2.0 Biology HP Chemistry of Life

Chloride ions are important to cell balance.

A Kansas farmer walking through his field bends down and picks up a cimarron plant covered in yellow spots. He shakes his head, knowing what the spots on this plant mean—the soil is deficient in chloride ions. You have learned about several positively charged ions—calcium (Ca2+), sodium (Na+), and potassium (K+). Chloride is a negatively charged ion that living things need. Chloride ions (Cl-) have many functions in plants. They are vital in the opening and closing of stomata—structures on the underside of leaves that allow gas exchange. They are also involved in the uptake of nitrogen and in the balance of fluids throughout the plant. In animals, chloride ions are most often present in the fluid outside of the cells and in the blood. They play similar roles to their positively charged partners, and together they move back and forth, balancing blood volume, blood pressure, cellular fluids, and pH. The bottom leaves of this cimarron plant show classic chloride ion deficiency.

2.02 Chemical Bonds Atoms form bonds by losing, gaining, or sharing electrons. (The picture shows that Sodium has one valence electron on the outer ring.

A chemical bond is a force that holds atoms together. When two or more atoms bond together, they form molecules Opens in modal popup window , substances, or compounds. To understand how atoms bond, you need to know more about the tiniest part of an atom—the electron. Electrons move around the nucleus of an atom in different levels. The electrons in the outer level of an atom are called valence electrons Opens in modal popup window . When two or more atoms bond, they lose, gain, or share valence electrons. Turn to page 20 in your reference book to review the structure of some key atoms of the living world. Note the different levels of electrons in each atom, including the valence electrons.

Calcium triggers a release of energy in certain protein molecules.

A deep-sea research vessel is scanning uncharted depths of the ocean. A glow appears in the inky depths ahead of the vessel, and an anglerfish comes into view dangling a luminescent lure. The glowing lure is part of the fish's body. How does the fish produce light? It comes from a protein that is activated in the presence of calcium (Ca). Bioluminescence —light produced by a living organism—is caused by a chemical reaction that transforms chemical energy into light energy. The glow of an anglerfish's lure is the product of a chemical reaction that occurs when calcium ions activate a certain kind of protein.

Vitamin B12 is an organic compound that contains cobalt.

A female panda is about the same length as the average woman—between 1.5 and 1.8 m (5 and 6 ft), but her newborn is no larger than a chipmunk. She cares for her pint-size infant carefully, making sure it gets the milk it needs to grow and be healthy. Milk is a rich source of vitamin B12. No doubt you've heard how important it is to get enough vitamins in your diet. Perhaps you take vitamin pills every day. Vitamins are essential nutrients. Vitamin B12 helps in the development of healthy red blood cells, which use hemoglobin to carry oxygen to cells. B12 is also significant because it helps maintain parts of the nervous system. A key part of vitamin B12 is the element cobalt (Co). Your body needs cobalt in very small amounts, and gets it when you drink milk and eat poultry, meat, and fish.

Proteins help organisms respond to the environment.

A frog sees an insect fly by. In a flash, the frog's legs bound into action as it leaps up toward the insect. The frog's leg muscles are moving under the direction of proteins called actin and myosin, which work together to cause muscles to contract and move. These are just two of thousands of examples of proteins that play a role in helping organisms respond to their environment. Another class of proteins that help organisms maintain homeostasis is receptor proteins. This diverse group of proteins is typically found in cell membranes that recognize and bind to specific molecules such as hormones, which are chemical signals released by the nervous system. Other proteins help transport materials across the lipid bilayer of cell membranes.

Some medicinal compounds come from plants that are poisonous in their natural state.

A group of young children run through a field in England punctuated with colorful wildflowers. They approach a tall plant with pinkish blooms hanging upside down on a stalk, and they admire its beauty. As beautiful as it is, the plant in its natural state is poisonous. The plant, called foxglove, contains the potent chemical digoxin Opens in modal popup window . Digoxin is both a poison and a medicine. It is the active ingredient in digitalis —a heart medication used by millions of people. Proper amounts of digoxin, a large organic molecule, can be broken down in the body into another compound called digitoxin. Digitoxin stimulates the heart, causing it to beat faster and circulation to improve. Better circulation keeps heart patients from retaining too much fluid, a common side effect in people with a weak heart rate. Foxglove is an example of a plant that can have both helpful and harmful effects. Physicians have to be extremely careful with dosage because a slight overdose can be fatal. Foxglove is a poisonous plant that contains digoxin, an active ingredient in the heart medication digitalis.

Hydrogen ions are used in aerobic respiration and to maintain the balance of acids and bases.

A monarch butterfly weighs about 0.5 g, but this fragile animal can fly from the United States to its wintering home in Mexico—about 3,220 km (2,000 mi). Where does something so small get the strength to fly that far? Deep within the monarch's cells, large quantities of the energy-donating chemical adenosine triphosphate (ATP) are produced. A complex process takes place within the cells to make this energy available. Near the end of the process, hydrogen ions (H+) play an important role. Without hydrogen ions, ATP could not be generated. Hydrogen ions are also central players in maintaining an acid-base balance in an organism. It readily binds to other compounds, helping keep the levels of acids and bases regulated. Without hydrogen ions, the monarch's cells could not generate the energy-donating compound ATP.

Demand for ATP

A muscle's ATP demands, even when performing a simple motion, are enormous: A single muscle cell can use up to 1 million molecules of ATP every second. All the cells in your body use about 100,000,000,000,000,000,000 (1020) ATP molecules every second.

The cell membrane is a phospholipid bilayer.

A phospholipid s similar to a fat: It contains fatty acid chains and glycerol. However, a phospholipid contains only two fatty acid chains, while a fat contains three. It also includes a chemical structure called a phosphate group. A phosphate group gives one end of a phospholipid a negative electrical charge—that is, this end of the chain is hydrophilic because it attracts water molecules. As you learned earlier, the fatty acid chain is nonpolar and repels water. What might happen, then, when you put phospholipids in water? In a watery environment, phospholipids arrange themselves so that the fatty acid chains (hydrophobic tails) point inward toward each other, while the phosphate groups (hydrophilic heads) point out, interfacing with the water. This interaction creates two layers of phospholipids-a bilayer. The phospholipid bilayer makes up the outer membrane of all the cells in your body. Because of its unique structure and chemical properties, the phospholipid bilayer can contain a separate internal aqueous environment, relative to the outside.

2.16 Levels of Protein Structure Proteins have four levels of structure.

A strand of hair might not look very complicated, but at the molecular level, it certainly is. Hair is made of the protein keratin, and like all proteins, keratin has a structure consisting of folds, twists, and kinks that is held together by a variety of chemical bonds. A protein is a large molecule made of two or more polypeptide chains. Each polypeptide is made up of chains of amino acids—molecules composed of a carbon, hydrogen, nitrogen, and oxygen backbone. Proteins are defined by four structural levels, starting with the order of amino acids that make up the polypeptide chain and continuing up to the interactions of the chains themselves. You'll learn more about each level of structure throughout this lesson.

E-85

A type of fuel called E-85, available at gas stations across the Unites States, contains a blend of gasoline and ethanol, which is a chemical made by breaking down the starch in corn.

Lipids are mainly nonpolar and hydrophobic.

A typical lipid consists of a long chain of carbon atoms flanked by hydrogen atoms. Sometimes the end of the chain contains atoms other than carbon and hydrogen. The oil on a loon's feathers is hydrophobic, or water avoiding. The oil's molecular structure gives it that property—the long tail of the molecule is not electrically charged; it is neither positive nor negative. In other words, this portion of the lipid is nonpolar. These electrically neutral tails are not attracted to polar molecules like water, which have a slightly negative side and a slightly positive side. But, as you might suspect, the polar head of the lipid, which you can see in the diagram, is attracted to polar water molecules. The properties of polarity and nonpolarity play an important role in how lipids function in the body, especially in their formation of cell membranes.

2.12 Simple Carbohydrates Carbohydrates are organic compounds made from carbon, hydrogen, and oxygen.

A wild rabbit digs a hole under a garden fence. Inching through, it feasts its eyes on fresh lettuce, carrot tops, and cauliflower buds. Soon after, its belly full, it struggles to escape nearby footsteps. The rabbit has just dined on a buffet of carbohydrates. Carbohydrates Opens in modal popup window are a class of organic compounds made exclusively from carbon, hydrogen, and oxygen. The atoms are in a general ratio of 1:2:1, which means there are an equal number of carbon and oxygen atoms, and twice as many hydrogen atoms, in every carbohydrate. Carbohydrates are a class of organic compounds made exclusively from carbon, hydrogen, and oxygen.

ATP is a complex organic molecule that provides energy for life processes such as growth, development, and response to the environment. ATP provides chemical energy to drive chemical reactions for the cell.

ATP is often called the currency of energy transfer in living organisms. When scientists say this, they mean that ATP is a source of usable energy or energy that organisms can use to do work, such as moving muscles or carrying substances across cell membranes. The molecule ATP contains energy in its chemical bonds; it gives up energy when the bonds between its phosphate groups break. ATP is both produced by and used in cells. When ATP breaks down into ADP, it is eventually built back up to ATP in a process that recycles the molecules in your body over and over.

Many cellular processes require ATP. Cyanide is a deadly poison that stops the production of ATP in cells, shutting off all energy.

ATP is required for all life processes. Cells use ATP to help move molecules, ions, and other substances across their cell membranes. Some substances can flow freely across a cell's phospholipid bilayer, but many times, depending on the cell's environment, energy may be required to bring substances into a cell or to carry substances out of a cell. This process is known as active transport, and you will learn more about it in the next unit. Cells use ATP for thousands of chemical reactions. A breakdown in the ATP production process will kill a cell. For example, the poison cyanide works to shut down the cell processes that make ATP. Cyanide is a deadly poison because it shuts off all available energy to the cell. Turn to page 56 in your reference book for more details about the process of moving materials across cell membranes.

ADP to AMP

Additional reactions can further break down ADP by removing yet another phosphate group and producing the molecule adenosine monophosphate (AMP). In some single-cell organisms, AMP plays a role in intercellular communication and movement.

2.14 Lipids Lipids are organic molecules that do not mix with water to form solutions.

After a loon dives underwater to hunt fish, it pops up to the surface, and beads of water run down its neck and back. Why doesn't the loon sink under the weight of the water? Why does water roll right off its body? Loons produce an organic molecule called oil in a special gland near the base of their tail. They use their beak to extract oil from this gland and work it through their feathers, giving them an effective waterproof coating. The oil that waterproofs a loon's feathers is one example of a lipid , a type of organic molecule that generally repels water. Lipids are hydrocarbons a class of organic molecules that are made almost entirely of hydrogen and carbon. Turn to pages 38 and 39 of your reference book for additional information as you complete this lesson. Loons produce an oil that forms a waterproof coating on their wings.

2.07 Water Living things depend on water in many ways.

After weeks of drought, animals in the desert around Tucson, Arizona, are stirred to action at the approach of rain. A mule deer nuzzles her thirsty fawn as thick, humid air moves in. Then, drop after drop of life-sustaining water begins to fall from the clouds. As the rain pours down, the desert reawakens. Water is essential for life. As you will see, water is also chemically unique. No other substance on earth compares to water's abilities, properties, and characteristics.

Waxes repel water.

Agave, ocotillo, and cactus are familiar plants of the Sonoran Desert in southwestern Arizona and northern Mexico. Like all living organisms, those plants require water to survive, yet they live in one of the driest places on earth. How do they retain that water and keep it from evaporating? They cover their leaves in a water-repelling substance that keeps water from getting to the surface where it might evaporate. One feature common to these plants and others is a waterproof coating called wax. Wax is a type of lipid made of extremely long chains of fatty acids linked to an alcohol molecule. The fatty acids in waxes are saturated, meaning they form long chains that pack well together. Fatty acid chains are nonpolar, so they do not attract water, which makes waxes hydrophobic or water-repellent. Many plants cover themselves in wax, a type of lipid made of extremely long chains of fatty acids linked to an alcohol molecule.

Simple carbohydrates are often used as a source of energy. Simple carbohydrates include monosaccharides are made up of one sugar molecule include glucose, fructose, and galactose. Simple carbohydrates include disaccharides are made up of two sugar molocules include sucrose and lactose.

All carbohydrates contain carbon, hydrogen, and oxygen in a ratio of 1:2:1. The building blocks of carbohydrates are single sugar molecules. Monosaccharides and disaccharides are simple carbohydrates made of one or two sugars, respectively. Simple carbohydrates may bond to one another to make complex carbohydrates, which are the focus of the next lesson. The body converts proteins, fats, and carbohydrates into glucose, which is broken down in a series of reactions to produce usable energy for cells.

Aspirin is made from a natural compound in willow trees.

Americans reach for aspirin about 80 million times a year. Aspirin is the most widely used synthetic drug, and it is derived from willow trees. The ancient Greeks and Native American peoples used bark from willow trees as a pain reliever. Aside from reducing pain, people also use aspirin to lower fevers, halt inflammation, and even reduce the risk of heart attacks and strokes. The chemical compound responsible for these benefits is salicylic acid (C7H6O3). It works by interrupting a chemical reaction within cells that produces a kind of molecule found in people experiencing pain or inflammation. Salicylic acid prevents the chemical reaction from taking place and rids the body of the unwanted molecules.

Amino acids share a chemical backbone of carbon, hydrogen, nitrogen, and oxygen.

Amino acids are a class of organic compounds that contain carbon (C), hydrogen (H), nitrogen (N), and oxygen (O). All amino acids have a central carbon atom with four components attached to it. Three of these components are identical in all amino acids: a single hydrogen atom; an amino group that consists of a nitrogen atom and two hydrogen atoms; and a carboxyl group that consists of a carbon atom bonded to two oxygen atoms, one of which also bonds to a hydrogen atom. The fourth unit connected to an amino acid is called an R-group, which is sometimes referred to as a side chain. The R-group is different in different amino acids. Its chemical and physical properties give each amino acid unique characteristics and functions. Turn to page 32 of your reference book for more information on proteins. All amino acids have a central carbon atom with four comonents attached to it.

Some natural substances can be dangerous if misused.

An elderly Chinese woman struggles to breathe as she lies on her floor mat. Her daughter brings her a tea made from Ephedra sinica, a plant that grows abundantly near their home. Soon the woman begins to breathe more easily. Powerful compounds made from ephedra plants have been used successfully for several thousand years to treat respiratory ailments. But the compounds can also be misused. In 2004, the FDA banned the use of ephedrine, the active chemical, in all over-the-counter products. Studies show that the risks of taking ephedrine may outweigh the benefits. Debate on the use of the drug continues. Ephedrine is an example of a natural compound that can be harmful if not used correctly. Once a popular dietary supplement for weight loss, ephedrine is now a restricted substance because of health concerns. Today, doctors prescribe ephedrine only in low doses for asthma, colds, allergies, and a few other conditions. To learn more about the FDA's ruling on ephedrine, visit the FDA online.

Lactose is a common disaccharide found in milk products.

An inconspicuous opening on a cliff in Thailand is home to a community of bumblebee bats-one of the most endangered species on earth. At less than 2 g each (lighter than a dime), more than a hundred frail baby bats clutch their inverted mothers, suckling their rich milk. Fueling the growth of their miniature bodies is a disaccharide commonly found in milk products called lactose. All mammals produce lactose Opens in modal popup window for their offspring in the form of rich milk. Also called milk sugar, lactose is formed when a glucose molecule and a galactose molecule form a chemical bond.

Atoms bond together to form molecules, compounds, and substances.

An ion is an atom that has gained or lost an electron, and is therefore carrying an electrical charge. In an ionic bond, atoms lose or gain electrons. They are drawn together because their opposite electrical charges attract. In a covalent bond, which is the strongest type of bond, atoms share their valence electrons. Hydrogen bonds occur between partially charged molecules where a hydrogen atom is involved. Despite the apparent order of atomic bonding, matter tends toward unorganized states or entropy.

Sodium is vital to the balance of water in cells.

An organism's cells are filled with fluid, and they are also bathed in fluid. The balance of water moving into and out of cells is critical to the survival of any living thing. Too much water in the cells causes them to rupture. Too little water and they cease to function. Sodium ions (Na+) play an important role in balancing the movement of fluids into and out of cells. When marine iguanas swim in the ocean in search of food, they take in a lot of sodium ions and chlorine ions—more than their bodies can tolerate. They deal with the excess ions in a unique way. The excess sodium ions and chloride ions accumulate in glands near the iguanas' nostrils, where they form solid salt. To rid their bodies of the salt, the iguanas simply sneeze it out. Marine iguanas sneeze to rid their bodies of excess sodium ions and chloride ions to keep their body cells healthy.

Fructose is a common monosaccharide found in fruits.

As first light emerges on a dense canopy, a monkey wakes the forest with his resonating call. He has discovered some ripe fruit. Following his lead, his troop descends on the fruit, indulging in the plump, rich, juicy treats. Across the planet, a human family is on a picnic; they sink their teeth into luscious, dripping peaches. Both primates enjoy the sweetness of fructose, an aromatic monosaccharide often produced in fruits. Surprisingly enough, it has the same chemical formula as glucose, but exists in a different structural form. Click on the piece of fruit to compare the chemical formulas and the chemical structures of those two monosaccharides. A simple difference in structure results in notable differences between glucose and fructose. After being ingested, fructose is converted into glucose so that it can enter energy-generating reactions.

An enzyme's structure is responsible for its binding properties.

As you've learned, the structure of a protein influences its function. It should come as no surprise to learn that this relationship applies to enzymes, as well. The overall shape, structure, and chemistry of an enzyme are what accounts for its specificity. The molecule that an enzyme interacts with is called the substrate, and the region of the enzyme that recognizes the substrate is called the active site. The active site often appears as a groove or indentation on the surface of the enzyme, into which the substrate fits. Substrate molecules bind to an enzyme's active site to produce an enzyme-substrate complex. Once bound, the enzyme shifts its shape slightly, bringing its peptide chains in closer contact with the substrate molecule, much like a catcher's mitt clasping a baseball.

Aspirin and Children

Aspirin products carry a warning label stating that children under 16 should not take aspirin without the advice of a doctor. Recent studies have linked salicylic acid to Reyes syndrome, a rare but serious disease in young children. Most doctors now prescribe products containing acetaminophen instead of salicylic acid to treat common childhood illnesses like colds and fever.

All atoms have a similar overall structure.

Atoms are made up of three kinds of particles: protons, neutrons, and electrons. At the center of every atom is a nucleus. Protons Opens in modal popup window make up part of the nucleus. Protons have a positive electrical charge. Neutrons Opens in modal popup window are part of the nucleus, too. Neutrons have neither a positive nor a negative electrical charge. Moving at nearly the speed of light around the nucleus are small particles called electrons Opens in modal popup window . Electrons have a negative electrical charge.

Atoms bond and become more stable.

Atoms have electrons that orbit a nucleus, and the electrons move in different levels. Here's a new twist: Each level can hold only a certain number of electrons. Hydrogen (H) and helium (He) can hold a maximum of 2 electrons in their outer level. Most other atoms can hold up to 8. An atom is not stable until its outer level contains the maximum number of electrons. If the outer level of an atom holds fewer than the maximum number of electrons, the atom will undergo changes until its outer level is full. Then the atom is more stable. Table salt forms from an ionic bond between sodium and chlorine atoms. Review the formation of an ionic bond.

Carbon can bond to form different-shaped molecules.

Because carbon has 4 valence electrons, it can bond easily with other atoms. It can also bond with other carbon atoms. This makes it particularly suited for forming many different molecules. Those molecules can take several shapes. In these examples, the first structure is called a straight chain. The second structure is a branched chain. The third structure is a ring. Carbon atoms have bonded with each other to form these molecules. Four large carbon-based molecules known as macromolecules are present in all living things: carbohydrates, lipids, proteins, and nucleic acids. Carbon atoms bond together to form molecules with several shapes.

Aloe vera plants contain compounds that may have health benefits.

Bright blue skies and palm trees swaying in the breeze—you are vacationing in the Mediterranean with your family. You enjoy a long day at the beach riding waves and collecting seashells. Later that afternoon, you realize your skin is thoroughly sunburned. You walk down to the street market to seek help. A woman takes you into her shop and breaks open the spongy, green leaf of a plant. A thick gel oozes out, and she motions for you to rub it onto your burned skin. You feel immediate relief. Many people use the plant called aloe vera to treat various skin conditions. The U.S. Food and Drug Administration (FDA) has not ruled on the plant's effectiveness, and scientific studies continue.

The sequence of nitrogenous bases in one strand of DNA determines the sequence in the other.

By knowing the identity of one nitrogenous base in a molecule of DNA, you can predict the identity of its pair in the opposing strand. In other words, the sequence of one strand determines the sequence of the other. The sequence of bases in a DNA molecule contains the information that organisms need to build proteins and carry out many important life processes. You'll learn more about how DNA contains that information in a future lesson.

Carbon plays a central role in the molecules of all living things. Carbon atoms have 4 valence electrons that bond readily to other atoms to form organic compounds.

Carbon has 4 valence electrons, but it needs 8 to be stable. With 4 available spaces for electrons in its outer shell, a carbon atom easily forms covalent bonds with common atoms like hydrogen and oxygen. This unique characteristic makes carbon extremely versatile, so it is often the base element or backbone in a chemical compound. Carbon is present in all molecules critical to living things—proteins, fats, carbohydrates, and nucleic acids. Carbon is also present in nonliving things.

Your genetic material—the material in your body that determines the color of your eyes and hair, your bone structure, and so forth—is made of molecules called nucleic acids. There are two basic types of nucleic acids—deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Molecules like adenine, which contain carbon, are an important part of the structure of DNA and RNA.

Carbon is present in nucleic acids.

Most animals cannot digest cellulose.

Cellulose contains the same fundamental molecule—glucose—as starch, but the two complex carbohydrates have very different properties. Most animals cannot use cellulose as a source of energy, because they do not have the enzymes required to break the bonds holding the molecule together. Cellulose, however, is still an important part of your diet. How can this be if it can't be broken down for energy? Cellulose is sometimes called dietary fiber. Have you ever been told to eat at least five servings of fruits and vegetables every day? In addition to many important nutrients, fruits and vegetables are excellent sources of dietary fiber. Just think of all the cell walls in a serving of spinach. Cellulose is an important part of your diet specifically because it is not digested. It passes through your digestive system and helps your system function effectively.

2.01 Chemistry Review Everything that exists, living and nonliving, is made of chemicals.

Certain chemical elements are essential to every living thing. To understand life, you need a basic understanding of chemistry.

Complex carbohydrates provide energy storage and structure for living organisms.

Complex carbohydrates are large molecules made of many molecules of glucose linked together. Like glucose, complex carbohydrates are made of the elements carbon, hydrogen, and oxygen. Starch and glycogen are complex carbohydrates that provide a way for organisms to store energy in their cells. The complex carbohydrate cellulose functions as a structural material in plants. But unlike starch and glycogen, few organisms can digest cellulose.

DNA is a double-stranded molecule in the shape of a twisted ladder.

DNA contains the genetic blueprints that your body needs for growth and development. When the cells in your body divide, the DNA in your cells divides, too—a process called replication—producing an identical copy of DNA for newly formed cells. You'll learn more about this process in a future lesson. A DNA molecule forms when two strands of nucleotides link together and twist around each other, like a ladder that has been twisted. This structure is called a double helix. Turn to page 41 in your reference book, and note how the sugar-phosphate backbone forms the outside of the double helix. The sugar in DNA is called deoxyribose, from which DNA gets its full name: deoxyribonucleic acid.

Elements differ based on the number of protons in their atoms. Carbon (C): 6 protons, 6 neutrons, 6 electrons Nitrogen (N): 7 protons, 7 neutrons, 7 electrons Oxygen (O): 8 protons, 8 neutrons, 8 electrons

Different elements have a different number of protons in their atoms. An atom of carbon always has 6 protons. The number of protons is the element's atomic number. A carbon atom has 6 protons, so its atomic number is 6. Every element has a specific atomic number. For example, nitrogen atoms have 7 protons, so nitrogen's atomic number is 7. Oxygen atoms have 8 protons, so oxygen's atomic number is 8. Look at pages 18-19 in your reference book again and notice the atomic numbers of the elements in the Periodic Table.

Most starch molecules have a branching structure.

Different types of plants make different types of starches. For example, potato starch is slightly different from the starch found in corn or beets—each type of starch consists of a different number of glucose molecules. Different starches also may show different patterns of branching, in which one chain of glucose molecules branches off of another. This type of branching structure relates to the function of starch as a storage molecule. In times of energy shortage, enzymes attack the ends of the starch molecule, releasing glucose molecules one at a time for use by cells. Branches of glucose chains provide more ends where the enzyme can break down, or digest the starch, thus quickly releasing more glucose molecules. Those molecules are then available to enter the process of cellular respiration, which breaks down glucose into usable chemical energy. In this illustration, each dot represents a glucose molecule.

2.17 Proteins as Enzymes Enzymes are proteins that speed up chemical reactions.

Do you know anybody who is lactose intolerant? People with that condition cannot digest the disaccharide lactose, which is found in dairy products. They can't digest this sugar because their bodies lack an enzyme called lactase, which breaks apart the lactose molecule. The enzyme lactase is a catalyst, a compound that changes the speed of a chemical reaction without itself being changed by the reaction. Lactase acts to catalyze the breaking of the bond that holds together the two monosaccharides—galactose and glucose—that make up lactose. Lactase is a protein; enzymes are proteins, but not all proteins are enzymes. Breaking apart the disaccharide lactose molecule into two monosaccharide molecules makes it possible for the body to digest a milk product. The full lactose molecule is difficult for the body to absorb, and lactose-intolerant individuals can experience abdominal cramps and other symptoms from consuming too much lactose.

When hydrogen bonds with a larger atom, the electrons are shared unevenly.

Do you know the game tug-of-war? Imagine the covalent bond between hydrogen and oxygen as the rope in a tug-of-war, and each side is pulling to win over their shared electrons. The tiny hydrogen atoms, each with 1 positively charged proton, are no match for the larger oxygen atom with 8 protons. The negatively charged electrons stay a little closer to the oxygen atom because of its stronger positive charge. The result? The oxygen atom takes on a slight negative charge from being closer to all of those electrons, and the hydrogen atoms take on a slight positive charge from being farther away.

Simple carbohydrates are often used as a source of energy.

Each cell of this manatee's body requires usable energy to function. The plants it is munching on contain loads of carbohydrates—the source of the manatee's energy. Living things use carbohydrates—specifically, the monosaccharide glucose—as a source of chemical energy. After ingesting them in various forms, living things digest and break down carbohydrates through a series of chemical reactions. A cow might eat grass, a hawk might eat a mouse, and a bacterium might decompose part of a dead mouse. In all cases, the food is ultimately broken down into glucose, the monosaccharide that provides chemical energy for the living thing. Manatees, like all living things, use carbohydrates as a source of chemical energy.

The electrical charge of an atom can change. Carbon (C) +6 protons -6 electrons =0 electrical charge

Electrons are much smaller than protons, but their negative charge is as strong as a proton's positive charge. An atom that has the same number of electrons and protons has a neutral electrical charge, or no charge. Atoms routinely lose, gain, and share electrons. If an atom loses an electron, the atom will then have a positive electrical charge. If an atom gains an electron, the atom will then have a negative electrical charge. Atoms that have an electrical charge are called ions Opens in modal popup window .

Enzymes lower a reaction's activation energy.

Energy is required for all chemical reactions that take place in your body. The amount of energy required for a reaction to take place is called activation energy. A system needs to overcome that energy barrier for a reaction to take place. Enzymes speed up chemical reactions by lowering activation energy. Enzymes lower activation energy of reactions in many ways. For example, bringing molecules together in just the right way helps lower the amount of energy that would otherwise have been required for a bond to form if those molecules were moving about freely in intracellular space. Scientists often display the concept graphically, with the activation energy Opens in modal popup window as a hill a reaction needs to ascend before the reaction can take place. Here are examples of graphs that may help you understand activation energy. You can also find these graphs on pages 36 and 37 of your reference book.

Enzymes are proteins that speed up reactions but do not change themselves.

Enzymes are a class of proteins that act as catalysts, or compounds that speed up chemical reactions. They may do so in several ways, including bringing molecules closer together, as well as making or breaking bonds between molecules. Enzymes reduce the activation energy required for a chemical reaction to take place. Environmental conditions, such as changes in pH or temperature, affect enzyme activity.

More than 300 types of enzymes contain zinc.

Enzymes are organic compounds that help chemical reactions in living things take place efficiently. Picture two compounds randomly floating around. They may never interact. An enzyme makes the interaction happen. Zinc (Zn) atoms are a part of more than 300 different enzymes. One of those enzymes is called carbonic anhydrase. When you eat, the strong acids in your stomach break up the food into smaller particles. The acid balance in your stomach must stay within acceptable levels. If it doesn't, you could develop indigestion. Carbonic anhydrase helps maintain the balance of acid in your stomach. Zinc is a key part of that enzyme. You will learn more about enzymes later in this unit. The enzyme carbonic anhydrase, which contains zinc (Zn), helps maintain the stomach's acid balance.

Enzyme-assisted reactions reach a maximum rate. A single enzyme molecule can interact with thousands of substrate molecules every second.

Enzymes play an important role in speeding up many chemical reactions that are essential for life, but the rate of those reactions eventually reaches a maximum point. That point occurs when all available enzymes are bonded to substrate molecules. At that point, the enzymes are said to be saturated. When the concentration of substrate molecules is low, adding more of those molecules speeds up the reaction rate, because more molecules are available to interact with the available enzymes. Once the enzymes are saturated, the reaction doesn't proceed any faster: It's at its maximum rate. Can you identify the saturation point in the illustration on the left?

Water is a polar molecule.

Even your little brother probably knows that H2O is water. What he likely doesn't know is what a water molecule looks like. Water molecules are shaped something like miniature boomerangs—they're bent. The hydrogen atoms line up at an angle to the oxygen atom. Remember the water molecule in the lesson on chemical bonds? A water molecule has 2 hydrogen atoms (H) covalently bonded to 1 oxygen atom (O). The large oxygen atom with its 8 protons pulls more strongly on the shared electrons than the hydrogen atoms do. The electrons are more often located nearer the oxygen atom than the hydrogen atoms. This arrangement gives the oxygen atom a slight negative charge and the hydrogen atoms a slight positive charge. This type of molecule—one that has an unequal distribution of electrical charges—is a polar molecule.

Living things are composed mostly of water.

Every cell of a living thing is like a water-filled factory, providing the perfect medium for all life processes to take place. It is at the cellular level that the most critical reactions occur: the formation of proteins, the transmission of chemical messages, and the generation of usable chemical energy. In addition, materials in living things are circulated and transported by water-based fluids. The process of reproduction more often than not depends on water. Every cell of a living thing is like a water-filled factory.

All matter, living and nonliving, is made of elements and atoms.

Everything in the universe is matter, and matter is made of elements. Some elements are essential to living things. Elements are made of atoms, and atoms are composed of protons, neutrons, and electrons. The number of protons in an element's atoms determines the identity of the element.

Scientists have different ways of representing atoms and the chemical compounds they form.

Explore the activity onscreen to learn more ways of representing atoms and molecules. In the model of methane, each black line represents the pair of electrons that are shared between the central carbon atom (C) and the hydrogen atoms (H) in each hydrogen bond. In the carbon dioxide molecule (CO2), note that a carbon atom shares 2 valence electrons with each oxygen atom (O). Each oxygen atom shares 2 valence electrons with the carbon atom. The double lines in the carbon dioxide model represent the two pairs of shared electrons in each covalent bond.

Fats and oils store energy in carbon-hydrogen bonds.

Fats and oils (like butter, lard, and olive oil) are types of lipids called triglycerides. Triglycerides comprise two types of chemical building blocks: a small glycerol molecule and three small fatty acid molecules. A fatty acid is a long chain of carbon and hydrogen atoms that has a cluster of carbon, oxygen, and hydrogen at one end. Fats are triglycerides that are solid at room temperature, while oils are triglycerides that are liquid at room temperature. How do fats and oils store more chemical energy than equivalent volumes of carbohydrates? For a given volume, fats and oils contain more energy-rich carbon-hydrogen bonds than carbohydrates. The breakdown of fats and oils produces more energy in the form of adenosine triphosphate (ATP) than the breakdown of glucose. However, the first thing that happens is that the body converts these fats to glucose. A fatty acid is a long chain of carbon and hydrogen atoms.

Fats

Fats may be the premier energy-storage molecules, but your body has to expend twice as much energy to burn off a pound of fat than a pound of glycogen.

2.18 Nucleic Acids Nucleic acids are macromolecules that store and implement genetic information.

From the tallest redwood to the smallest bit of plankton in the ocean, all living things contain organic macromolecules called nucleic acids, which provide all of the instructions for an organism's growth and development. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are nucleic acids. DNA contains an organism's genetic information, which is passed from generation to generation, while RNA uses the instructions provided in DNA to build proteins. You will learn many more details about how nucleic acids store and translate information in another lesson; in this lesson, you will become acquainted with the structure of those molecules and the differences between them.

Chlorophyll is an important organic compound that contains magnesium.

Have you ever been to the tropics? What did you see there? Lush plant life? Thick, dense greenery? Leaves of all shapes and sizes? As you know, the sun is an energy source for plants. Photosynthesis is occurring in every inch of greenery on the planet. Within the cells of a plant's leaves are molecules of chlorophyll. Chlorophyll molecules capture the sun's energy, and are key in transferring that energy into chemical energy. Chlorophyll is an organic compound. Every molecule of chlorophyll has one atom of magnesium (Mg) at its center.

Steroid hormones are chemical messengers. Stress: A study of stress responses in rats shows that if rats can't turn off their cortisol stress response, they develop some of the same problems of stressed-out people: ulcers and greater susceptibility to disease.

Have you ever gone through a stressful time—you had a lot of exams and papers due in one week, or your basketball team was in the state tournament—only to come down with a cold when it was all over? It's not a coincidence. Your body produces a steroid hormone called cortisol in response to stress. One of its effects is to inhibit your immune system, making you more likely to get sick when you're stressed out. Like other hormones, cortisol is a chemical messenger. It carries information from one part of the body to another. Testosterone and estrogen, which direct your body's development into adulthood, are also steroid hormones. They are produced in the reproductive organs and travel throughout the body.

2.05 Ions in Living Things Ions are often electrical signals of cellular communication. Ions and Your Heart: In an average lifetime, a human heart beats more than 2.5 billion times. A doctor can use the electrical impulses in your body to gauge the health of your heart. The doctor attaches wires to your body that are linked to a machine called an electrocardiograph. Electrical charges travel along the wires, and the electrocardiograph translates the impulses as an electrocardiogram, a report that reflects the condition of your heart.

Have you ever gotten a small shock from static electricity? That phenomenon is possible because the surface of your body carries electrical charges. Electrical charges are also distributed inside your body in various ways. You may recall that an ion is an atom with a positive or a negative electrical charge. Ions are present throughout your body, and they are distributed in different ways. The electrical charges of ions keep your heart beating and facilitate the transfer of messages throughout your body at super-high speeds. The stability of the electrical charges and the way they are distributed are key components of any living thing. The electrical charges of ions in your body keep your heart beating and facilitate the transfer of messages throughout your body.

Animals store glucose in the complex carbohydrate glycogen.

Have you ever heard of athletes who carbohydrate load by eating a lot of pasta before a race? By eating a lot of carbohydrates, they are forcing their bodies to store extra glucose in their muscles, so it's available for them during long-endurance sports. While plants store extra glucose as starch, animals—including humans—store glucose in a molecule called glycogen. Like starch, glycogen is made up of many glucose molecules bonded together. Glycogen differs from starch in being a more highly branched molecule. Humans and other animals store glycogen mainly in muscle cells and liver cells. Like starch, glycogen is easily broken down into individual glucose molecules during times of energy demand. Those glucose molecules can then be further broken down, so their stored energy can be converted into usable forms.

Some enzymes need other molecules to work properly.

Have you ever wondered why you need to have certain vitamins in your diet? Among the many roles that vitamins play in your body is their role in helping enzymes function. Inside the body, vitamins help produce small molecules called coenzymes, which some enzymes require to function properly. Coenzymes are not permanent parts of enzymes. Instead, they move about and temporarily bind with an enzyme, then move on and interact with other enzymes. Certain enzymes also require other compounds, such as the minerals zinc (Zn) and copper (Cu). Those compounds are called cofactors. Coenzymes and cofactors may help enzymes by performing functions such as moving electrons, providing energy, or binding other molecules.

Your body uses calcium in several ways.

Have you noticed phrases like "a good source of calcium" plastered on the containers of many foods and drinks? You probably associate calcium with dairy products, but many other products—juices, for example—are fortified with calcium. Getting enough calcium in your diet is important. Calcium (Ca) plays an important role in the development of bones and teeth. This is especially important for young people who are still growing. Calcium is also critical to the function of muscles, the clotting of blood after an injury, the transfer of nerve messages around your body, and the regularity of your heartbeat. One of calcium's most important roles is to help regulate the substances that cross cell membranes. In your body, calcium exists as the ion Ca2+.

Potassium ions help regulate the heartbeat.

Hold your arms out like a bird and flap them up and down. Don't worry, no one can see you! Now flap them as fast as you can. How many times could you flap your arms in a minute? 60? 75? The ruby-throated hummingbird can flap its wings approximately 65 times per second. A workout of that magnitude requires a lot of cooperation from the heart. A hummingbird's heart beats approximately 1,200 times per minute when the bird is feeding. Potassium ions (K+) are critical components in that task. They play a key role in how materials move into and out of cells—including heart muscle cells. In addition, potassium ions keep other muscles working properly and act as messengers between muscles and nerves. Potassium ions are also important in keeping blood pressure regulated. Potassium ions help a hummingbird's heart and muscles work properly.

Elements are made of atoms.

If you could take any element—carbon, for example—and divide it again and again until you found its smallest part, what would that smallest part be? An atom Opens in modal popup window . Atoms are the basic unit of matter. Atoms are so small that no one can see them, not even with a microscope. Scientists have discovered details about atoms by doing experiments that show how atoms act under certain conditions.

Some bacteria and fungi can digest cellulose. Making Ethanol from Cellulose Scientists and engineers are trying to find new ways to make the renewable fuel ethanol from cellulose. They are investigating the use of the types of bacteria that live in termite guts and elsewhere to help break down cellulose into sugars that can be turned into ethanol.

If you've ever seen decaying logs on the forest floor, then you've seen one type of organism that can digest cellulose: fungi. Some species of fungi produce enzymes that break down cellulose. These fungi play an important role in recycling dead trees and other plants in the forest. Termites—insect pests that can damage homes and other structures by feeding on wood—have bacteria in their guts that break down cellulose. By themselves, termites cannot digest the cellulose in wood, but the bacteria in their stomachs produce cellulose-digesting enzymes. Without those bacteria, the termites would not be able to digest wood and get energy and nutrients from it. Animals like cows also are home to many types of cellulose-busting bacteria, which live in their stomachs.

Hemoglobin is an organic compound that contains iron.

Imagine being on a cruise in the North Pacific. While scanning the horizon, you spot something in the distance—an enormous whale. The whale breaches, captivating everyone on the ship as it throws its massive body out of the water. Then it exhales, spouting a tall plume into the air. When the whale inhales again, its body must deliver oxygen evenly to its trillions of cells without stopping. To power this process of delivering oxygen to cells, a unique organic compound called hemoglobin captures the oxygen from the whale's lungs and delivers it to the rest of the body. The critical atom in hemoglobin is iron (Fe).

Penicillin fights bacterial infections. It comes from a fungus.

In 1928 a Scottish scientist named Alexander Fleming decided to take a short vacation. Before he left, he started to grow some bacteria that he planned to study when he got back. Downstairs from Fleming's lab, a group of scientist were studying fungi. While Fleming was away, some spores of a fungus called Penicillium notatum got loose from the lab downstairs and floated upstairs, where they fell into Fleming's bacteria culture. When Fleming returned from his vacation, he looked at his bacteria culture. In the area where the fungus spores had landed, the bacteria had stopped growing completely. Surprised, Fleming performed a series of experiments that proved the fungus had the ability to kill certain kinds of harmful bacteria. Fleming had discovered the source for a medicine that has since saved millions of lives—penicillin. A fungus called Penicillium notatum is the source for the powerful antibiotic penicillin.

Quinine is a medication used to treat malaria and is made from a plant compound.

In a busy marketplace in Algiers, a female mosquito lands on a man selling fresh dates and drives her proboscis into his skin. When she flies off, she leaves with more than just a full stomach. She also carries some of the malaria parasites that were present in the man's blood. When the mosquito bites a young boy, some of the parasites are deposited into the boy's bloodstream. About a week later, the boy falls ill as the malaria plasmodium begins to destroy his red blood cells. Luckily for the boy, he has access to quinine, a medicine that comes from the bark of the cinchonatree. French scientists isolated quinine (C20H24N2O2) from the tree bark in 1820. Quinine is effective in treating the symptoms of malaria.

Enzymes bring molecules together.

In addition to binding specific molecules, enzymes also hold molecules in specific orientations, allowing two molecules to form a chemical bond that would not normally form. Inside a cell, substrate molecules—such as individual amino acids—may move about freely, like particles suspended in water. Even if two molecules that could form a bond bump into each other, if the correct parts of the molecule don't come into contact with one another, then no bonding takes place. Enzymes help ensure that the correct regions of molecules interact with each other. In protein synthesis, for example, the amino end of one amino acid forms a peptide bond with the carboxyl end of another. An enzyme that can hold both substrates together in the proper orientation helps ensure that peptide bonds can form between amino acids.

Reserpine, a medication for high blood pressure, comes from a plant.

In the 1930s, scientists began studying Rauwolfia serpentina, Indian snakeroot, which villagers in India had used for centuries as a treatment for epilepsy, insomnia, and mental disorders. The scientists found that certain chemicals in the plant dramatically reduced blood pressure. The active compound that they isolated from the plant is called reserpine (C33H40N2O9). Reserpine binds to the parts of nerve cells that contain important chemical messengers and has a suppressing effect on them. When the chemical messengers are blocked, the blood vessels dilate, and blood pressure goes down. Indian snakeroot (Rauwolfia serpentina) contains reserpine, which lowers blood pressure.

One type of plant produces glycogen.

In the forests of Costa Rica lives a cecropia tree, which is unique among all the plants on earth: It produces glycogen, the glucose storage molecule normally found in animals. How do scientists explain this puzzle? Cecropia trees are almost always colonized by stinging ants, which protect the trees from intruding animals that might otherwise eat the trees' leaves. What do the ants get for their role in guarding the trees? A glycogen meal. It turns out that the ants living on cecropia trees feed on bundles of glycogen called Müllerian bodies, which the tree produces. Ecologists believe that, over time, cecropia trees evolved this mechanism, which feeds the ants a form of carbohydrate that plants don't normally make. This mechanism provides the ants with a ready-to-use form of chemical energy. And, because the ants don't need to look for food elsewhere, it guarantees that the trees will always have their sentries on hand.

The nitrogenous bases in DNA pair up in a very specific manner.

Inside DNA's double helix are nitrogenous bases. Look closely at the structure on the right. Do you notice any pattern to the structure? Which bases pair up with one another? Not only are the nitrogenous bases located inside the double helix, but also they align with each other in a specific way. In a DNA molecule, adenine and thymine bases always pair up, and cytosine and guanine always form a pair. This pattern of matching is called complementary base pairing. Complementary base pairing can be summarized by the base-pairing rules that adenine (A) and thymine (T) always pair up, and cytosine (C) and guanine (G) always pair up.

The primary structure of a protein is its sequence of amino acids.

Inside each of your red blood cells are molecules of a protein called hemoglobin, which binds with oxygen in your lungs and carries it to all of your body's parts. In most people, red blood cells are shaped like a squashed bread roll—roughly spherical but indented in the center. Individuals with the inherited disorder called sickle-cell anemia, however, have red blood cells with an altered shape. That shape interferes with the cells' ability to travel through the smallest blood vessels (the capillaries). A change in just one amino acid in one polypeptide chain in the hemoglobin molecule causes this painful disorder. At the molecular level, scientists would say a change in the primary structure of hemoglobin accounts for the disease. The primary structure of a protein is its sequence of amino acids. As this example shows you, the primary structure plays an important role in protein function. The red blood cell on the left has been altered by a change in the primary structure of the protein hemoglobin.

Insulin

Insulin is the protein that helps the body regulate the level of sugar in the blood. Diabetes develops when the body either does not produce enough insulin, or does not respond to the insulin present in the bloodstream.

Complex Carbohydrates

It takes your body longer to digest complex carbohydrates, such as whole fruits, vegetables, and whole grains, than it does to digest simple carbohydrates like sugar. That's part of the reason why you'll feel full for much longer after eating a bowl of oatmeal than after eating a bowl of sugary cereal.

Enzymes themselves are not permanently changed in the course of a reaction.

Lactase is the enzyme that interacts with the molecule lactose. That interaction breaks the bond holding together the two monosaccharides, galactose and glucose, that make up a lactose molecule. The structure and function of the lactase enzyme remain unchanged during the course of the reaction. After the bond is broken, the lactase enzyme is free to catalyze more reactions with other lactose molecules. This is an important aspect of enzyme biology: Enzymes help speed up chemical reactions, but they do not themselves change as a result of the reaction. Enzymes are essentially recycled in the course of a reaction. For this reason, chemical reactions often require only a small concentration of enzymes.

Ionic bonds form between positively and negatively charged atoms.

Let's check out one kind of bond—an ionic bond Opens in modal popup window . Have you ever played with magnets? If so, then you know that the opposite poles of magnets (the positive and negative poles) attract each other. Like the poles of a magnet, positively charged atoms and the negatively charged atoms attract. An atom with an electrical charge is called an ion, so when two ions bond, they form an ionic bond. A good example of an ionic bond is found in a sodium chloride molecule. The positively charged sodium (Na) atom gives up a valence electron to the negatively charged chlorine (Cl) atom. The compound that these two atoms create is quite different from the two original elements. You know it as common table salt (NaCl). Explore the process of an ionic bond forming between sodium and chlorine atoms.

Carbon dioxide dissolves into bicarbonate ions.

Let's take a trip to the plains of Africa, where a cheetah is in hot pursuit of a Thomson's gazelle. The cheetah's claws dig into the earth as the big cat pursues the gazelle at 113 km (70 mi) an hour. The gazelle darts back and forth to evade the speedy cheetah. Both animals are breathing heavily. Large amounts of carbon dioxide (CO2) are being generated in the two animals' bodies, much of which is breathed out as carbon dioxide gas. Some of the carbon dioxide in their blood is converted into bicarbonate ions (HCO32-). This conversion must happen to keep the acid balance of their body fluids at a level that allows the cells to function properly. Bicarbonate ions serve as buffers that keep the acids at levels that cells can tolerate. Large amounts of carbon dioxide in the blood are converted to bicarbonate ions to maintain a proper acid balance in an organism's cells.

2.06 Useful Chemicals from Living Things Different cultures have used natural compounds for health purposes for thousands of years.

Let's visit eastern North America in the year 1500. A Cherokee infant has a high fever. His parents and grandparents huddle near him, wiping his tiny forehead with a damp cloth. They send for the medicine man, who administers a drink that contains the crushed leaves of a local willow tree. Soon the boy's fever goes down, and he is able to sleep. What was in the willow mixture that reduced the baby's fever? In many Native American cultures, the medicine man treated sick tribe members with natural compounds.

An enzyme's environment influences its activity. Have a Fever? Many enzymes that are active in your body work best at the high temperatures found inside the human body. Enzymes in some of the bacteria that cause infection, however, don't function as well at high temperatures. When you develop a fever, you body temperature may rise to a point that's hot enough to disrupt, or denature, some of the proteins essential for bacteria to survive.

Like all proteins, enzymes are sensitive to changes in their environment, such as temperature, pH, and ionic conditions. And each enzyme has a specific set of conditions that are ideal for its activity. Changing those conditions may affect an enzyme's activity or stop it altogether. As you learned earlier, high temperatures may denature, or break down, a protein like an enzyme, changing its overall shape and, therefore, its ability to function. The pH of an enzyme's environment—how acidic or basic the environment is—also affects an enzyme's activity. The enzyme pepsin, for example, digests proteins in the stomach, where the pH is extremely acidic. The enzyme salivary amylase, which digests starches in the mouth, functions at a much less acidic pH.

Carbon is present in lipids.

Lipid is another word for fat. You may have a negative association with the word fat, but without fats you couldn't function. Every cell in your body is surrounded by a membrane made mostly of fats. Your nerves are insulated with fats. Your body stores extra energy in the form of fat. A basic unit of many lipids is the molecule glycerol, which contains a chain of carbon atoms. Carbon's unique bonding ability makes it ideal for bonding with other carbon atoms.

Lipids store energy, form cellular membranes, and transmit chemical messages.

Lipids are organic molecules made largely of carbon and hydrogen. Most lipids contain long chains of carbon and hydrogen atoms linked together in various ways. Lipids repel water, are ideal molecules for energy storage, transmit chemical messages, and provide waterproof coatings for many organisms. The main classes of these organic molecules are fats, oils, phospholipids, steroids, and waxes.

Cellulose gives plants strength and support. All plants on earth produce an estimated 100 billion tons of cellulose every year, making it the most abundant organic compound on earth.

Looming overhead at more than 100 m tall, the coastal redwood is the tallest living thing on earth. What gives that tree the strength to support its leaves and branches at such great heights? The same molecule that makes up the rugged cell walls characteristic of all plants: cellulose. Like starch, cellulose is a complex carbohydrate made up of many molecules of glucose linked together. But unlike starch, plants do not use cellulose to store energy. Instead, plants use cellulose as a structural molecule. It forms the cell wall that gives plant cells shape and support. The glucose molecules in cellulose are held together with a different type of chemical bond than the glucose molecules in starch. This bond is much more difficult to break down, making cellulose an ideal structural molecule.

Proteins perform many functions.

Many cooks use meat tenderizer, a powder that, when applied to a cut of meat, improves its taste and softens the texture. How does it work? Most meat tenderizers contain an enzyme, a type of protein extracted from papaya. The enzyme papain breaks peptide bonds. Because meats are largely composed of protein, breaking down those peptide bonds helps soften their texture. Enzymes are just one type of protein found in living organisms. Proteins also provide support, structure, and storage; help organisms maintain homeostasis; defend organisms from disease; and help carry important molecules throughout the body. Dogs have enzymes in their saliva that help break down food. These enzymes perform the same function as the enzymes in meat tenderizers.

Carbon is present in proteins.

Many structures in your body are made of or contain proteins, and proteins are made of molecules called amino acids. Amino acids are present in muscle tissue, hair, blood, digestive enzymes, and many other parts of your body. Alanine is one example of an amino acid. Carbon atoms are at the center of all amino acids.

Several types of ions are critical to living things.

Many types of chemical compounds are necessary for living things. Carbohydrates, protein, and fats are important, and so is oxygen gas and carbon dioxide gas. Equally important are certain kind of ionic compounds and the ions they release when dissolved in water. The power of these ions comes from the fact that they are electrically charged. Their electrical charge allows them to play critical roles in the body. Ions like Na+, Ca2+, K+, and Cl- play key roles in the body, including helping regulate what gets into and out of cells, and keeping acids and bases balanced in the body.

Ions play critical roles in living things.

Many types of ions are extremely important to the survival of living things. For example, when you eat food with salt, the chemical compound sodium chloride (NaCl) dissolves in your body fluids into sodium ions (Na+) and chloride ions (Cl-). When you ingest sodium chloride, you are ingesting an inorganic compound —it does not contain carbon. You are also ingesting an ionic compound. When table salt dissolves in water, or in your mouth and stomach, its atoms separate into the ions Na+ and Cl-. These ions, each with an electrical charge, now become active in your body in different ways. In your body, salt (NaCl) breaks up into sodium ions (Na+) and chloride ions (Cl-).

Matter

Matter consists of elements which are made of similar atoms which are made of protons, neutrons, and electrons.

Matter on earth exists most often in the form of elements.

Matter exists in many different forms. One of the most fundamental kinds of matter is an element Opens in modal popup window . An element is, as you will soon see, a substance that is made of only one kind of atom. You may be familiar with some elements, such as silver, copper, and carbon. Every element has its own characteristics and properties. An element's properties determine how the element interacts with everything around it.

In some chemical systems, a hydrogen bond will form between molecules.

Now think about what would happen if two unevenly charged water molecules came near each other. How would they react? A slightly negative oxygen atom (O) would attract a slightly positive hydrogen atom (H). A hydrogen bond Opens in modal popup window is an electrical attraction between partially charged molecules that contain hydrogen atoms. Hydrogen bonds are pretty weak compared to the other two kinds of bonds. Turn to pages 22- 23 of your reference book to review ionic, covalent, and hydrogen bonds.

Nucleic acids are organic macromolecules that store and transmit genetic information and play a central role in building proteins.

Nucleic acids are large, carbon-containing molecules called DNA and RNA. Each of these molecules is made up of five-carbon sugars, phosphate groups, and nitrogenous bases. DNA exists as a double-stranded molecule, often called a double helix for its twisted-ladder shape. RNA exists as a single-stranded molecule. The information in DNA is encoded in the precise sequence of nitrogenous bases in its structure. RNA uses the sequence of those bases as a template for the assembly of proteins. The information in DNA is passed from generation to generation.

Nucleic acids are made of repeating units of five-carbon sugars, phosphate groups, and nitrogenous bases.

Nucleic acids are made of smaller units called nucleotides, which are molecules that share a general chemical structure. A nucleotide Opens in modal popup window is a small molecule made of five-carbon sugars, a phosphate group, and a nitrogenous Opens in modal popup window base. As you can see on the right, a phosphate group contains atoms of phosphorous (P) and oxygen (O). And as the name suggests, a nitrogenous base is a structure containing nitrogen (N). Both DNA and RNA are formed when the sugar of one nucleotide bonds with the phosphate group of another nucleotide. Multiple nucleotides bond together in this way, forming what some scientists call a sugar-phosphate backbone.

A few elements are found in pure form on earth.

Of the approximately 115 known elements, 92 occur naturally on earth. Of these, however, very few exist in pure form. In fact, most elements in nature are bound up with other elements in complex chemical compounds. Two of the most important elements used by humans are iron and copper. The discovery of those two elements had an enormous impact on society. Most notably, people began using iron and copper instead of stone to make tools and weapons. The discovery of iron and copper changed society as people learned to make tools from those elements.

Easing the Pain

Papain also helps break down the protein-based toxins in jellyfish and bee venom. When stung, people sometimes make a paste of meat tenderizer and water, and then they apply it to the painful area.

Cohesion and adhesion play a role in the movement of water in plants.

Picture yourself strolling through a forest of tall, majestic trees. You approach one massive specimen and look up. The branches are so high you can hardly see the leaves. You wonder how water ever gets all the way up there from the roots. Within the trunks of trees and the stems of plants are narrow, tubelike structures that serve as conduits for carrying water and nutrients from the roots to the rest of the plant. Because of water's adhesive properties, water molecules inside the tubes are attracted to the tubes' inner surface. Because of water's cohesive properties, the rest of the water molecules are pulled along with them. Thus, cohesion and adhesion play a role in the movement of water from the roots to the leaves. Turn to page 43 in your reference book to read more about cohesion, adhesion, and surface tension.

Enzymes allow bonds to form

Positioned at the top of the space is the title, Enzymes Allow Bonds to Form. Positioned in the middle of the space is a dark irregular shape labeled, enzyme. The shape is generally oblong. It has one smooth side. The opposite side has a long very jagged area. Positioned at the top right of the space are two smaller shapes, labeled substrate molecules. Positioned at the bottom of the space is the caption: In addition to breaking down complete molecules, enzymes can help substrates bind into new molecules. The two smaller shapes move down and toward the jagged area of the enzyme. The shapes continue to move until they reach the jagged area, where they fit together and bond to the enzyme. The shapes combine to form a single shape labeled, enzyme-substrate complex. Positioned at the bottom of the space is the caption: The substrates precisely fit an enzyme's active site. The enzyme-substrate complex, now joined to form one molecule, moves up and away from the enzyme. When that happens, the molecule is labeled, new product molecule. Positioned at the bottom of the space is the caption: A reaction occurs; the two substrates emerge as a new product.

Enzymes and Bonding

Positioned at the top of the space is the title, Enzymes Allow Bonds to Form. Positioned in the middle of the space is a dark irregular shape labeled, enzyme. The shape is generally oblong. It has one smooth side. The opposite side has a long very jagged area. Positioned at the top right of the space are two smaller shapes, labeled substrate molecules. Positioned at the bottom of the space is the caption: In addition to breaking down complete molecules, enzymes can help substrates bind into new molecules. The two smaller shapes move down and toward the jagged area of the enzyme. The shapes continue to move until they reach the jagged area, where they fit together and bond to the enzyme. The shapes combine to form a single shape labeled, enzyme-substrate complex. Positioned at the bottom of the space is the caption: The substrates precisely fit an enzyme's active site. The enzyme-substrate complex, now joined to form one molecule, moves up and away from the enzyme. When that happens, the molecule is labeled, new product molecule. Positioned at the bottom of the space is the caption: A reaction occurs; the two substrates emerge as a new product.

ATP and Energy

Positioned in the center of the space is a large, irregular dark shape. The shape is labeled, enzyme. A label points to the bottom side of the shape. The label is, active site. Under the large shape and to the left are two identical small, light hexagons next to each other. Positioned below these hexagons is a third identical hexagon. A label points to the hexagons. The label is A T P, in parentheses adenosine triphosphate. Positioned on the right side of his hexagon is a chain of three balls. Each ball contains the letter P. Presumably, P stands for phosphate. A dark thick line connects the third hexagon to the leftmost ball. Similarly, a dark thick line connects the leftmost ball to the middle ball. A lighter thick line connects the middle ball to the rightmost ball. Under the large shape and to the right are two smaller medium-light irregular shapes. A label points to these shapes. The label is, substrates. The labels disappear and the A T P and the substrate shapes move toward the large dark shape. The A T P bonds on the left side of the lower part of the large shape. The substrates fit together with each other and bond on the right side of the lower part of the large shape. When this happens the space between the A T P and the substrates is illuminated with several flashes. When the flashes stop, the A T P and the substrates move down and away from the enzyme. The substrates are now one shape with a thick line in the middle. Then the rightmost phosphate attached to the chain that is connected to the hexagon separates from the chain and moves down and to the right. The enzyme at the top of the space is now labeled, unchanged enzyme. The substrate is now labeled, new product. The A T P is now labeled A D P, in parentheses adenosine diphosphate. The ball that separated from the chain of balls is labeled, free phosphate. A caption at the bottom of the space: A T P contains a high-energy bond that gives immediate energy where it's needed. As this bond breaks during a chemical reaction, the energy that was in the bond is used to drive other chemical changes.

Peptide Bonds

Positioned in the center of the space is a very dark circle labeled, amino acid. Another circle of the same size moves in from the upper left of the space and stops just above the first circle. This circle is dark, but not very dark. A vertical line joins the two circles. The line is labeled, peptide bond. A third circle of the same size moves in from the lower right of the space and stops just below the first circle slightly to the right. This circle is medium dark. As before, a line joins the third circle to the first circle. The three amino acids form a kind of chain, Then, a series of amino acids move in from the right and left and join the chain at the top and at the bottom. At the end of the presentation there are nine amino acids in the chain. They range from very dark, to medium dark, to light. Presumably, each shade represents a different amino acid.

Coenzymes

Positioned in the middle of the space is a dark irregular shape labeled, enzyme. The shape is generally oblong. It has one rather smooth side. The opposite side is long and very irregular. A label pointing to the irregular side of the enzyme is, active site. Positioned at the top right of the space is a light shape, labeled substrate. This shape is about the same size as the irregular part of the enzyme. Positioned to the left of the substrate is a small medium-dark shape. This shape is labeled, coenzyme. A caption at the bottom of the space: Some enzymes require the help of coenzymes or cofactors to perform their functions. The labels disappear and the coenzyme begins to move toward the enzyme. The coenzyme fits into a place in the irregular part of the enzyme. When that happens, the substrate moves down toward the enzyme. The substrate fits into the irregular part of the enzyme including the place where the coenzyme bonded with the enzyme. After that, the substrate changes. The right part of the substrate becomes dark. The left part of the substrate becomes medium-dark. Then, three labels appear. The label coenzyme points to the small shape that fit into the enzyme. The label enzyme-substrate complex points to the two parts of the substrate that fit into the enzyme. The third label, enzyme, points to the large irregular shape. Next, the coenzyme and the two parts of the enzyme-substrate complex move up and away from the enzyme. The coenzyme is labeled, coenzyme. The two parts of the enzyme-substrate complex are labeled, new products. The enzyme is labeled, unchanged enzyme. Positioned at the bottom of the space is the caption: Once the new products are released, the unchanged enzyme and the unchanged coenzyme are free to repeat the process.

Hydrogen Bonds

Positioned in the space are three molecules of H sub 2 O. One of the molecules is in the upper left of the space. One is positioned in the upper right. And one is positioned in the lower part of the space. Each molecule is represented as follows. Positioned in the center of the molecule is a ball with the letter O. The ball represents the nucleus of the oxygen atom. Positioned to the right of the nucleus is a ball with the letter H. Positioned to the left of the nucleus is another ball with the letter H. These are the nuclei of hydrogen atoms. Surrounding the oxygen nucleus are two concentric circles. Surrounding each hydrogen nucleus is one circle. The circles surrounding the hydrogen nuclei overlap with the outer circle of the oxygen nucleus. Positioned on the circles are small dots. The dots represent electrons. The electrons on the circles surrounding the oxygen nucleus are as follows. Positioned on the inner circle, are two electrons on opposite sides of the nucleus. Positioned on the outer circle are eight electrons as follows. Two pairs of electrons are positioned opposite the single electrons. Next to one of the pairs, just outside the circle is a negative sign. The negative sign is toward the center of the space. Positioned on the left side of the outer circle is another pair of electrons. These electrons are also on the circle surrounding the hydrogen atom. This suggests that the hydrogen atom and the oxygen atom share these electrons. Similarly, positioned on the right side of the outer circle is also a pair of electrons. These electrons are also on the circle surrounding the other hydrogen atom. Positioned near the circle surrounding each hydrogen atoms is a plus sign. The plus signs are toward the edges of the space. The molecule in the lower part of the space rotates in a clockwise direction so the negative sign faces up and to the right instead of toward the center of the space. When that happens, the molecule in the upper left moves down and to the right toward the molecule that just rotated. The negative sign in the outer circle of this molecule moves toward the circle surrounding the hydrogen atom and bonds with it. After that, the molecule in the upper right rotates clockwise so the negative sign is facing up and to the left instead of down, and one of the hydrogen atoms faces the oxygen atom of the lower molecule. When that happens, the rotation stops and the oxygen and hydrogen atoms bond. At the end of the presentation, the H sub 2 O molecule at the upper left of the space is bonded with the hydrogen atom of the H sub 2 O molecule at the bottom of the space. That H sub 2 O molecule is bonded with the hydrogen atom of the H sub 2 O molecule at the upper right of the space.

Denatured Enzyme

Positioned in the upper left of the space is the title, Denatured Enzyme. Positioned in the middle of the space is a dark irregular shape labeled, enzyme. The shape is generally oblong. It has one smooth side. The opposite side has a long very jagged area. Positioned at the top right of the space is a light shape, labeled substrate. This shape is about the same size as the jagged part of the enzyme shape. Positioned at the far left of the space is a thermometer. The thermometer has six tick marks. The tick marks are not labeled. The indicator on the thermometer suggests that the temperature is at the second tick mark from the bottom. A caption at the bottom of the space: High temperatures can alter the shape of an enzyme. The temperature indicator goes up. When this happens, the shape of the enzyme changes. For example, the enzyme gets deeper in shape and the jagged side gets a little smoother. Then the smooth side of the enzyme becomes more distorted. At the same time, the substrate moves toward the enzyme. As the temperature continues to rise, the substrate moves closer and closer until it can fit within the jagged part of the enzyme. The substrate and enzyme touch. When that happens, the substrate bounces right and left and up and down. The substrate and the enzyme do not fit together. When the temperature is between the fourth and fifth tick marks, the substrate begins to move away from the enzyme. When the substrate reaches its original position, movement stops. The enzyme is now labeled, denatured enzyme. Positioned at the bottom of the space is a caption: Alterations in the shape of the enzyme may prevent it from binding with the substrate.

Enzyme-Substrate Complex

Positioned in the upper left of the space is the title, Enzyme-Substrate Complex. Positioned in the middle of the space is a dark irregular shape labeled, enzyme, in parentheses lactase. The shape is generally oblong. It has one smooth side. The opposite side has a long very jagged area. The jagged edge is labeled, active site. Positioned at the top right of the space is a light shape, labeled substrate, in parentheses lactose. This shape is about the same size as the jagged part of the enzyme shape. A caption at the bottom of the space: The substrate precisely fits an enzyme's active site. The labels disappear and the substrate begins to move toward the enzyme. The substrate fits into the jagged part of the enzyme. When that happens, the label, enzyme-substrate complex, appears. Then, the substrate divides into two parts. When that happens, the enzyme is labeled, lactase. The two parts of the lactose substrate are labeled, products. The part on the left is labeled, galactose. The part on the right is labeled, glucose. Then, a caption appears. The caption: A reaction occurs; lactose is broken into its component sugars Next, the products move out and away from the lactase enzyme. The enzyme does not move or change. The labels galactose, glucose, and lactase appear again. Positioned at the bottom of the space is the caption: The products detach. The enzyme remains unchanged.

How Lactase Works

Positioned in the upper left of the space is the title, How Lactase Works. Positioned in the middle of the space is a dark irregular shape labeled, lactase. The shape is generally oblong. It has one smooth side. The opposite side has a long very jagged area. Positioned at the top right of the space is a light shape, labeled lactose. This shape is about the same size as the jagged part of the lactase shape. A caption at the bottom of the space: Lactase and lactose fit together precisely. The labels disappear and the lactose begins to move toward the lactase. The lactose fits into the jagged part of the lactase. Then, the lactose divides into two parts. One part is dark. One part is light. The dark part on the left is labeled, galactose. The light part on the right is labeled, glucose. Then, a caption appears: A reaction occurs; lactose is broken into its component sugars. Next, the galactose and glucose move out and away from the lactase. The enzyme does not move or change. After the galactose and glucose stop moving, the labels, galactose, glucose, and lactase appear again. Positioned at the bottom of the space is the caption: The products detach. The enzyme remains unchanged.

Animals can break down starch for energy.

Potatoes, rice, corn, and many other foods you eat contain high levels of starch, which is stored by plants. Fortunately, your body can break down those starch molecules to release the glucose molecules you rely on for energy. Like most other animals' bodies, your body produces enzyme Opens in modal popup window molecules. Specific enzymes in your body—especially one called amylase—break the type of chemical bond that links glucose molecules together in starch molecules. When glucose is released from starch molecules, it is free to enter the chemical reactions that transform the chemical energy in a glucose molecule into forms of energy your body can use for growth, development, and maintenance.

Proteins are organic molecules that play numerous important roles in the body, including storage, transport, response, and defense.

Proteins are large organic molecules made of one or more polypeptides, which are chains of amino acids linked by peptide bonds. Proteins play many important roles in living organisms, including storage, transport, response, and defense.

RNA is a single-stranded nucleic acid.

RNA is similar to DNA, but there are several important differences. The sugar-phosphate backbone of RNA is made up of the sugar ribose. In addition, RNA uses a nitrogenous base called uracil in place of thymine. Like thymine, uracil Opens in modal popup window is complementary to adenine. And finally, RNA exists most of the time as a single-stranded molecule inside of a cell. While DNA contains the genetic instructions for making proteins in the sequence of its nucleic acids, RNA helps cells read those instructions in DNA and use them to make proteins.

Cells contain different types of RNA molecules.

RNA plays several important roles in translating the information contained in DNA into amino acids, which are the building blocks of protein. Cells have three different types of RNA: mRNA, or messenger RNA rRNA, or ribosomal RNA tRNA, or transfer RNA Each type of RNA is produced during a process called transcription. RNA plays the role of intermediary between the information in a strand of DNA and the protein produced from that information.

Amino acids combine to form peptides.

Regardless of the R-groups that they contain, amino acids bond with one another in the same way, forming a structure called a peptide. A peptide consists of two or more amino acids. A peptide bond forms when an enzyme—a type of protein that speeds up chemical reactions—causes a dehydration reaction. In this reaction, the-OH end of the carboxyl group joins with the hydrogen atom (H) from the amino group. This reaction produces a molecule of water and a peptide bond between the two amino acids. This type of reaction can repeat many times to form a polypeptide, or a long chain of linked amino acids.

Hydrogen bonds form between the nitrogenous bases in a DNA molecule.

Remember how the nitrogenous bases adenine and guanine consist of two rings of carbon and nitrogen, while cytosine and thymine each contain only one? Inside the double helix, a double-ring structure always pairs with a single-ring structure, which helps stabilize the helical structure. Hydrogen bonds form between the nitrogenous bases inside a DNA molecule—two bonds between adenine (A) and thymine (T) and three bonds between cytosine (C) and guanine (G). Those bonds give additional support to the molecule. You may think of the bonds between the bases in a DNA molecule as the rungs of the ladder whose outer rails are formed by the sugar-phosphate backbone.

Saturated fats have single bonds between carbon atoms.

Saturated and unsaturated fats have been getting a lot of attention in the news for their roles in health and nutrition. You may have heard that unsaturated fats are healthier for you than saturated fats are. The structure of each of those categories of fat explains why and tells you some important things about lipid structure. First look at saturated fats. Many of those fats are found in animals and the animal food you eat. A carbon atom has space to form four chemical bonds with other atoms. A saturated fat is made up of fatty acid chains with single bonds between each carbon atom. In the chain, two bond spaces are taken up by other carbon atoms. The other two bond spaces are filled with hydrogen atoms. Because all remaining spaces are filled with hydrogen atoms, the fat is said to be saturated. That arrangement makes long, straight fatty acid chains, which can easily pack together. Scientists suggest that the ability to pack together may cause saturated fats to build up in the arteries, possibly leading to heart disease.

Many natural compounds are used to fight cancer.

Scientists are working feverishly to develop cancer-fighting drugs, and they've developed several from natural compounds. One example is Taxol, which comes from the Pacific yew, Taxus brevifolia. Taxol is a large organic molecule whose chemical formula is C47H51NO14 . Taxol helps stop the spread of cancer. Cell division is a natural process, but in cancerous cells it runs rampant. Taxol inhibits the reproduction of cancer cells, helping block the growth of new cancer cells. Another compound called ellagic acid, found in strawberries, raspberries, grapes, and walnuts, inhibits the growth of cancer cells. That compound and many other natural compounds are being studied as potential cancer fighters.

2.04 Organic Compounds and Trace Elements Over time, scientists learn more about organic compounds.

Scientists first used the term organic compound in the nineteenth century to describe any substance made by living organisms. They thought that only living things could make those compounds. Then, in 1828, German chemist Friedrich Wöhler synthesized urea—a substance found in the urine of animals. That development disproved the earlier belief, showing how science changes when new evidence becomes available. Now, scientists define organic compounds as those that contain carbon bonded to at least one other type of atom, usually hydrogen. More than 8 million organic compounds exist, and many more are made each year as scientists synthesize new ones. Organic compounds in industrial products—such as rubber, plastics, fuels, pharmaceuticals, cosmetics, detergents, dyestuffs, and agrichemicals—are central to international economic growth.

Enzymes are necessary for maintaining most of the characteristics of life. Other Enzymes Amylases: break up starches Cellulases: Break up cellulose fibers. Remover tiny fibers from cotton cloth that make the cloth stiff and clothes dull. Lipases: break up oils and fats Proteases: Break up proteins

Scientists have identified more than 1,500 different enzymes Opens in modal popup window in the human body that play specific roles in many of the processes necessary for life. Many more enzymes exist in other kinds of living things. Scientists use the suffix -ase to indicate that a chemical is an enzyme. You've seen that lactase helps break down the complex sugar lactose into two simpler, more digestible sugars. Lactase, with the -ase ending, acts on lactose, a sugar. Scientists also group enzymes based on common activities they share. You can see some of the enzyme groups in the table on this screen.

There are many types of elements, some of which are important to living things.

Scientists have organized all known elements in the universe into a table called the Periodic Table of the Elements. Click Periodic Table, and click each box for a closer look at each element. When those elements interact, they form the chemical compounds of life. Only four elements make up more than 96 percent of the mass of all living things: hydrogen, carbon, oxygen, and nitrogen. In particular, carbon plays a central role. The letter symbols for each element represent a single atom of that element. For example, a single atom of carbon is represented by the letter C. A single atom of oxygen is represented by the letter O. Explore some of the elements in the Periodic Table. You may also turn to pages 18-19 in your reference book to review the Periodic Table. Periodic Table Opens in modal popup window

Hydrogenation

Shortening, which is a solid form of vegetable oil, is formed by hydrogenation, a process that adds hydrogen atoms to the double-bonded carbon in an unsaturated fat. That process smooths out the kinks in the molecule, allowing it to form a solid. Solidified vegetable oils are also called trans fats, which are less healthy than their liquid counterparts.

Changes in primary structure affect protein function.

Sickle-cell anemia is most commonly caused by a substitution of the amino acid valine for the amino acid glutamic acid. Normal hemoglobin protein has a molecule of glutamic acid at the sixth position in one of its polypeptide chains; the sickle-cell form has valine in its place. How can such a simple change in a protein that contains hundreds of amino acids cause such havoc with human health? Recall what you learned previously about amino acids. These molecules contain units called R-groups, or side chains. Glutamic acid is a charged amino acid that is hydrophilic (water loving). Valine, however, is nonpolar and hydrophobic (water avoiding). The hydrophobic valine of one chain is attracted to the hydrophobic valine in other chains within a red blood cell. This attraction causes the protein to twist in unnatural ways, causing the whole cell to take on a sickled or puckered shape. Explore the difference between normal and mutated hemoglobin.

2.15 Amino Acids and Proteins Amino acids are important chemical building blocks.

Silk may be one of the finest materials for formalwear like wedding or prom dresses, but did you know that silk comes from the salivary glands of a moth larva? The larva, or caterpillar, of a silkworm moth builds a cocoon out of protein, a type of organic molecule, which is secreted in its saliva. Silk makers harvest these cocoons and spin the protein threads into fabric. Silk protein is made up of molecules called amino acids. Amino acids are the chemical building blocks of all proteins, which are large molecules with many important functions. In this lesson, you will learn about the structure of amino acids and proteins and their importance to living things. Silkworm cocoons and worms on leaves The larvae of silkworm moths build cocoons from protein, a type of organic molecule.

DNA is shaped like a twisted ladder or double helix.

Start exploring nucleic acids by looking at the geometric shape of DNA. In 1953, after years of research, American scientist James Watson and English scientist Francis Crick were able to determine that DNA was arranged in a shape called a double helix. What is a double helix? Imagine a ladder. Now twist each end of the ladder in a different direction—that's a double helix. Here's another picture to imagine. You know what a Slinky® toy is, right? A Slinky is a helix. It spirals round and round. Now imagine two Slinkys running parallel to each other, making a double helix. You will soon see that one kind of RNA is shaped as a single helix—so you can say that it is shaped like one Slinky.

Water surface tension is a result of cohesion.

Tadpoles wiggle around in the leaves and debris of a pond. Above them a fishing spider watches carefully, calculating the right time to attack. What is the spider's launching spot? It's not a twig or lily pad, but the surface of the water itself. Why is the fishing spider able to remain suspended on the surface of the pond? Again, it is because of water's polar nature. When a molecule of water is surrounded by other water molecules, it is equally pulled in all directions by the hydrogen bonds between the molecules. But water molecules on the surface have no water molecules above them, so they are attracted to the molecules next to them and below them. This gives the bonds of the top layer of molecules a particular strength. This phenomenon is called surface tension. While the surface of water can't hold much weight, water does have a high surface tension compared with other liquids.

Tenebrionid Beetles

Tenebrionid beetles use their body to collect water from the fog that blankets the desert in the morning, and then they stand on their head to allow the water to trickle into their mouth.

Water is a universal solvent.

The action of all minerals, foods, and ions—you name it—takes place in an environment that is basically water, an aqueous Opens in modal popup window environment. Water in these environments is a solvent. A solvent is a material that causes another to dissolve within it to make a solution. The dissolved material is called a solute. Seawater is a solution. The solvent is water, and many materials or solutes are dissolved in it. Because of its polar nature, water can dissolve many materials extremely effectively, and is therefore dubbed nature's universal solvent. Water dissolves more types of solutes than any other substance on earth.

The building blocks of carbohydrates are single sugar molecules, or monosaccharides.

The basic unit of all carbohydrates is a single sugar called a monosaccharide. Mono- means one, and -saccharide means sugar. Glucose is a common monosaccharide. On the right is an example of the chemical structure of a glucose molecule. Single sugars like glucose usually have 5 or 6 carbon atoms (C) that are formed in a ring structure. Notice the chemical formula for this monosaccharide: C6H12O6. To draw that sugar ring, scientists often use shapes such as pentagons or hexagons. At each corner of the shape, there is a carbon atom. In some cases, the carbon atoms are left out of the drawing as a matter of shorthand. Turn to page 28 in your reference book to read more about monosaccharides.

Fats and oils are energy-storage lipids.

The blackpoll warbler is a tiny bird that undergoes an incredible transformation every fall. It eats enough food to double its body weight in just a few weeks, with all that additional weight stored as fat. It relies on those fat reserves as fuel for its annual migration, a trek that takes it from New England to the Caribbean—a distance of nearly 4,000 km, which the bird travels in one continuous 90-hour flight. Why would the blackpoll warbler store all that energy as fat, instead of a carbohydrate like glycogen? Per unit volume, fat is lighter in weight than carbohydrates. And, a given volume of fat contains twice as much chemical energy (the energy of chemical bonds) as the same volume of carbohydrates—another bonus for a tiny bird trying to maximize its energy-storage potential. All this fat is converted to glucose as part of the bird's metabolism, but fat is excellent for storing chemical energy. The blackpoll warbler stores energy in the form of fat for its annual migration.

Sickle-Cell Anemia

The changes in the primary structure of hemoglobin that cause sickle-cell anemia affect all levels of protein structure, including the quaternary structure.

The Fever Bark Tree

The cinchona, or fever bark tree, is native to South America. Carolus Linnaeus chose the genus name in honor of the countess of Cinchon, wife of the viceroy of Peru. The term quinine comes from the Inca, the native people of Peru, who called the tree quina-quina, which means "bark of barks."

Loss of species is a loss of potentially beneficial compounds.

The compounds you have just learned about are only a few of the many natural chemicals that can be beneficial to humans. Years of scientific experiments have yielded the wide variety of medicines we use today, but there are many more yet to be discovered and studied. Unfortunately, as the world's population increases, many species are becoming extinct as their habitats are destroyed. Plants that might be the source of medicinal compounds are being destroyed as well. Extensive logging projects, for example, eliminated 90 percent of the Pacific yew population before scientists realized the tree's value. With the destruction of rain forests and coral reefs, many living things that have the potential to benefit humanity are being lost forever.

Bird Migration

The internal organs of some birds actually shrink to make room for all the fat reserves they need to build for migration. When they land at their destination, they have to wait for their stomachs to regrow before they can begin feeding.

Enzymes recognize and interact with specific molecules.

The lactase enzyme recognizes and breaks apart a lactose molecule, but lactase doesn't interact with other sugars or other molecules like proteins or fats. This enzyme specificity is another important aspect of enzyme biology: Enzymes recognize and bind to specific molecules. Enzyme specificity explains why your body contains so many enzymes. You have digestive enzymes that recognize specific sugars, fats, or proteins. Some protein-digesting enzymes are so specific that they recognize only certain amino acids. Enzymes do more than digest your food, however. Enzymes also play roles in building the structural proteins that make up your body and help your body quickly get rid of extra carbon. Still other enzymes function in photosynthesis, helping plants produce sugars. The many roles that enzymes play make them essential in maintaining homeostasis.

Cohesion and adhesion are results of hydrogen bonding.

The last adjective you might think of when describing water is sticky. But on the molecular level, water molecules stick to each other and to many other things. This tendency of water molecules to stick together is called cohesion. Cohesion Opens in modal popup window is an attraction between the same kinds of molecules or substances. When a molecule of water is surrounded by other water molecules, it is equally pulled in all directions because of the electrical attraction between the hydrogen atoms and the oxygen atoms. Since water molecules have an electrical charge, they are also attracted to any other substance or material whose molecules have any hint of electrical charge. This phenomenon is called adhesion. You can observe adhesion in action when you see a surface covered with condensation, such as a spiderweb covered with dew. The spiderweb has a slight electrical charge, and the partially charged water molecules are attracted to it.

Small traces of various atoms can be found in several organic compounds. Organic Compounds contain carbon and Hygron and may also contain O,N,P,S,NA,Cl, K or trace elements like Fe, Mg, Zn, Co

The main atoms in organic compounds are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), sulfur (S), sodium (Na), chlorine (Cl), potassium (K), and calcium (Ca). The compounds these atoms make up are organized into four main groups—carbohydrates, lipids, proteins, and nucleic acids. But other types of atoms, some of which are metals, play an integral part of some very critical organic compounds.

Glucose is the main carbohydrate converted into energy by living things. Glucose often bonds with itself and other monosaccharides to form many other types of carbohydrates.

The monosaccharide glucose is central to all living things. Pay close attention to this molecule, as it will reoccur throughout this course in key places. Glucose has a chemical formula of C6H12O6 and exists in two main structural forms: a boat shape and a chair shape. Use the gallery to better understand this three-dimensional concept. So far you've learned that carbohydrates are broken down to generate energy. This process begins with glucose molecules, which makes them extremely important. In fact, a body coverts carbohydrates, fats, and proteins into glucose so usable energy can be produced. The word food in its most basic sense means glucose.

Plants store glucose as starch.

The potato fields of Idaho are powerhouses of photosynthesis, using the energy of the sun to produce glucose. Glucose is the sugar that is the key molecule in delivering chemical energy to cells. Plants often make more glucose than they immediately need. So what do potato plants do with all the glucose they produce during photosynthesis? Many plants store extra glucose as a molecule called starch Opens in modal popup window . Starch is a complex carbohydrate made of hundreds of units of glucose linked together in a specific way. Because starch is made of glucose, you may think of it as stored chemical energy inside a plant. Plants store glucose as starch during times when energy is abundant. When energy is scarce, they may break down their starch, releasing glucose that then becomes available for the process of cellular respiration. When you eat plant parts where starch is stored—such as oats, potatoes, or rice grains—you eat this starch. Your body then breaks it down into individual glucose molecules.

A protein's tertiary structure takes on bends and folds.

The protein keratin contains the amino acid cysteine. Cysteine is unusual in that it contains sulfur in its R-groups. The sulfur atoms can bond with one another to form disulfide bridges, which give extra strength to the keratin in your hair. That type of bond between amino acid R-groups gives rise to a protein's tertiary structure. Tertiary structure is the third level of protein structure. The polypeptide chains of many proteins bend and fold in certain places, contributing to the overall shape of a protein. Many proteins take on a globular tertiary structure. Others take on a barrel shape, or even a helix. The shape of a protein is essential to its functioning properly. The polypeptide chains of many proteins bend and fold in certain places, resulting in a tertiary structure.

More than 30 enzymes contain copper.

The same copper that pennies are made of is present in living things in small amounts. Copper (Cu) is part of the structure of more than 30 enzymes, including the enzyme lysyl oxidase. Lysyl oxidase is necessary for building and maintaining healthy connective tissue. Among its most important roles is keeping the connective tissues of your heart and blood vessels in good working order. When you look at this diagram of your circulatory system, which includes your heart and blood vessels, be aware that copper—which we take in with a normal healthy diet—is important in maintaining your whole body's state of wellness. Lysyl oxidase, which contains copper (Cu), helps maintain the health of connective tissues such as those in your heart and blood vessels.

2.19 ATP ATP is a molecule that stores and provides energy for all of life's processes.

The seven characteristics of living things are cellular organization, metabolism, homeostasis, reproduction, growth and development, response, and heredity. Each of these characteristics and the processes behind them—such as cell division, cellular respiration, movement, and photosynthesis—require energy. The chemical energy that powers these processes in living things is the molecule adenosine triphosphate (ATP). ATP is produced during the cellular pathways that break down the molecule glucose. Cells produce and use ATP in many different ways, which you will learn more about during this lesson. ATP molecules provide most of the energy for powering the biological processes necessary to sustain life.

Covalent bonds form when atoms share electrons.

The strongest type of bond is a covalent bond Opens in modal popup window . In a covalent bond, neither atom gains or loses electrons—they share them. The shared valence electrons bind the atoms together. A single atom can form covalent bonds with several other atoms at a time. A molecule of water is one example. In this example, two hydrogen atoms (H), each with 1 electron, share their electrons with an oxygen atom (O), which has 6 valence electrons, to form a water molecule. The chemical formula for a molecule of water is H2O, showing that 2 atoms of hydrogen (H2) have bonded to 1 atom of oxygen (O). Explore the process of a covalent bond forming between two hydrogen atoms and an oxygen atom.

ATP is made from other chemical components.

The structure of ATP may look somewhat familiar to you. And, if you read its name carefully— adenosine triphosphate —you might see part of a word you learned in the previous lesson. The molecule ATP consists of the nitrogenous base adenine, the sugar ribose, and three additional phosphate groups, or units made of a phosphorus atom (P) surrounded by four oxygen atoms (O). Click on The Structure of ATP. Do you recognize the adenine unit in the structure of ATP? This ATP molecule contains three phosphate groups, hence the name triphosphate. The tail of phosphate groups extends from one side of the molecule. The unit consisting of adenine and ribose is called adenosine. Review the structure of ATP in the online activity. When you have finished, turn to page 44 of your reference book to learn more about the structure of ATP.

Proteins have four levels of structure. Primary: sequence of amino acids Secondary: Hydrogen bonds between amino acids Tertiary: Bonds between functional groups Quaternary: Interaction between polypeptide chains

The structure of a protein at each level plays an important role in determining the protein's function.

Nucleic acids contain several types of nitrogenous bases.

The sugar and the phosphate group in a molecule of DNA are identical from one nucleotide to the next—the sugar always is deoxyribose and the phosphate group always contains phosphorus (P) and oxygen (O) atoms. The same holds true for a molecule of RNA, except that the sugar in every nucleotide is ribose. Nitrogenous bases, however, may differ from one nucleotide to the next. DNA contains four different nitrogenous bases: adenine, thymine, cytosine, and guanine. Chemically they are classified into two groups. Adenine and guanine are called purines. As shown here, those bases have two rings of carbon (C) and nitrogen (N). Thymine Opens in modal popup window and cytosine are classified as pyrimidines—bases with only one ring of carbon and nitrogen.

Cells use and produce ATP.

The sun shines down and a plant makes glucose. Then the energy in the bonds of glucose is transferred to the bonds in an ATP molecule. ATP is produced as an end result of breaking down a glucose molecule, which occurs through several different cellular processes. ATP may be the motor of the cell, but there appear to be no organisms on earth that make ATP directly. ATP must be made from the energy that is in the bonds of glucose molecules. But, even the first step in breaking down glucose requires ATP. Ultimately, the breakdown of glucose produces more energy—in the form of ATP—than it requires. All that ATP is used to drive the activities of a cell and must be constantly produced. You'll learn more about the specifics of ATP synthesis and breakdown in another lesson.

Phospholipids form cellular membranes.

The tenebrionid beetle lives in the Namib Desert, one of the driest places on earth. Like all living organisms, this beetle depends on chemical reactions that take place in a water solution to stay alive. How do organisms like the tenebrionid beetle maintain the aqueous environment required for metabolism? By containing that environment inside its cells. All organisms are composed of structures called cells. A cell maintains a constant internal environment, relative to the external environment. In other words, the cell is key to maintaining homeostasis. But how do cells maintain a specific internal environment? The outer membrane of a cell comprises a dual layer of lipids called phospholipids. The structure of this layer helps the cell maintain a constant internal environment—one of the key requirements for homeostasis. The phospholipids in this beetle's cells allow it to maintain the aqueous environment required for metabolism.

Blubber

The thick layer of fat under the skin of some animals is called blubber. Blubber not only stores energy, but it also serves as insulation and conserves body heat.

The energy of ATP is stored in the chemical bonds in its phosphate tail.

The triphosphate tail of an ATP molecule is its energy storehouse. To release energy, ATP is broken down from the tip of its tail by removal of one phosphate group at a time, in a reaction called hydrolysis. Hydrolysis of ATP produces a free phosphate group and a new molecule, adenosine diphosphate Opens in modal popup window (ADP). That reaction releases energy. Its energy drives many chemical reactions within a cell. Cells can also make ATP from ADP by using energy to reconnect a phosphate group. In this way, ATP is regenerated for use again by a cell. The process of connecting that phosphate group is complex, and you will learn more about it in another lesson.

Human Body, Earth's Crust

The two most abundant elements in the human body are oxygen and carbon. The two most abundant elements in the earth's crust are oxygen and silicon.

Humans have been using natural compounds to treat ailments since before recorded history. Origins of Natural Medicine North America Early European explorers learned about medicinal plants from Native Americans. One herb in particular, ginseng, quickly became a valuable commodity in world trade. Greece In the 6th century BC, Diocles of Carystys, a pupil of Aristotle, compiled one of the earliest books on the treatment of illnesses with natural substances. Another Greek, Hippocrates (470 to 377BC), is considered the father of Western medicine. He studied traditional remedies from Africa and Babylon, and his writings describe 236 plant drugs Sumeria The first written records detailing the use of plants for treating ailments are Sumerian clay tablets created around 2000 BC. The writings name 250 herbs as medicines. Middle East Early Muslim knowledge of natural medicines centered on the writings of Jami of Ibn Blaier, compiled about AD 1230. He described more than 2000 natural medicinal substances. Christian doctors traveling to Jerusalem with the Crusaders brought the knowledge of natural medicine back to Europe. Trade During the Middle Ages international commerce along the Silk Road included the trade of herbs and natural medicinal compounds. India About 2500 years ago in the region that is now India, Ayurvedic medicine emerged along with schools of religious thought such as Hinduism and Buddhism. The most important book on medicine was the Characka Samhita, which detailed the use of 582 herbs. China The earliest written evidence of the medicinal use of herbs in China is a group of volumes written on silk from the 3rd century BC. The writings name more than 250 medicinal substances, most from plants.

The use of plant compounds for health purposes is older than recorded history. In the United States, the words food and medicine conjure up unrelated images, but in most of the world, the line between food and medicine is often not clear. Today, 80 percent of the world's population uses plant compounds as a primary source of medication. When you pick up a prescription at a pharmacy, there is a one-in-four chance the active ingredient in the medicine comes from plants. Explore some of the places in the world where the use of natural compounds as medicines originated.

Proteins provide structure and support.

The world's largest animal—the blue whale, which grows up to 30 m long—feeds on some of the world's smallest animals—tiny invertebrates called krill. The blue whale dives deep into the ocean and swims into huge schools of krill, taking into its mouth a huge quantity of krill and ocean water. The whale then strains the water against plates in its mouth called baleen. Water filters through the baleen, but the krill remain behind and are swallowed. Baleen are made of a structural protein called keratin—the same protein that makes up your hair and fingernails. Keratin forms many important support structures throughout the animal kingdom, including bird beaks and feathers, reptile scales, turtle shells, and insect exoskeletons. Collagen is another important structural protein. It is the main component of many tissues in your body, such as bones, teeth, cartilage, and tendons. Like keratin, its structure accounts for many of its properties.

Carbon exists in many forms on earth.

There are close to 10 million known carbon compounds in the universe. Most are organic compounds—the compounds most often associated with life. But some carbon compounds are inorganic compounds. Familiar inorganic carbon-based compounds include fossil fuels like natural gas, coal, and oil. Carbon monoxide (CO) is a poisonous gas that is emitted when those fuels burn. A valuable diamond is made of pure carbon, as is the graphite in an ordinary pencil. With its 4 valence electrons, carbon is able to bond in many ways to form both organic and inorganic compounds. Carbon atoms are recycled again and again in numerous ways between organic and inorganic states. Do you see why scientists consider carbon so important in our lives?

2.13 Complex Carbohydrates Complex carbohydrates are polysaccharides and are made up of many simple carbohydrate molecules linked together.

There's nothing quite like hot mashed potatoes in the middle of winter. But did you ever think about what that potato is made of? Potatoes—and many of the other fruits and vegetables you eat—contain organic molecules called complex carbohydrates, which are polysaccharides. You may have heard of some of these complex carbohydrates, such as starch and cellulose. But what are they, exactly? Starch, cellulose, and another complex carbohydrate called glycogen are large molecules made of hundreds, or even thousands, of glucose molecules held together in different ways. These molecules store energy and provide strength and support to living things. Turn to pages 30 and 31 of your reference book for additional information as you complete this lesson.

2.03 Carbon and Life Organic compounds contain carbon.

Think about the iridescent feathers of a peacock, the rough bark of a tree, the deadly venom of a king cobra, the soft skin of a baby. All of those things are matter, and all matter is made of the atoms of elements. How many different elements would have to combine to produce the huge variety of characteristics of all living things on earth? Every element in the Periodic Table? The striking truth is that, when it comes to living things, only a small handful of elements come into play. In the vast theater of life, one element in particular is a celebrity-carbon. Carbon atoms are the building blocks of every molecule that is essential to life. Carbon-based molecules that are present in living things are called organic compounds Opens in modal popup window .

Scientists isolate and study chemical compounds in living things.

Though people have been using natural chemical compounds as medicines for years, it wasn't until the early nineteenth century that scientists began studying the effects of individual compounds. While scientists understand that most plant substances do not work in isolation to cure an ailment, they have determined the effects of thousands of specific molecules that come from plant substances. Some natural compounds can be both beneficial and harmful to humans, and chemists must first alter them to remove the harmful substances. Others scientists use natural substances as models to make synthetic versions. In the early nineteenth century, scientists began studying natural compounds used as medicines.

Deoxyribose and ribose are monosaccharides found in DNA and RNA, respectively.

Two wild dogs frolic in the dust of an African plain. Speckled black and beige, each dog has a unique coat pattern determined by its genetic code. Genes, which transfer traits from parent to offspring, are part of an organism's deoxyribonucleic acid (DNA). Integral components of the molecules DNA and ribonucleic acid (RNA) are the sugars deoxyribose and ribose, respectively—both monosaccharides with five carbon atoms. Nucleic acids are the molecules that contain and implement genetic control over the cell. DNA contains the instructions for building proteins; RNA is integral to the synthesis of those proteins. Monosaccharides are an essential part of both.

Unsaturated fats have double bonds between carbon atoms.

Unsaturated fats, many of which are found in plant products, have a double bond between some carbon atoms in the fatty acid chain. That double bond takes up two available bond spaces, leaving space for only one hydrogen atom on a double-bonded carbon. Because hydrogen atoms do not fill all the available bond spaces, those fats are unsaturated. Double bonds produce bends or kinks in the fatty acid chain. Those kinks keep unsaturated fats from stacking together as smoothly as saturated fats. Scientists suggest that the lack of ability to pack together may cause unsaturated fats to build up less slowly in blood vessels than saturated fats. Saturated fats, such as animal fats, tend to be solid at room temperature, while unsaturated fats, such as corn oil and olive oil, are usually liquid at room temperature.

Living things have adapted different ways to keep the proper balance of water.

Water is so important that the cells of living things must maintain certain levels of water at all times. A plant cell stores excess water in a structure called a central vacuole, which releases water as needed. The single-cell paramecium, which lives in water, has a structure called a contractile vacuole, which can squeeze out excess water. The desert-dwelling kangaroo rat can go months without drinking water; it reabsorbs water from its own organs and extracts water from the foods it eats. Whatever the mechanism, all living things must keep the proper balance of water so their cells can maintain an aqueous environment.

Everything is made of matter.

What do popcorn, soft drinks, clouds, a tree, a car, and your body have in common? The answer is they are all matter Opens in modal popup window . Matter is everything in the universe that takes up space and has mass. Even things that you can't see—such as air, viruses, and water vapor—are matter.

Hydrogen

What is the most abundant element in the universe? Scientists think that hydrogen makes up more than 75 percent of the matter in the universe.

All matter tends toward unorganized states.

When bonds form, the chemical world is building on itself to create a more organized system of matter. There is a flip side to this process. A lot of matter starts out as or becomes part of a precise, neatly built unit such as a butterfly or tree, or even a brand new sports car or a new pair of jeans. What happens to all of those things over time? Without a doubt, they will all die, rust away, or fall apart. All biological organisms decay and decompose. Over time, all organized matter—such as the butterfly, tree, car, and jeans—tends to become unorganized. This concept is called entropy Opens in modal popup window . Here's another way to understand entropy. Think of a deck of cards. If you threw an entire deck of cards into the air, what are the chances it would land back in a neat stack? In numerical order? Into suits? Impossible, right? Matter is similar. It tends toward unorganized states—it tends toward entropy.

The specific shape and structure of an enzyme's active site determine the molecules with which it can interact.

When bound together in this way, the enzyme catalyzes a reaction, such as breaking apart the substrate molecule. The end result of an enzyme-catalyzed reaction is called the product. In the earlier example, the lactose substrate binds to the lactase enzyme to form an enzyme-substrate complex, which has the products galactose and glucose. Once the lactose molecule is broken apart, the products leave the enzyme, and the enzyme is free to interact with other molecules. In a given enzyme, the active site has a specific shape and structure, into which only certain molecules can fit. For example, a cellulose molecule would not fit in the lactase enzyme's active site.

Steroids are lipids that include carbon rings.

When male and female chimpanzee embryos first begin to develop, they look identical. After several weeks, however, the male embryos begin to produce a molecule called testosterone. This molecule directs the development of male reproductive organs in the embryo. Female embryos do not produce this molecule; therefore, they develop differently from male embryos. Testosterone is one type of steroid. Steroids are a class of lipids that contain ring structures made of carbon. One steroid you may have heard of is the molecule cholesterol. While it receives attention because of its association with conditions such as heart disease, cholesterol is an important component of many cellular structures. Your body also uses cholesterol to make testosterone and other steroids like estrogen.

Water molecules are joined by hydrogen bonds.

When several water molecules bond together, they don't do so randomly. Because water is a polar molecule, the electrical charges align in certain positions. The negatively charged oxygen atoms attract the positively charged hydrogen atoms, forming a hydrogen bond. Recall that a hydrogen bond is weaker than either an ionic bond or a covalent bond. Turn to page 42 in your reference book to read more about water molecules and how they form hydrogen bonds.

Proteins defend the body from disease.

When you catch a cold at the beginning of the school year, your body learns to recognize the virus that caused you to become ill. Later that year, if one of your friends or siblings catches the same cold, you probably won't because your body has built up immunity to it. In other words, your body recognizes the virus as foreign and can quickly mount an attack against it. That immunity comes about thanks to the activity of still another class of proteins called antibodies. Antibodies are defense proteins that the body produces in response to invading pathogens, such as bacteria and viruses. Invading pathogens cause the body to produce antibodies, which are defense proteins.

Carbon has unique bonding abilities.

When you were younger, did you have a set of building blocks? If so, you probably remember certain blocks you always started with. You used them to build the base of your structure, and you connected all of the other blocks to them. Carbon is like those base building blocks. Carbon has 4 valence electrons, so it has 4 available spaces in its outer level for bonding. Carbon can easily form 4 covalent bonds with other atoms, including carbon atoms. A single carbon atom (C) can bond covalently with four hydrogen atoms (H) to form a methane molecule (CH4). Carbon has 4 empty spaces for valence electrons. Hydrogen has one empty space for valence electrons. Note that the bond forms among the valence electrons.

ATP powers muscles in the body.

Whether you're just climbing into bed for a good night's sleep or getting ready for a 5-km run, you use ATP as the primary source of energy for the work that your muscles perform. ATP provides the energy required for your muscles to contract. It would be nearly impossible for muscle cells to store enough ATP to power motion that lasts more than just a few seconds. For this reason, ATP is constantly produced in muscle cells as they perform work. The processes of cellular respiration and glycolysis provide the ATP for your muscles; you will learn more about both processes in the next unit. While all cells require ATP to function, muscle cells need an exceptionally large amount of ATP to power the chemical and physical changes involved in muscle contraction.

Humans can benefit from chemical compounds in living things.

While this lesson touched on several compounds produced by plants, other living things—such as sea creatures, insects, and animals—also produce chemicals useful to humans. In many cases, a compound produced by a plant or animal for its own protection can become a potent medicine for humans.

The cellular environment is aqueous.

Why do living things need so much water, and so often? One reason is the structure of the cell environment. All processes and chemical reactions that keep you alive take place in your cells. For example, every piece of your body was made within the microscopic workshops of your cells. The enzymes in your saliva, hair, hormones, and thousands of proteins are made inside cells. Cells are filled with fluid, and the fluid is aqueous. The energy you need for every single action is generated in the aqueous environment of your cells. Cells are filled with fluid, and the fluid is aqueous.

Disaccharides such as sucrose result when two monosaccharides form a chemical bond.

With a smile, a delighted mother opens her gift—a box of gourmet chocolates. She carefully selects a round, dark piece and enjoys the sucrose-filled treasure. Sucrose Opens in modal popup window is the chemical name for table sugar, and it is widely used as a sweetener. When you eat sweet things, sucrose is most likely making it sweet. Sucrose is composed of a glucose molecule and a fructose molecule bonded together. When a carbohydrate is made of only two simple sugars like sucrose, it is a disaccharide Opens in modal popup window . Di- means two. Most plants do not make sucrose, but the ones that do—such as sugarcane and sugar beets—are very important commercially. Sucrose is harvested naturally from these plants.

Proteins provide storage and help transport materials throughout the body.

With every breath you take, you're bringing oxygen into your body. Your body uses that oxygen in many important chemical reactions, but how does oxygen get from your lungs to all parts of your body? A specialized protein called hemoglobin is present in your blood, and it picks up oxygen in your lungs and delivers it throughout your body. Each hemoglobin molecule contains an iron atom, which binds to the oxygen. Because it holds onto oxygen molecules in this way, hemoglobin is a transport protein—it transports oxygen through your body. Iron is an essential nutrient that you get from eating meats, beans, and some kinds of fruits and vegetables. Your body uses iron to make hemoglobin, but your body also can store iron for future use in a storage protein called ferritin. Ferritin stores iron so that it is available for hemoglobin production even during times when your body doesn't have enough iron.

Water is a critical component of all living things largely because of its unique physical characteristics and properties. Water is a universal solvent because of its polar nature which allows cohesion and adhesion. Water forms an aqueous environment that is the basis for all cell processes.

Without water, life is not possible. Living things are made from cells, and cells are made mostly of water. The chemical structure of water as a polar molecule gives water many unique characteristics—many of which are based on the hydrogen bonding between water molecules. A balance of water is also critical to the survival of any organism. Keeping the right level of water and dissolved materials is necessary for cellular processes to occur properly. Later in the course, you will learn how water perpetually cycles between living and nonliving things.

A protein's shape influences its activity. Immunoglobulin functions as part of the immune system, attacking harmful substances in the body. Hemerythrin is the oxygen-carrying protein in many invertebrates. Scorpion neurotoxin attacks nerve cells after a scorpion bites. Glucagon plays a major role in regulating the level of sugar in a person's blood. Pepsin breaks down proteins in the stomach so they can be digested.

You don't need to know the names of all of the proteins or what they do, but you should know that no two are the same. Of the millions of proteins that function in living things, each has to have a particular shape to perform its function.

A protein's quaternary structure is the way that polypeptide chains bind and interact.

You have already learned that a protein is made up of two or more polypeptide chains. Those chains, sometimes called subunits, interact with one another in a way that brings about the highest level of protein structure, protein's quaternary structure. The molecule hemoglobin provides a good example of quaternary structure. Hemoglobin consists of four polypeptide chains that are held together by many types of intramolecular forces, such as hydrogen bonds or hydrophobic interactions. The highest level of protein structure is its quaternary structure.

Organic compounds are made primarily from only a few elements. Elements in the Human Body http://web2.iadfw.net/uthman/elements_of_body.html

You may recall from the previous lesson that there are four major groups of organic compounds in living things—carbohydrates, lipids, proteins, and nucleic acids. Those compounds are made primarily from carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), sulfur (S), and calcium (Ca). Your body is composed of these and other elements in different proportions. Visit Elemental Composition of the Human Body to see the proportions of elements in your body. There are many other elements that living things depend on for survival. Those elements exist in very small amounts compared to the ones mentioned above, but their roles are significant nonetheless.

About 20 amino acids exist in nature and make up all proteins in living organisms. Amino Acids Glycine Alanine Proline Valine Isoleucine Leucine Methionine Tryptophan Phenylalanine Tyrosine Threonine Cysteine Asparagine Glutamine Serine Asparatic Acid Glutamic Acid Lysine Arginine Histidine

Your body contains tens of thousands of proteins, which play roles in structure, support, metabolism, homeostasis, and defense from disease, as well as other functions. This great diversity in protein structure and function comes from a group of about 20 amino acids. In other words, all proteins found in living organisms are composed of about 20 different amino acids. The amino acids are arranged in different combinations to make up different proteins. Let's look closely at amino acids. The different properties of the R-groups in amino acids affect the chemical and physical properties of the proteins they eventually become part of. Some R-groups are nonpolar and hydrophobic. Others are polar and hydrophilic. Some also have a positive or negative charge; these amino acids are attracted to water as well.

Carbon is present in carbohydrates.

Your body is made of carbon-based molecules, which are used in many ways. Much of the food you eat is made of carbon compounds. Plants, for example, contain a lot of carbohydrates, and all carbohydrates contain carbon, hydrogen, and oxygen atoms that are bonded together by valence electrons. Potatoes are loaded with a carbohydrate called starch. Each starch molecule is made up of many smaller carbohydrates, each of which is called glucose. Glucose is one example of a carbohydrate. Rice, bread, pasta, french fries—any plant-based food contains carbohydrates. When you eat foods that contain carbohydrates, your body uses a complex process to turn the carbohydrates into useful energy.

A protein's secondary structure is formed by hydrogen bonds between amino acids in a polypeptide chain.

Your hair is made primarily of the protein keratin. Some regions of the polypeptide chains in this protein take on a twisting shape called an alpha helix. That twisting of the polypeptide chain is called the protein's secondary structure. Most proteins have two types of secondary structure: The chain takes either the shape of an alpha helix or the shape of a beta-pleated sheet. A beta-pleated sheet looks like back-and-forth folds in a sheet of paper. Look at both shapes on the right.

Covalent Bond Why call this type of bond a covalent bond? The prefix co- means to share. The suffix valent refers to the valence electrons of the two atoms. Put the two word parts together and you have covalent: to share valence electrons.

a bond in which electrons are shared between the bonded atoms Ex. H2O

Polysaccharide

a carbohydrate composed of many simple sugar molecules bonded together in an unbranched or branched chains

Enzymes

a catalyst for chemical reactions within living things, increasing the rate of the reaction without being changed itself

glycogen

a complex, highly branched polysaccharide that is formed from glucose subunits, found in vertebrates, and used for energy storage

Inorganic Compound

a compound not formed from carbon-hydrogen bonds; more generally, a compound not produced by a living thing

Hemoglobin

a large molecule that captures oxygen from the lungs and delivers it to the rest of the body

macromolecules

a large molecule, especially applied to carbohydrates, proteins, lipids, and nucleic acids

Clorophyll

a molecule in plants that plays a key role in photosynthesis

polar molecule

a molecule in which there are positive and negative areas

Glucose

a monosaccharide with the chemical formula C6H12O6 used by cells for energy

Neutrons

a neutral particle with approximately the same mass as a proton, found in nuclei of atoms along with protons

Protons

a positively charged particle found in the nuclei of atoms A proton has 1,836 times more mass than an electron.

Electron

a tiny part of an atom with a negative electrical charge

Atom

a tiny particle that is the fundamental building block of all substances and whose properties determine the properties of an element made up only of those atoms

Ions

an atom that has a positive or negative electrical charge

Cellulose

an unbranched polysaccharide, formed from glucose subunits, found in plant cell walls, used for structural support

Organic Compound

any chemical compound that contains carbon bonded to at least one other atom, usually hydrogen

Organic compounds

any chemical compound that contains carbon bonded to at least one other atom, usually hydrogen The term organic compound was first used to describe substances that came directly from living things. Then a scientist was able to synthesize one of those substances in a lab. Today the term organic compound applies to any compound that contains carbon-hydrogen bonds.

Molecules

any compound resulting from covalent bonding

Lipid

fats, oils, phospholipids, steroids, and waxes; one of four major classes of large organic molecules

A protein is made of one or more polypeptide chains.

he fer-de-lance has proteins in its venom called cytotoxins, which are materials that kill cells. It bites a mouse, whose bloodstream carries venom throughout its body. Cytotoxins break down its cells from the inside, making an easy meal for the fer-de-lance. Like all proteins, the cytotoxins in snake venom are composed of polypeptide chains. Those chains twist and fold together to give the protein a complex shape and structure. Those physical characteristics affect how proteins function in living organisms. Polypeptide chains twist and fold together to give proteins complex shapes and structures.

Bioluminescence

light produced by a living organism

steroid

lipid molecules that are hormones or structural elements in cell membranes

phospholipid

lipids that make up the main structural element of biological membranes

Carbohydrates

one of the four major classes of large organic molecules made from carbon, oxygen, and hydrogen

Proteins

one of the four major classes of large organic molecules, made of amino acids

Nucleic Acids

one of the four major classes of large organic molecules, which are important in storing, transmitting, and making useful the information necessary for the processes of life

quaternary structure

the association of two or more polypeptide chains in a spatial relationship to make up a protein

secondary structure

the coiling or folding of a polypeptide in which amino acids near one another in the chain bond When you wet your hair, water molecules disrupt some of the hydrogen bonds that form keratin's secondary structure. If you style your hair while it is wet, the hydrogen bonds between amino acids will re-form as water evaporates. These new bonds will hold your hair in a new shape...until you wash it again.

phospholipid bilayer

the double layer of phospholipids that makes up the membranes of a cell

Valence Electron

the electrons in any atom´s outer orbital path

Activation Energy

the energy barrier that must be overcome for a reaction to occur

tertiary structure

the folding of a polypeptide with secondary structure in which amino acids far apart from one another in the chain bond

Iconic Bond

the force of attraction between a charged atom (or group of connected atoms) and another with the opposite charge

Hydrogen Bond

the force of attraction between a partially charged atom and a hydrogen atom that is covalently bonded to another partially charged atom

Primary Structure

the order of amino acids that makes up a protein or polypeptide

Amino Acids

the organic molecules that serve as the units from which proteins are made

Entropy

the randomness of any physical system

hydrophobic

water hating; not soluble in water

hydrophilic

water loving; soluble in water