* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Macromolecules
Survey
Document related concepts
Protein purification wikipedia , lookup
Fluorescent glucose biosensor wikipedia , lookup
Protein–protein interaction wikipedia , lookup
Western blot wikipedia , lookup
Two-hybrid screening wikipedia , lookup
Expanded genetic code wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Nutrition transition wikipedia , lookup
Chemical biology wikipedia , lookup
List of nutrition guides wikipedia , lookup
Protein adsorption wikipedia , lookup
Biomolecular engineering wikipedia , lookup
Transcript
Macromolecules and Nutrition Macro means large Macromolecules are large complex molecules essential for life Carbohydrates Lipids Proteins Nucleic Acids Human Nutrition Human Nutrition, study of how food affects the health and survival of the human body. Human beings require food to grow, reproduce, and maintain good health. Without food, our bodies could not stay warm, build or repair tissue, or maintain a heartbeat. Eating the right foods can help us avoid certain diseases or recover faster when illness occurs. Human Nutrition These and other important functions are fueled by chemical substances in our food called nutrients. Nutrients are classified as carbohydrates, proteins, fats, vitamins, minerals, and water. When we eat a meal, nutrients are released from food through digestion. Human Nutrition: Digestion Digestion begins in the mouth by the action of chewing and the chemical activity of saliva, a watery fluid that contains enzymes, certain proteins that help break down food. Human Nutrition: Digestion Further digestion occurs as food travels through the stomach and the small intestine, where digestive enzymes and acids liquefy food and muscle contractions push it along the digestive tract. Holt, Modern Biology Human Nutrition: Digestion Nutrients are absorbed from the inside of the small intestine into the bloodstream and carried to the sites in the body where they are needed. At these sites, several chemical reactions occur that ensure the growth and function of body tissues. The parts of foods that are not absorbed continue to move down the intestinal tract and are eliminated from the body as feces. Human Nutrition: Digestion Once digested, carbohydrates, proteins, and fats provide the body with the energy it needs to maintain its many functions. Scientists measure this energy in kilocalories, the amount of energy needed to raise 1 kilogram of water 1 degree Celsius. In nutrition discussions, scientists use the term calorie instead of kilocalorie as the standard unit of measure in nutrition. Nutrition: Nutrients Nutrients are classified as essential or nonessential. Nonessential nutrients are manufactured in the body and do not need to be obtained from food. Examples include cholesterol, a fatlike substance present in all animal cells. Nutrition: Nutrients Essential nutrients must be obtained from food sources, because the body either does not produce them or produces them in amounts too small to maintain growth and health. Essential nutrients include water, carbohydrates, proteins, fats, vitamins, and minerals. Nutrition: Nutrients An individual needs varying amounts of each essential nutrient, depending upon such factors as gender and age. Specific health conditions, such as pregnancy, breast-feeding, illness, or drug use, make unusual demands on the body and increase its need for nutrients. Dietary guidelines, which take many of these factors into account, provide general guidance in meeting daily nutritional needs. Nutrition: Nutrients If the importance of a nutrient is judged by how long we can do without it, water ranks as the most important. A person can survive only eight to ten days without water, whereas it takes weeks or even months to die from a lack of food. Nutrition: Water Water circulates through our blood and lymphatic system, transporting nutrients to cells and removing wastes through urine and sweat. Water also maintains the natural balance between dissolved salts and water inside and outside of cells. Our joints and soft tissues depend on the cushioning that water provides for them. Nutrition: Water While water has no caloric value and therefore is not an energy source, without it in our diets we could not digest or absorb the foods we eat or eliminate the body’s digestive waste. The human body is 65 percent water, and it takes an average of eight to ten cups to replenish the water our bodies lose each day. Nutrition: Water How much water a person needs depends largely on the volume of urine and sweat lost daily, and water needs are increased if a person suffers from diarrhea or vomiting or undergoes heavy physical exercise. Water is replenished by drinking liquids, preferably those without caffeine or alcohol, both of which increase the output of urine and thus dehydrate the body. Nutrition: Water Many foods are also a good source of water—fruits and vegetables, for instance, are 80 to 95 percent water; meats are made up of 50 percent water; and grains, such as oats and rice, can have as much as 35 percent water. Nutrition: Carbohydrates Carbohydrates are the human body’s key source of energy, providing 4 calories of energy per gram. When carbohydrates are broken down by the body, the sugar glucose is produced; glucose is critical to help maintain tissue protein, metabolize fat, and fuel the central nervous system and body cells. Nutrition: Carbohydrates Glucose is absorbed into the bloodstream through the intestinal wall. Some of this glucose goes straight to work in our brain cells and red blood cells, while the rest makes its way to the liver and muscles, where it is stored as glycogen (animal starch), and to fat cells, where it is stored as fat. Glycogen is the body’s auxiliary energy source, tapped and converted back into glucose when we need more energy. Nutrition: Carbohydrates Although stored fat can also serve as a backup source of energy, it is never converted into glucose. Fructose and galactose, other sugar products resulting from the breakdown of carbohydrates, go straight to the liver, where they are converted into glucose. Nutrition: Carbohydrates Starches and sugars are the major carbohydrates. Common starch foods include whole-grain breads and cereals, pasta, corn, beans, peas, and potatoes. Naturally occurring sugars are found in fruits and many vegetables; milk products; and honey, maple sugar, and sugar cane. Nutrition: Carbohydrates Foods that contain starches and naturally occurring sugars are referred to as complex carbohydrates, because their molecular complexity requires our bodies to break them down into a simpler form to obtain the much-needed fuel, glucose. Our bodies digest and absorb complex carbohydrates at a rate that helps maintain the healthful levels of glucose already in the blood. Nutrition: Carbohydrates In contrast, simple sugars, refined from naturally occurring sugars and added to processed foods, require little digestion and are quickly absorbed by the body, triggering an unhealthy chain of events. The body’s rapid absorption of simple sugars elevates the levels of glucose in the blood, which triggers the release of the hormone insulin. Nutrition: Carbohydrates Insulin reins in the body’s rising glucose levels, but at a price: Glucose levels may fall so low within one to two hours after eating foods high in simple sugars, such as candy, that the body responds by releasing chemicals known as antiinsulin hormones. This surge in chemicals, the aftermath of eating a candy bar, can leave a person feeling irritable and nervous. Nutrition: Carbohydrates Many processed foods not only contain high levels of added simple sugars, they also tend to be high in fat and lacking in the vitamins and minerals found naturally in complex carbohydrates. Nutritionists often refer to such processed foods as junk foods and say that they provide only empty calories, meaning they are loaded with calories from sugars and fats but lack the essential nutrients our bodies need. Nutrition: Carbohydrates In addition to starches and sugars, complex carbohydrates contain indigestible dietary fibers. Although such fibers provide no energy or building materials, they play a vital role in our health. Found only in plants, dietary fiber is classified as soluble or insoluble. Nutrition: Carbohydrates Soluble fiber, found in such foods as oats, barley, beans, peas, apples, strawberries, and citrus fruits, mixes with food in the stomach and prevents or reduces the absorption by the small intestine of potentially dangerous substances from food. Soluble fiber also binds dietary cholesterol and carries it out of the body, thus preventing it from entering the bloodstream where it can accumulate in the inner walls of arteries and set the stage for high blood pressure, heart disease, and strokes. Nutrition: Carbohydrates Insoluble fiber, found in vegetables, whole-grain products, and bran, provides roughage that speeds the elimination of feces, which decreases the time that the body is exposed to harmful substances, possibly reducing the risk of colon cancer. Studies of populations with fiber-rich diets, such as Africans and Asians, show that these populations have less risk of colon cancer compared to those who eat low-fiber diets, such as Americans. Nutrition: Carbohydrates In the United States, colon cancer is the third most common cancer for both men and women, but experts believe that, with a proper diet, it is one of the most preventable types of cancer. Nutritionists caution that most Americans need to eat more complex carbohydrates. Nutrition: Carbohydrates In the typical American diet, only 40 to 50 percent of total calories come from carbohydrates—a lower percentage than found in most of the world. To make matters worse, half of the carbohydrate calories consumed by the typical American come from processed foods filled with simple sugars. Nutrition: Carbohydrates Experts recommend that these foods make up no more that 10 percent of our diet, because these foods offer no nutritional value. Foods rich in complex carbohydrates, which provide vitamins, minerals, some protein, and dietary fiber and are an abundant energy source, should make up roughly 50 percent of our daily calories. "Human Nutrition," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved. IPS: Chemistry Review Atom- basic unit of matter Protons- positive charge, located in the nucleus Neutrons- neutral, located in the nucleus Electrons- negative charge, located outside the nucleus IPS - Chemistry Review Element- made of only one kind of atom. The number of protons determines what the element is called. In an atom, the number of protons and electrons are equal. The same element will always have a set number of protons. The number of neutrons may vary. These are called isotopes. Electrons may also vary. These are called ions. IPS - Chemistry Review The ion is determined by the number of electrons in the outer shell or orbit. These are called valence electrons. If an atom gains electrons, it becomes negatively charged. If an atom loses electrons, it becomes positively charged. IPS - Chemistry Review Bonds- joining two or more atoms together Ionic bond- formed by joining two ions together Example: NaCl Co-Valent bond-formed by the sharing of electrons Example: C6H12O6 Common molecules Macromolecules: Carbohydrates Carbohydrates made of C,H,O Sugar Starch The ratio of hydrogen to oxygen is 2:1 Cellulose Carbohydrates Sugar- manufactured in green plants. Provides the basic fuel for both plant and animal life. Carbohydrates Sugar Monosaccharides Mono = one saccharide = sugar Disaccharide Di = two Polysaccharide Poly = many Carbohydrates Sugar Monosaccharides- simple sugars that may contain 5 or 6 carbon atoms. Examples: Glucose, Fructose, Galactose These simple sugars are made in plant cells. They have the same empirical or molecular formula: C6 H12 O6. Their structural formulas are different. Monosaccharides Monosaccharides Glucose Fructose Galactose Monosaccharides Structural formulas allow you to visualize the molecule. Notice, even though these molecules all have the same number of each atom, they look different. Holt, Modern Biology Disaccharides Disaccharides Di = two Two simple sugars form one molecule of a double sugar. One molecule of water is given off. This is called a dehydration synthesis reaction. De = away hydro = water synthesis = put together Disaccharides Disaccharides Maltose Sucrose Lactose Disaccharides Glucose + glucose C6H12O6 + C6H12O6 maltose + water C12H22O11 + H2O Dehydration synthesis- take away water to put a molecule together Holt, Modern Biology Disaccharides Dehydration synthesis- take away water to put a molecule together Glucose + fructose sucrose + water C6H12O6 + C6H12O6 C12H22O11 + H2O Sucrose is common table sugar. It is found in sugar cane and sugar beets. Dehydration Synthesis Prentice Hall, Biology Review Disaccharides Dehydration synthesis- take away water to put a molecule together Glucose + galactose C6H12O6 + C6H12O6 lactose + water C12H22O11 + H2O Lactose is milk sugar, found in the milk of mammals. Disaccharides Can these reactions be reversed to break the disaccharide apart into two monosaccharides? Yes. What must be added? What is the process called? Water must be added. The process is called hydrolysis. Hydro = water lysis = break apart or to break down Disaccharides This is an example of Hydrolysis. Water is added to maltose in order to break it down into two glucose molecules. Of course, enzymes would control this process. Holt, Modern Biology Hydrolysis Prentice Hall, Biology Hydrolysis Prentice Hall, Biology Review Polysaccharides Polysaccharides are large molecules formed by joining monosaccharides. Poly = many How to Make a Polysaccharide Slap together three or more mono’s Keep on condensing (or dehydrating) (From a plant) Carbohydrates: Starch Starch is a polysaccharide made up of glucose units in branched chains. Each time a glucose molecule is added, one water molecule is removed (dehydration synthesis). There may be 500 to many thousands of glucose molecules joined to form a starch molecule. Examples: potatoes,corn, rice, wheat, and other grains. Carbohydrates Nutrition When we eat carbohydrates, the molecules are broken apart to form simple sugars. Water must be added for this process to occur (hydrolysis). Carbohydrates: Glycogen Glycogen is animal starch. It is made of highly branched chains of glucose molecules. It is produced in the liver and stored in the liver and muscles. When extra energy is needed, the liver converts glycogen into glucose. Polysaccharide: Glycogen (From an animal) Carbohydrates: Cellulose Cellulose is a large polysaccharide made of chains of glucose molecules. It may contain as many as 3,000 glucose molecules. Cellulose forms a strong fibrous structure in plant cell walls. It gives the walls support. Polysaccharide: Cellulose Lipids Carbohydrates Macromolecules Proteins Nucleic Acids Network Tree Starch Cellulose Glycogen Carbohydrates (C,H,O) 1 Sugar Monosaccharide Glucose 3+ Polysaccharide Galactose Fructose 2 Disaccharide Lactose Maltose Sucrose Monosaccharides Structural formulas allow you to visualize the molecule. Notice, even though these molecules all have the same number of each atom, they look different. Holt, Modern Biology Disaccharides: How are they put together? Dehydration synthesis- take away water to put a molecule together Glucose + glucose maltose + water Glucose + fructose sucrose + water Glucose + galactose C6H12O6 + C6H12O6 lactose + water C12H22O11 + H2O Dehydration Synthesis: What does it look like? Prentice Hall, Biology Disaccharides: How do we digest them? Hydrolysis. Water is added to maltose in order to break it down into two glucose molecules. Of course, enzymes would control this process. Holt, Modern Biology Compare and Contrast Starch Plants Glycogen Stored for later, converted into glucose for respiration.. Branched chains of glucose Big Animals Compare and Contrast Starch Branched chains Stored for later, converted into glucose for respiration. Cellulose Carbohydrates Polysaccharides glucose Big Straight Chains Found in plant cell walls Used for support Nutrition: Lipids Fat stored in the body cushions vital organs and protects us from extreme cold and heat. Fat consists of fatty acids attached to a substance called glycerol. Dietary fats are classified as saturated, monounsaturated, and polyunsaturated according to the structure of their fatty acids (see Fats and Oils). Nutrition: Lipids Fats, which provide 9 calories of energy per gram, are the most concentrated of the energyproducing nutrients, so our bodies need only very small amounts. Fats play an important role in building the membranes that surround our cells and in helping blood to clot. Once digested and absorbed, fats help the body absorb certain vitamins. Nutrition: Lipids Animal fats—from eggs, dairy products, and meats—are high in saturated fats and cholesterol, a chemical substance found in all animal fat. Vegetable fats—found, for example, in avocados, olives, some nuts, and certain vegetable oils—are rich in monounsaturated and polyunsaturated fat. As we will see, high intake of saturated fats can be unhealthy. Nutrition: Lipids To understand the problem with eating too much saturated fat, we must examine its relationship to cholesterol. High levels of cholesterol in the blood have been linked to the development of heart disease, strokes, and other health problems. Despite its bad reputation, our bodies need cholesterol, which is used to build cell membranes, to protect nerve fibers, and to produce vitamin D and some hormones, chemical messengers that help coordinate the body’s functions. Nutrition: Lipids We just do not need cholesterol in our diet. The liver, and to a lesser extent the small intestine, manufacture all the cholesterol we require. When we eat cholesterol from foods that contain saturated fatty acids, we increase the level of a cholesterol-carrying substance in our blood that harms our health. Nutrition: Lipids Cholesterol, like fat, is a lipid—an organic compound that is not soluble in water. In order to travel through blood, cholesterol therefore must be transported through the body in special carriers, called lipoproteins. High-density lipoproteins (HDLs) remove cholesterol from the walls of arteries, return it to the liver, and help the liver excrete it as bile, a liquid acid essential to fat digestion. For this reason, HDL is called "good" cholesterol. Nutrition: Lipids Low-density lipoproteins (LDLs) and very-lowdensity lipoproteins (VLDLs) are considered "bad" cholesterol. Both LDLs and VLDLs transport cholesterol from the liver to the cells. As they work, LDLs and VLDLs leave plaqueforming cholesterol in the walls of the arteries, clogging the artery walls and setting the stage for heart disease. Nutrition: Lipids Almost 70 percent of the cholesterol in our bodies is carried by LDLs and VLDLs, and the remainder is transported by HDLs. For this reason, we need to consume dietary fats that increase our HDLs and decrease our LDL and VLDL levels. Nutrition: Lipids Saturated fatty acids—found in foods ranging from beef to ice cream, to mozzarella cheese to doughnuts—should make up no more than 10 percent of a person’s total calorie intake each day. Saturated fats are considered harmful to the heart and blood vessels because they are thought to increase the level of LDLs and VLDLs and decrease the levels of HDLs. Nutrition: Lipids Monounsaturated fats—found in olive, canola, and peanut oils—appear to have the best effect on blood cholesterol, decreasing the level of LDLs and VLDLs and increasing the level of HDLs. Polyunsaturated fats—found in margarine and sunflower, soybean, corn, and safflower oils—are considered more healthful than saturated fats. However, if consumed in excess (more than 10 percent of daily calories), they can decrease the blood levels of HDLs. Nutrition: Lipids Most Americans obtain 15 to 50 percent of their daily calories from fats. Health experts consider diets with more than 30 percent of calories from fat to be unsafe, increasing the risk of heart disease. High-fat diets also contribute to obesity, which is linked to high blood pressure and diabetes mellitus. Nutrition: Lipids A diet high in both saturated and unsaturated fats has also been associated with greater risk of developing cancers of the colon, prostate, breast, and uterus. Choosing a diet that is low in fat and cholesterol is critical to maintaining health and reducing the risk of life-threatening disease. "Human Nutrition," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved. Macromolecules: Lipids Lipids are macromolecules made of carbon, hydrogen, and oxygen. The ratio of hydrogen to oxygen is much greater than 2:1. Lipids are made of fatty acids attached to alcohol. Examples: fats, oil, waxes and cholesterol. Macromolecules: Lipids Fat molecule = 3 fatty acid molecules plus one alcohol (glycerol). 3 Hydrogen ions are removed from glycerol and 1 hydroxide (OH) ion is removed from each fatty acid to make 1 fat molecule (C-O-C bonds are formed) + 3 water molecules. This process is called…. Dehydration Synthesis. Lipids Composed of fatty acids and glycerol Dehydration Synthesis of Fat Prentice Hall, Biology Lipids Excess food is stored as fat in animals. It is found in tissues and as butterfat in milk and other dairy products. Recall Carbohydrates, to answer the following: To break down the fat molecule to use it for energy, we would add ….., in the process called... Water…….Hydrolysis. Lipids: Triglycerides Useful for long-term storage of energy; warmth; organ protection (cushion) What reaction took place? Lipids: Phospholipids Cell membranes, remember? Lipids: Steroids Many animal hormones are steroids E.g., testosterone Lipids: Cholesterol Cholesterol is a large lipid molecule located in the cell membranes of animals. Cholesterol- needed by nerve cells In excess, it can form deposits on the inner walls of blood vessels making them less elastic and leaving less room for blood flow. Lipids: Unsaturated Fats Too much fat = bad (heart disease) Unsaturated better than saturated Unsaturated –> increase HDLs over LDLs Lipids: Oils/Waxes Oils Oils are lipids that are liquid at room temperature. Examples: vegetable oils such as, corn, peanut, soybean. Waxes Waxes are made of fatty acids joined to an alcohol other than glycerol. They are solid at room temperature. Nutrition: Proteins Dietary proteins are powerful compounds that build and repair body tissues, from hair and fingernails to muscles. In addition to maintaining the body’s structure, proteins speed up chemical reactions in the body, serve as chemical messengers, fight infection, and transport oxygen from the lungs to the body’s tissues. Nutrition: Proteins Although protein provides 4 calories of energy per gram, the body uses protein for energy only if carbohydrate and fat intake is insufficient. When tapped as an energy source, protein is diverted from the many critical functions it performs for our bodies. Nutrition: Proteins Proteins are made of smaller units called amino acids. Of the more than 20 amino acids our bodies require, eight (nine in some older adults and young children) cannot be made by the body in sufficient quantities to maintain health. These amino acids are considered essential and must be obtained from food. Nutrition: Proteins When we eat food high in proteins, the digestive tract breaks this dietary protein into amino acids. Absorbed into the bloodstream and sent to the cells that need them, amino acids then recombine into the functional proteins our bodies need. Nutrition: Proteins Animal proteins, found in such food as eggs, milk, meat, fish, and poultry, are considered complete proteins because they contain all of the essential amino acids our bodies need. Plant proteins, found in vegetables, grains, and beans, lack one or more of the essential amino acids. However, plant proteins can be combined in the diet to provide all of the essential amino acids. Nutrition: Proteins A good example is rice and beans. Each of these foods lacks one or more essential amino acids, but the amino acids missing in rice are found in the beans, and vice versa. So when eaten together, these foods provide a complete source of protein. Thus, people who eat only vegetables (see Vegetarianism) can meet their protein needs with diets rich in grains, dried peas and beans, rice, nuts, and tofu, a soybean product. Nutrition: Proteins Experts recommend that protein intake make up only 10 percent of our daily calorie intake. Some people, especially in the United States and other developed countries, consume more protein than the body needs. Because extra amino acids cannot be stored for later use, the body destroys these amino acids and excretes their by-products. Nutrition: Proteins Alternatively, deficiencies in protein consumption, seen in the diets of people in some developing nations, may result in health problems. Marasmus and kwashiorkor, both life-threatening conditions, are the two most common forms of protein malnutrition. Nutrition: Proteins Some health conditions, such as illness, stress, and pregnancy and breast-feeding in women, place an enormous demand on the body as it builds tissue or fights infection, and these conditions require an increase in protein consumption. For example, a healthy woman normally needs 45 grams of protein each day. Experts recommend that a pregnant woman consume 55 grams of protein per day, and that a breast-feeding mother consume 65 grams to maintain health. Nutrition: Proteins A man of average size should eat 57 grams of protein daily. To support their rapid development, infants and young children require relatively more protein than do adults. A three-month-old infant requires about 13 grams of protein daily, and a four-year-old child requires about 22 grams. Nutrition: Proteins Once in adolescence, sex hormone differences cause boys to develop more muscle and bone than girls; as a result, the protein needs of adolescent boys are higher than those of girls. "Human Nutrition," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved Macromolecules: Proteins Proteins are the most common organic molecule in living cells. They are made of carbon, hydrogen, oxygen, nitrogen and sometimes sulfer. CHON(S) Proteins are made of amino acids. There are approximately 20+ amino acids. Macromolecules: Proteins Proteins are large complex polypeptides. Prentice Hall, Biology Think of the amino acids as letters and proteins as words in making up a sentence. Proteins may contain as few as 50 or as many as 3,000 amino acid molecules. The number of possible combinations of amino acids is staggering. We have tens of thousands of different proteins. Macromolecules: Proteins Amino acids are joined by means of dehydration synthesis. An OH from the acid group of one amino acid joins to an H from the amino group of the other amino acid. A water molecule is formed, and a C-N bond is formed between the two amino acids. The C-N bond is called a peptide bind. Dipeptide: 2 amino acids joined Polypeptide: 3 or more amino acids joined. Proteins Composed of amino acids Amino acids are joined by peptide bonds The string of peptides is also called a polypeptide Needed for muscles, skin, cell membranes, and enzymes Proteins: Structure The protein you end up with depends on: which amino acids were chosen, their order (sequence), and how many of each Who decides? The DNA Proteins: Structure Amino acids have three parts: The 20+ amino acids differ only in their R-group Generalized Formula for Amino Acid H R C Acid group COOH NH2 Rest of the molecule Amino group Amino Acid Groups H NH2 = N H O COOH = C O H Macromolecules: Proteins Proteins taken in as food are different than our proteins. They must be broken down into amino acids by adding water. Recall Carbohydrates and Lipids The process is… Hydrolysis. To build proteins water must be removed in the process of…. Dehydration Synthesis. Dehydration Synthesis Prentice Hall, Biology Proteins: Structure Compare 3 amino acids: Category 1 Category 2 Let’s Review What is the name of this unit? Category 3 Category 4 Proteins: Enzymes Enzyme, any one of many specialized organic substances, composed of polymers of amino acids, that act as catalysts to regulate the speed of the many chemical reactions involved in the metabolism of living organisms. The name enzyme was suggested in 1867 by the German physiologist Wilhelm Kühne (1837-1900); it is derived from the Greek phrase en zymç, meaning "in leaven.” Those enzymes identified now number more than 700. Proteins: Enzymes Enzymes are classified into several broad categories, such as hydrolytic, oxidizing, and reducing, depending on the type of reaction they control. Hydrolytic enzymes accelerate reactions in which a substance is broken down into simpler compounds through reaction with water molecules. Proteins: Enzymes Oxidizing enzymes, known as oxidases, accelerate oxidation reactions; reducing enzymes speed up reduction reactions, in which oxygen is removed. Many other enzymes catalyze other types of reactions. Proteins: Enzymes Individual enzymes are named by adding ase to the name of the substrate with which they react. The enzyme that controls urea decomposition is called urease; those that control protein hydrolyses are known as proteinases. Some enzymes, such as the proteinases trypsin and pepsin, retain the names used before this nomenclature was adopted. Proteins: Enzymes Some enzymes, such as pepsin and trypsin, which bring about the digestion of meat, control many different reactions, whereas others, such as urease, are extremely specific and may accelerate only one reaction. Still others release energy to make the heart beat and the lungs expand and contract. Proteins: Enzymes Many facilitate the conversion of sugar and foods into the various substances the body requires for tissuebuilding, the replacement of blood cells, and the release of chemical energy to move muscles. Proteins: Enzymes As a class, enzymes are extraordinarily efficient. Minute quantities of an enzyme can accomplish at low temperatures what would require violent reagents and high temperatures by ordinary chemical means. About 30 g (about 1 oz) of pure crystalline pepsin, for example, would be capable of digesting nearly 2 metric tons of egg white in a few hours. Proteins: Enzymes The kinetics of enzyme reactions differ somewhat from those of simple inorganic reactions. Each enzyme is selectively specific for the substance in which it causes a reaction and is most effective at a temperature peculiar to it. Although an increase in temperature may accelerate a reaction, enzymes are unstable when heated. Proteins: Enzymes The catalytic activity of an enzyme is determined primarily by the enzyme's amino-acid sequence and by the tertiary structure—that is, the threedimensional folded structure—of the macromolecule. Many enzymes require the presence of another ion or a molecule, called a cofactor, in order to function. Proteins: Enzymes As a rule, enzymes do not attack living cells. As soon as a cell dies, however, it is rapidly digested by enzymes that break down protein. The resistance of the living cell is due to the enzyme's inability to pass through the membrane of the cell as long as the cell lives. Proteins: Enzymes When the cell dies, its membrane becomes permeable, and the enzyme can then enter the cell and destroy the protein within it. Some cells also contain enzyme inhibitors, known as antienzymes, which prevent the action of an enzyme upon a substrate. "Enzyme," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved. Proteins: Enzymes Enzymes are proteins that act as a catalyst. (Catalysts are substances that increase the rate of a chemical reaction.) Enzymes are not used up or changed by a reaction. Enzymes are specific in their actions. Enzymes work best under specific conditions. Substrate: The substance that the enzyme causes to react. Enzymes Nucleic Acids: DNA 4. Nucleic Acids DNA or RNA Composed of nucleotides Each nucleotide has a Phosphate group Sugar (deoxyribose or ribose) Nitrogen base 4 bases A, G, C, T (or U in RNA) Who am I?