¿A- -if


© The McGraw-H Companies, 2001

m basis of understanding ^Vo rds bio-, life: biochemistry—branch of science dealing with the chemistry of life forms. di-, two: ¿¡saccharide— compound whose molecules are composed of two saccharide units bound together. glyc-, sweet: glycogen—complex carbohydrate composed of sugar molecules bound together in a particular way.

iso-, equal: isotope—atom that has the same atomic number as another atom but a different atomic weight.

lip-, fat: lipids—group of organic compounds that includes fats.

-lyt, dissolvable: electrolyte—

substance that dissolves in water and releases ions. mono-, one: monosaccharide—

compound whose molecule consists of a single saccharide unit. nucle-, kernel: nucleus—central core of an atom. poly-, many: polyunsaturated— molecule that has many double bonds between its carbon atoms. sacchar-, sugar:

monosaccharide—sugar molecule composed of a single saccharide unit. syn-, together: synthesis— process by which substances are united to form a new type of substance. -valent, having power: covalent bond—chemical bond produced when two atoms share electrons.

chapter objectives

After you have studied this chapter, you should be able to

1. Explain how the study of living material depends on the study of chemistry.

2. Describe the relationships among matter, atoms, and molecules.

3. Discuss how atomic structure determines how atoms interact.

4. Explain how molecular and structural formulas are used to symbolize the composition of compounds.

5. Describe three types of chemical reactions.

7. List the major groups of inorganic substances that are common in cells.

8. Describe the general functions of the main classes of organic molecules in cells.

he reunion of the extended Slone family in Kentucky in

Tthe spring of 1994 was an unusual event. Not only did ninety relatives gather, but medical researchers also attended, sampling blood from everyone. The reason— the family is very rare in that many members suffer from hereditary pancreatitis, locally known as Stone's disease. In this painful and untreatable condition, the pancreas digests itself. This organ produces digestive enzymes and hormones that regulate the blood glucose level. The researchers were looking for biochemical instructions, in the form of genes, that might explain how the disease arises. This information may also help the many thousands of people who suffer from nonhereditary pancreatitis.

Kevin Slone, who organized the reunion, knew well the ravages of his family's illness. In 1989, as a teenager, he was hospitalized for severe abdominal pain. When he was again hospitalized five years later, three-quarters of his pancreas had become scar tissue. Because many relatives also complained of frequent and severe abdominal pain, Kevin's father, Bobby, began assembling a family tree. Using a com puter, he traced more than 700 relatives through nine generations. Although he didn't realize it, Bobby Slone was conducting sophisticated and invaluable genetic research.

David Whitcomb and Garth Ehrlich, geneticists at the University of Pittsburgh, had become interested in hereditary pancreatitis and put the word out that they were looking for a large family in which to hunt for a causative gene. A colleague at a new pancreatitis clinic at the University of Kentucky put them in touch with the Slones and their enormous family tree. Soon after the blood sampling at the family reunion, the researchers identified the biochemical cause of hereditary pancreatitis.

Affected family members have a mutation that blocks normal control of the manufacture of trypsin, a digestive enzyme that breaks down protein. When the powerful enzyme accumulates, it digests the pancreas. A disorder felt painfully at the whole-body level is caused by a problem at the biochemical level. Researchers are using the information provided by the Slone family to develop a diagnostic test and treatments.

Chemistry considers the composition of substances and how they change. Although it is possible to study anatomy without much reference to chemistry, it is essential for understanding physiology, because body functions depend on cellular functions that in turn result from chemical changes.

As interest in the chemistry of living organisms grew and knowledge of the subject expanded, a field of life science called biological chemistry, or biochemistry, emerged. Biochemistry has been important not only in helping explain physiological processes but also in developing many new drugs and methods for treating diseases.

H Why is a knowledge of chemistry essential to understanding physiology?

What is biochemistry?

Structure of Matter

Matter is anything that has weight and takes up space. This includes all the solids, liquids, and gases in our surroundings as well as in our bodies. All matter consists of particles that are organized in specific ways. Table 2.1 lists some particles of matter and their characteristics.

Elements and Atoms

All matter is composed of fundamental substances called elements (el'e-mentz). As of early 1998, 112 such elements are known, although naturally occurring matter on earth includes only 92 of them. Among these elements are such common materials as iron, copper, silver, gold, aluminum, carbon, hydrogen, and oxygen. Some elements exist in a pure form, but these and other elements are more commonly parts of chemical combinations called compounds (kom'-powndz).

Elements required by the body in large amounts— such as carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus—are termed bulk elements. These elements make up more than 95% (by weight) of the human body (table 2.2). Elements required in small amounts are called trace elements. Many trace elements are important parts of enzymes, which are proteins that regulate the rates of chemical reactions in living organisms. Some elements that are toxic in large amounts, such as arsenic, may actually be vital in very small amounts, and these are called ultratrace elements.

Elements are composed of particles called atoms (at'omz), which are the smallest complete units of the elements. The atoms that make up each element are chemically identical to one another, but they differ from the atoms that make up other elements. Atoms vary in size, weight, and the way they interact with one another. Some atoms, for instance, can combine either with atoms like themselves or with other kinds of atoms.

Atomic Structure

An atom consists of a central portion called the nucleus and one or more electrons that constantly move around the nucleus. The nucleus contains one or more relatively large particles, protons and usually neutrons, whose weights are about equal, but which are otherwise quite different (fig. 2.1).

Electrons, which are so small that they have almost no weight, carry a single, negative electrical charge (e-). Each proton carries a single, positive electrical charge (p+). Neutrons are uncharged and thus are electrically neutral (n0).

Because the nucleus contains protons, this part of an atom is always positively charged. However, the number

hM Some Particles

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