Chapter Summary 2.1 The Importance of Chemistry in Anatomy and Physiology Chemicals are all around us. Household products such as soap and shampoo as well as food and medicine are comprised of chemicals. The human body is also made of chemicals. We begin our examination of anatomy and physiology with a study of basic chemistry. 2.2 Fundamentals of Chemistry Matter is anything that has mass and takes up space. 1. Elements and atoms a. Naturally occurring matter on Earth is composed of ninety-two elements. b. Elements usually combine to form compounds. c. Elements are composed of atoms. d. Atoms of different elements vary in size, weight, and ways of interacting. 2. Atomic structure a. An atom consists of electrons surrounding a nucleus, which has protons and neutrons. The exception is hydrogen, which has only a proton in its nucleus. b. Electrons are negatively charged, protons positively charged, and neutrons uncharged. c. A complete atom is electrically neutral. d. The atomic number of an element is equal to the number of protons in each atom. 3. Isotopes a. Isotopes are atoms with the same atomic number but different mass numbers (due to differing numbers of neutrons). The atomic weight of an element is the average of the mass numbers of its various isotopes. b. All the isotopes of an element react chemically in the same manner. c. Some isotopes are radioactive and release atomic radiation. 4. Molecules and compounds a. Two or more atoms may combine to form a molecule. b. A molecular formula represents the numbers and types of atoms in a molecule. c. If atoms of the same element combine, they produce molecules of that element. d. If atoms of different elements combine, they form molecules called compounds. 2.3 Bonding of Atoms When atoms form links called bonds, they gain, lose, or share electrons. Electrons occupy space in areas called electron shells that encircle an atomic nucleus. Atoms with completely filled outer shells are inert, whereas atoms with incompletely filled outer shells gain, lose, or share electrons and thus become stable. 1. Ionic bonds a. Atoms that lose electrons become positively charged (cations); atoms that gain electrons become negatively charged (anions). b. Ions with opposite charges attract and join by ionic bonds. 2. Atoms that share electrons join by covalent bonds. a. Nonpolar molecules result from an equal sharing of electrons. b. Polar molecules result from an unequal sharing of electrons. c. Hydrogen bonds may form within and between polar molecules. 3. Chemical reactions a. In a chemical reaction, bonds between atoms, ions, or molecules break or form. Starting materials are called reactants; the resulting atoms or molecules are called products. b. Three types of chemical reactions are synthesis, in which large molecules build up from smaller ones; decomposition, in which molecules break down; and exchange reactions, in which parts of two different molecules trade positions. c. Many reactions are reversible. The direction of a reaction depends upon the proportion of reactants and products and the energy available. d. Catalysts (enzymes) influence the rate (not the direction) of the reaction. 2.4 Electrolytes, Acids and Bases, and Salts Compounds that ionize in water are electrolytes. 1. Electrolytes that release hydrogen ions are acids, and those that release hydroxide or other ions that react with hydrogen ions are bases. a. Acids and bases react to form water and electrolytes called salts. 2. Acid and base concentrations a. pH represents the concentration of hydrogen ions (H+) and hydroxide ions (OH−) in a solution. b. A solution with equal numbers of H+ and OH− is neutral and has a pH of 7.0; a solution with more H+ than OH− is acidic (pH less than 7.0); a solution with fewer H+ than OH− is basic (pH greater than 7.0). c. A tenfold difference in hydrogen ion concentration separates each whole number in the pH scale. d. Buffers are chemicals that resist pH change. 2.5 Chemical Constituents of Cells Molecules containing carbon and hydrogen atoms are organic and are usually nonelectrolytes; other molecules are inorganic and are usually electrolytes. 1. Inorganic substances a. Water is the most abundant compound in the body. Many chemical reactions take place in water. Water transports chemicals and heat and helps release excess body heat. b. Oxygen releases energy for metabolic activities from glucose and other molecules. c. Carbon dioxide is produced when certain metabolic processes release energy. d. Inorganic salts provide ions needed in a variety of metabolic processes. e. Electrolytes must be present in certain concentrations inside and outside of cells. 2. Organic substances a. Carbohydrates provide much of the energy cells require and are built of simple sugar molecules. b. Lipids, such as triglycerides (fats), phospholipids, and steroids, supply energy and are used to build cell parts. 1) The building blocks of triglycerides are glycerol and three fatty acids. 2) The building blocks of phospholipids are glycerol, two fatty acids, and a phosphate group. 3) Steroids include rings of carbon atoms and are synthesized in the body from cholesterol. c. Proteins serve as structural materials, energy sources, hormones, cell surface receptors, antibodies, and enzymes that speed chemical reactions without being consumed. 1) The building blocks of proteins are amino acids. 2) Proteins vary in the numbers and types of their constituent amino acids; the sequences of these amino acids; and their three-dimensional structures, or conformations. 3) Primary structure is the amino acid sequence. Secondary structure comes from attractions between amino acids that are close together in the primary structure. Tertiary structure reflects attractions of far-apart amino acids and folds the molecule. The amino acid sequence determines the protein’s conformation. 4) The protein’s conformation determines its function. 5) Exposure to excessive heat, radiation, electricity, or certain chemicals can denature proteins. d. Nucleic acids constitute genes, the instructions that control cell activities, and direct protein synthesis. 1) The two types are RNA and DNA. 2) Nucleic acid building blocks are nucleotides. 3) DNA molecules store information that cell parts use to construct specific proteins. 4) RNA molecules help synthesize proteins. 5) DNA molecules are replicated, and an exact copy of the original cell’s DNA is passed to each of the newly formed cells resulting from cell division.

Matter

Anything that has mass and takes up space

Atoms

The smallest unit of an element

Elements

There are 92 natural occurring elements on Earth

Atoms

Atoms consists of 3 parts. Electrons neutrons and protons

Electrons

Negative charge; orbit around the nucleus

Protons

Positive charge (in nucleus)

Neutrons

Negative charge (in the nucleus)

Atomic number

Number of protons in an element

Isotopes

Atoms of the same element but with different numbers of neutrons

Molecule

Two or more atoms bonded together

Compounds

Combined atoms from different elements

Ionic bond

When one atom loses an electron and another gains it

Covalent bond

Atoms that share electrons

Non polar covalent bonds

Atoms that equally share electrons

Polar covalent bonds

Atoms that unequally share electrons

Reactants

Starting material in chemical reactions

Products

Ending products of chemical reactions

Synthesis

Building larger molecules from smaller ones

Decomposition

Breaking molecules down

Exchange

When parts of two molecules swap

Catalysts (enzymes)

Speed up reactions without being used up

Electrolytes

Compounds that ionize in water

Acids

Release hydrogen ions

Bases

Release ions that reach with H+

Salts

Form when acid and bases react

pH

Measures the concentration of H+ and OH- in a solution

pH 7

Neutral

Acidic

pH less that 7

Basic (alkaline)

pH greater than 7

Inorganic substances

Water, oxygen, carbon dioxide and salts

Organic substances

Carbon and hydrogen

Carbohydrates

Provide energy (made of simple sugars)

Lipids (fats)

Store energy and build cell parts

Proteins

Made of amino acids

nucleic acids

DNA AND RNA

Amino acids

Building blocks of proteins

Primary

Sequence of amino acids

Secondary or tertiary

How the chain of amino acid folds

Function

The structure determines the function of the protein

Heat chemicals or radiation

How proteins can be damaged

DNA

Stores genetic information

RNA

Helps make protein based on DNA instruction

Nucleotides

The building blocks of DNA and RNA

Chemistry

The foundation for understanding how the body functions