored energy than carbohydrate molecules. That is, the chemical breakdown of fat molecules releases significantly more energy. A single gram of carbohydrates stores about four calories of energy, while the exact same amount of fat stores about 9 caloriesnot unlike the difference between a five dollar bill and a ten dollar bill. Because fats store such a large amount of energy, animals have evolved a strong taste preference for fats over other energy sources (Figure 2-30 Animals (including humans!) prefer the taste of fats). Organisms evolving in an environment of uncertain food supply will build the largest surplus by consuming molecules that hold the most amount of energy in the smallest mass. This feature helped humans to survive millions of years ago, but today puts us in danger from the health risks of obesity now that fats are all too readily available.Saturated and Unsaturated Fats# of bonds in the hydrocarbon chain in a fatty acidHealth considerations

31An important distinction is made between saturated and unsaturated fats (Figure 2-31 Degrees of saturation).These terms refer to the hydrocarbon chain in the fatty acids. If each carbon atom in the hydrocarbon chain in a fatty acid is bonded to two hydrogen atoms, the fat molecule carries the maximum number of hydrogen atoms and is said to be saturated. Most animal fats, including those found in meat, cheese, and eggs, are saturated. They are not essential to your health and, because they accumulate in your bloodstream and can narrow the vessel walls, they can cause heart disease and strokes.A fat is unsaturated if any of its carbon atoms are bound to only a single hydrogen. Most plant fats are unsaturated. Unsaturated fats may be mono-unsaturated (if the hydrocarbon chain has only one carbon in an unsaturated state) or polyunsaturated (if more than one carbon is unsaturated). Unsaturated fats are still high in calories, but because they can lower cholesterol, they are generally preferable to saturated fats. Foods high in unsaturated fats include avocados, peanuts, and olive oil. Relative to other animal fats, fish tend to have less saturated fat.

The shapes of unsaturated fat molecules and saturated fat molecules are different. When saturated, the hydrocarbon tails of the fatty acids all line up very straight and the fat molecules can be packed together tightly. The tight packing causes the fats to be solid at room temperature, like butter. When unsaturated, the fatty acids have kinks in the hydrocarbon tail and cannot be packed together as tightly. Consequently, unsaturated fats, such as canola oil and vegetable oil, do not solidify so easily and are liquid at room temperature.What are trans fats?Many snack foods contain partially hydrogenated vegetable oils.

Why might it be desirable to add hydrogen atoms to a vegetable oil?32The ingredient list for many snack foods lists partially hydrogenated vegetable oils. The hydrogenation of an oil means that a liquid, unsaturated fat has had additional hydrogen atoms added to it, so that it becomes more saturated. This can be useful in creating a food with a more desirable texture because increasing a fats degree of saturation changes its consistency and makes it more solid at room temperatures.

3333Figure 2-32 (part 1) Hydrogenation improves a food's taste, texture, and shelf-life (but at a cost).

By attaining just the right degree of saturation, it is possible to create foods near the border of solid and liquid, like chocolate, that melt in your mouth (Fig. 2-32[b1]). Unfortunately, hydrogenation makes the food less healthful because saturated fats are less reactiveyour body is less likely to break them downand so they are more likely to accumulate in your blood vessels, increasing risk of heart disease.

3434Figure 2-32 (part 2) Hydrogenation improves a food's taste, texture, and shelf-life (but at a cost).

Hydrogenation of unsaturated fats is problematic from a health perspective, however, because it creates trans fats, referring to the unusual orientation of the hydrogen atoms added, which differs from other dietary fats, which have their hydrogens in an orientation called cis. Trans fats cause your body to produce more cholesterol, further raising the risk of heart disease, and they also reduce your bodys production of a type of cholesterol that protects against heart disease.

Which answer below is solid at room temperature? Saturated fat (like animal fat) Unsaturated fat (like canola oil)Trans fat (like margarine)Both 1 and 3 are correct.35Answer: 435Cholesterol and phospholipids are used to build sex hormones and membranes.Not all lipids are fats

The sterols

36Not all lipids are fats, nor do they necessarily function in energy storage. A second group of lipids, called the sterols plays an important role in regulating growth and development (Fig. 2-34).

3737Figure 2-33 Not all lipids are for energy storage. Cholesterol, estrogen, and testosterone are all lipids.

This group includes some very familiar lipids: cholesterol and the steroid hormones such as testosterone and estrogen. These molecules are all modifications on one basic structure formed of four interlinked rings of carbon atoms.

Steroid HormonesEstrogen

Testosteronesynthetic variants of testosterone

38The steroid hormones estrogen and testosterone are built by slight chemical modifications to cholesterol. These are among the primary molecules that direct and regulate sexual development, maturation, and sperm and egg production. In both males and females, estrogen influences memory and mood, among other traits. Testosterone has numerous effects, one of which is to stimulate muscle growth. As a consequence, athletes often take synthetic variants of testosterone to increase their muscularity. But the usage of these supplements is often accompanied by dangerous side effects, though, including extreme aggressiveness (roid rage), high cholesterol, and, following long-term use, cancer. As a consequence, nearly all athletic organizations have banned their use.

Figure 2-34 Dangerous bulk.Phospholipids and WaxesPhospholipids are the major component of the cell membrane.

Waxes are strongly hydrophobic.39Phospholipids and waxes are also lipids. Phospholipids are the major component of the membrane that surrounds the contents of a cell and controls the flow of chemicals into and out of the cell. They have a structure similar to fats, but with two differences: they contain a phosphorous atom (hence phospholipids) and they have two fatty acid chains rather than three. We will explore the significant role of phospholipids in cell membranes in the next chapter.

Waxes resemble fats but have only one long-chain fatty acid, linked to the glycerol head of the molecule. Because the fatty acid chain is highly nonpolar, waxes are strongly hydrophobic; that is, these molecules do not mix with water but repel it. Their water resistance accounts for their use as a natural coating on the surface of many plants and their use in the outer coverings of many insects. In both cases the waxes prevent the plants and animals from losing water essential to their life processes. Many birds, too, have a waxy coating on their wings, keeping them from becoming water-logged when they get wet.

4040Figure 2-35 Lipid versatility. Phospholipids have important roles in many organisms. Proteins are versatile macromolecules that serve as building blocks.

41You cant look at a living organism and not see proteins (Figure 2-36 Proteins everywhere!). Inside and out, proteins are the chief building blocks of all life. They make up skin and feathers and horns. They make up bones and muscles. In your bloodstream, proteins fight invading microorganisms and stop you from bleeding to death from a shaving cut. Proteins control the levels of sugar and other chemicals in your bloodstream and carry oxygen from one place in your body to another. And in just about every cell in every living organism, proteins called enzymes initiate and assist all chemical reactions that occur.Amino AcidsTwenty different amino acids

Strung together to make proteins42Although proteins perform several very different types of functions, they are all built in the same way and from the same raw materials in all organisms. In the English language, every sentence is made of words and every word is formed from the 26 letters of the alphabet. Twenty-six letters and we can write anything from sonnets to ghost stories to biology textbooks. Proteins, too, are constructed from a sort of alphabet. Instead of 26 letters, there are 20 molecules, known as amino acids. Unique combinations of these 20 amino acids are strung together, like beads on a string, and the resulting protein has a unique structure and chemical behavior.

43Lets look more closely at the structure of the amino acids in the protein alphabet. They all have the same basic two-part structure: one part is the same in all 20 amino acids, and the other part is unique, differing in each of the 20 amino acids.Proteins contain the same familiar atoms as carbohydrates and lipidscarbon, hydrogen, and oxygenbut differ in an important way: they also contain nitrogen. At the center of every amino acid is a carbon atom, with four covalent bonds (Figure 2-37 Amino acid structure).One bond attaches the carbon to something called a carboxyl group, which is a carbon bonded to two oxygen atoms. The second bond attaches the central carbon to a single hydrogen atom. The third bond attaches the central carbon to an amino group, which is a nitrogen atom bonded to three hydrogen atoms. These components are the foundation that identifies a molecule as an amino acid and, as multiple amino acids are joined together, form the backbone of the protein.

The fourth bond attaches the central carbon to a functional group or side chain. This side chain is the unique part of each of the 20 amino acids. In the simplest amino acid, glycine, for example, the side chain is simply a hydrogen atom. In other amino acids, the side chain is a single CH3 group or three or four such groups. Most of the side chains include both hydrogen and carbon, and a few include nitrogen or sulfur atoms. The side chain determines an amino acids chemical properties, such as whether the amino acid molecule is polar or nonpolar.Proteins are an essential dietary component.Growth

Repair

Replacement44The atoms present in the plant and animal proteins we eatespecially nitrogenare essential to the constant growth, repair, and replacement that take place in our bodies. As we eat protein and break it down into its parts through digestion, our bodies are collecting the amino acids needed for various building projects. Proteins also store energy in their bonds and, like carbohydrates and lipids, they can also be used to fuel living processes. The amount of protein we need depends on the extent of the building projects underway at any given time. Most individuals need 40 to 80 grams of protein per day. Bodybuilders, however, may need 150 grams a day or more to achieve the extensive muscle growth stimulated by their training; similarly, the protein needs of pregnant or nursing women are very high as well. Food labels indicate an items protein content.

Why is this insufficient for you to determine whether you are protein deficient, even if your protein intake exceeds your recommended daily amount?45Contrary to the labels we see on food packaging, all proteins are not created equal.Every different protein has a different composition of amino acids. And while our bodies can manufacture certain amino acids as needed, many others must come from our diet. Those that must come from our dietabout half of the 20 amino acidsare called essential amino acids. For this reason, we shouldnt just speak of needing x grams of protein per day. We need to consume all of the essential amino acids every day.Complete ProteinsHave all essential amino acids

Incomplete proteins

Complementary proteins46Many foods, called complete proteins, have all of the essential amino acids. Animals products such as milk, eggs, fish, chicken, and beef tend to provide complete proteins. Most vegetables, fruits, and grains, on the other hand, more often contain incomplete proteins, which do not have all essential amino acids. If you consume only one type of incomplete protein in your diet, you may be deficient in one or more of the essential amino acids. Two incomplete proteins (called complementary proteins) eaten together, however, can provide all essential amino acids. Traditional dishes in many cultures often include such pairings. Examples are corn and beans in Mexico, rice and lentils in India, and rice and black-eyed peas in the southern United States.Which answer below will provide all of the essential amino acids in a meal?HamburgerCorn and a legume (complementary)AppleBoth 1 and 2 are correct.47Answer: 447Protein functions are influenced by their three-dimensional shape.Peptide bonds48Proteins are formed by linking individual amino acids together with a peptide bond, in which the amino group of one amino acid is bonded to the carboxyl group of another (Figure 2-39 Protein structure). Two amino acids joined together is a dipeptide, and several amino acids joined together is a polypeptide. Primary StructureThe sequence of amino acids

49The sequence of amino acids in the polypeptide chain is called the primary structure of the protein, and can be compared to the sequence of letters that spells a specific word.

Figure 2-39 part 1 Protein structure.Secondary StructureHydrogen bonding between amino acidsThe two most common patterns:twist in a corkscrew-like shapezig-zag folding

50Amino acids dont remain in a simple straight line like beads on a string, though. The chain begins to fold as side chains come together and hydrogen bonds form between various atoms within the chain. The two most common patterns of hydrogen bonding between amino acids cause the chain to either twist in a corkscrew-like shape or into a zig-zag folding. This hydrogen bonding between amino acids gives a protein its secondary structure.

Figure 2-39 part 2 Protein structure.

Tertiary StructureFolding and bending of the secondary structure

Due to bonds such as hydrogen bonds or covalent sulfur-sulfur bonds.

51The protein eventually folds and bends upon itself and additional bonds continue to form between atoms within the side chains of amino acids that are near each other. Eventually, the protein folds into a unique and complex three-dimensional shape called its tertiary structure. The exact form comes about as the secondary structure folds and bends, bringing together amino acids that then form bonds such as hydrogen bonds or covalent sulfur-sulfur bonds.


Quaternary StructureWhen two or more polypeptide chains are held together by bonds between the amino acids on the different chains.

Hemoglobin

52Some protein molecules have a quaternary structure in which two or more polypeptide chains are held together by bonds between the amino acids on the different chains. Hemoglobin, the protein molecule that carries oxygen from the lungs to the cells where it is needed, is made from four polypeptide chains, two alpha chains and two beta chains.


Egg whites contain much protein.

Why does beating them change their texture, making them stiff?53For proteins to function properly, they must retain their three-dimensional shape. When their shapes are deformed, they usually lose their ability to function. We can see proteins deformed when we fry an egg. The heat breaks the hydrogen bonds giving the protein its shape. The proteins in the clear egg white unfold, losing their secondary and tertiary structure. Disruption of protein folding is called denaturation.Egg whites contain much protein.Why does beating them change their texture, making them stiff?

54Disruption of protein folding is called denaturation (Figure 2-40 Denaturation).

Almost any extreme environment will denature a protein. Take a raw egg, for instance, and crack it into a dish containing baking soda or rubbing alcohol. Both chemicals are sufficiently extreme to turn the protein white like fried egg whites.Why is wet hair easier to style than dry hair?55Hair is a protein whose shape we all have modified at one time or another. Styling hairwhether curling or straightening itinvolves altering some of the hydrogen bonds that occur between the amino acids that make up your hair, changing the hair proteins tertiary structure. When your hair gets wet, the water is able to disrupt some of these hydrogen bonds, causing some amino acids to form hydrogen bonds with the water molecules instead. This enables you to change your hairs shapemaking it straighter or, if you manipulate it around curlers, making it curlierif you style it while wet. It can then hold this shape when it dries as the hydrogen bonds to the water are replaced by other hydrogen bonds between amino acids of the hair as the water evaporates. Once your hair gets wet again, however, unless it is combed, brushed or wrapped in a different style it will return to its natural shape.Why do some people have curly hair and others have straight hair?

56Whether your hair is straight or curly or somewhere in between also depends on the proteins amino acid sequences and the three-dimensional shape they confer (Figure 2-41 Curly or straight?).This amino acid sequence is something youre born with. The chains become more or less coiled, depending on the extent of covalent and hydrogen bonding between different parts of the coil. Many hair salons make use of the ability to alter covalent bonds to change hair texture semi-permanently. They are able to do this in three simple steps. First, the bonds are broken chemically. Second, the hair is wrapped around curlers holding the polypeptide chains in a different position. And third, chemicals are put on the hair to create new covalent bonds between parts of the polypeptide chains. The hair thus becomes locked in the new position. (New hair will continue to grow with its genetically determined texture, of course, requiring the procedure to be repeated regularly.)A proteins function is most dependent onits shape.its size.its color.Both 2 and 3 are correct.57Answer: 157Enzymes are proteins that initiate and speed up chemical reactions.58Protein shape is particularly critical in enzymes, molecules that help initiate and accelerate the chemical reactions in our bodies. Enzymes emerge in their original form when the reaction is complete and thus can be used again and again.

59Think of an enzyme as a big piece of popcorn. Its tertiary or quaternary structure gives it a complex shape with lots of nooks and crannies. Within one of those nooks is a small area called the active site (Figure 2-42 part 1 Lock and key). Based on the chemical properties of the atoms lining this pocket, the active site provides a place for the reactants, called substrate molecules, to nestle briefly.

60Enzymes are very choosy: they bind only with their appropriate substrate molecules, much like a lock that can be opened with one key (Figure 2-42 part 2 Lock and key). The exposed atoms in the active site have electrical charges that attract rather than repel the substrate molecules, and only the substrate molecules can fit into the active site groove. Once the substrate is bound to the active site, a reaction can take placeand usually does very quickly.

An enzyme can help to bring about the reaction in a variety of ways. These include:1) By stressing, bending, or stretching critical chemical bonds, increasing their likelihood of breaking.2) By directly participating in the reaction, perhaps temporarily sharing one or more electrons with the substrate molecule, thereby giving it chemical features that increase its ability to make or break other bonds.3) By creating a microhabitat that is conducive to the reaction. For instance, the active site might be a water-free, nonpolar environment, or it might have a slightly higher or lower pH than the surrounding fluid. Both of these slight alterations might increase the likelihood that a particular reaction occurs.4) By simply orienting or holding substrate molecules in place so that they can be modified.Misspelled ProteinsIncorrect amino acid sequence

Active site disruptions

Phenylketonuria61Sometimes a protein word is misspelled in that the sequence of amino acids is incorrect. If an enzyme is altered even slightly, the active site may change and the enzyme no longer functions. Slightly modified, nonfunctioning enzymes are responsible for a large number of diseases and physiological problems, including the inability to break down the amino acid phenylalanine (phenylketonuria) among many others.Why do some adults get sick when they drink milk?

62One protein misspelling is responsible for the condition called lactose intolerance. Normally, during digestion the lactose in milk is broken down into its component parts, glucose and galactose. The simple sugars are then used for energy. But some people are unable to break the bond linking the two simple sugars because they lack a functioning version of the enzyme lactase that assists in this process. Consequently, the lactose passes through their stomach and small intestine undigested. Then, when it reaches the large intestine, bacteria living inside us consume it. The problem is, as they break down the lactose, they produce some carbon dioxide and other hydrogen gases. These gases are trapped in the intestine and lead to severe discomfort. These unpleasant symptoms can be avoided by not consuming milk, cheese, yogurt, ice cream or any other dairy products, but they can also be avoided by taking a pill containing the enzyme lactase. It doesnt matter how the enzyme gets there, as long as it is in your digestive system the lactose in the milk can be broken down.

Figure 2-42 part 3 Lock and key.Nucleic acids are macromolecules that store information.

63We have examined three of lifes macromolecules: carbohydrates, lipids, and proteins. We turn our attention now to the fourth: nucleic acids, macromolecules that store information and are made up of individual units called nucleotides. All nucleotides have three components: a molecule of sugar, a phosphate group (containing a phosphorous atom bound to four oxygen atoms), and a nitrogen-containing molecule (Figure 2-43 The molecules that carry genetic information).Two Types of Nucleic AcidsDeoxyribonucleic acid (DNA)

Ribonucleic acid (RNA)

Both play central roles in directing the production of proteins.

64There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both play central roles in directing the production of proteins in living organisms, and by doing so play a central role in determining all of the inherited characteristics of an individual. In both types of nucleic acids, the molecule has a consistent backbone: a sugar molecule attached to a phosphate group attached to another sugar, then another phosphate, and so on. Attached to each sugar is one of the nitrogen-containing molecules, called DNA bases due to their chemical structure. A ten-unit nucleic acid therefore would have ten bases, one attached to each sugar within the sugar-phosphate backbone. But the base attached to each sugar is not always the same. It can be one of several different bases. For this reason, a nucleic acid is often described by the sequence of bases attached to the sugar-phosphate backbone.

Figure 2-43 The molecules that carry genetic information.Information StorageThe information in a molecule of DNA is determined by its sequence of bases.

Adenine, guanine, cytosine, and thymine

CGATTACCCGAT65Nucleic acids are able to store information by varying which base is attached at each position within the molecule. At each position in a molecule of DNA, for example, the base can be any one of four possible bases: adenine (A), thymine (T), guanine (G), or cytosine (C). Just as the meaning of a sentence is determined by which letters are strung together, the information in a molecule of DNA is determined by its sequence of bases. One molecule may have the sequence adenine, adenine, adenine, guanine, cytosine, thymine guanineabbreviated as AAAGCTG. Another molecule may have the sequence CGATTACCCGAT. Because the information differs in each case, so too does the protein for which the sequence codes.DNA holds the genetic information to build an organism.

66A molecule of DNA has two strands, each a sugar-phosphate-sugar-phosphate backbone with a base sticking out from each sugar molecule. The two strands wrap around each other, each turning in a spiral. Although each strand has its own sugar-phosphate-sugar-phosphate backbone and sequence of bases, the two strands are connected by the bases protruding from them. You can imagine a molecule of DNA as a ladder. The two sugar-phosphate-sugar-phosphate backbones are like the long vertical elements of the ladder that give it height. A base sticking out represents a rung on the ladder. Or, more accurately, half a rung. The bases protruding from each strand meet in the center and bind to each other (via hydrogen bonds), holding the ladder together. DNA differs from a ladder slightly, in that it has a gradual twist. The two spiraling strands together are said to form a double helix (Figure 2-44 A gradually twisting ladder).Base-PairingA & T

G & C

What is the complimentary strand to this strand: CCCCTTAGGAACC?67The two intertwining spirals fit together because only two combinations of bases pair up together. The base A always pairs with T and C always pairs with G. Consequently, if the base sequence of one of the spirals is CCCCTTAGGAACC, the base sequence of the other must be GGGGAATCCTTGG. That is why researchers working on the Human Genome Project describe only one sequence of nucleotides when presenting a DNA sequence. With that sequence, we can infer the identity of the bases in the complementary sequence and thus we know the exact structure of the nucleic acid.The sequence of base pairs containing the information about how to produce a particular protein may be anywhere from a hundred bases to several thousand. In a human, all of the DNA in a cell, containing all of the instructions for every protein that a human must produce, contains about three billion base pairs. This DNA is generally in the nucleus of a cell.RNA is a universal translator, reading DNA and directing protein production.

68The process of building a protein from a DNA sequence is not a direct one. Rather, it incorporates a middle man, RNA, that is also a nucleic acid (Fig. 2-45 part 1 The middleman between DNA and protein). Segments of the DNA are read off, directing the production of short strips of RNA that contain the information from the DNA about the amino acid sequence in a protein. The RNA moves to another part of the cell and then directs the piecing together of amino acids into a three-dimensional protein. We explore this in greater detail in Chapter 5.

6969Figure 2-45 part 2 The middleman between DNA and protein. The structure of RNA.

RNA differs from DNA in three important ways. The sugar molecule of the sugar-phosphate backbone

Single-stranded

Uracil (U) replaces thymine (T)

70RNA differs from DNA in three important ways. First, the sugar molecule of the sugar-phosphate backbone differs slightly, containing an extra atom of oxygen. Second, RNA is single stranded. The sugar-phosphate-sugar-phosphate backbone is still there, as is the base that protrudes from each sugar. The bases, however, do not bind with anything else. And third, while RNA has the bases A, G, and C, it replaces the thymine with a similar base called uracil (U).Given the DNA sequence below, what is the sequence of the RNA?

CGATTCACTGCCGATTCACTGCGCTAAGTGACGGCUAAGUGACGGCAGTGAATCG71Answer: 371

unit 2:chemistry of life

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carbon carbon

carbon atoms

stable chains

long chains

different properties

different forms

variety of combinations

organic compoundsone