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.
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