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Human Physiology 6/e Fox | |||||
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Chapter Summary |
Chapter 2: Chemical Composition of the Body |
Atoms, Ions, and Chemical Bonds
I. Covalent bonds are formed by atoms that share electrons. They are the strongest type of chemical bond.
A. Electrons are equally shared in nonpolar covalent bonds and unequally shared in polar covalent bonds.
B. Atoms of oxygen, nitrogen, and phosphorus strongly attract electrons and become electrically negative compared to the other atoms sharing electrons with them.
II. Ionic bonds are formed by atoms that transfer electrons; these weak bonds join atoms together in an ionic compound.
A. If one atom in this compound takes the electron from another atom, it gains a net negative charge and the other atom becomes positively charged.
B. Ionic bonds easily break when the ionic compound is dissolved in water. Dissociation of the ionic compound yields charged atoms called ions.
III. When hydrogen is bonded to an electronegative atom, it gains a slight positive charge and is weakly attracted to another electronegative atom. This weak attraction is a hydrogen bond.
IV. Acids donate hydrogen ions to solution, whereas bases lower the hydrogen ion concentration on a solution.
A. The pH scale is a negative function of the logarithm of the hydrogen ion concentration.
B. In a neutral solution the concentration of H+ is equal to the concentration of OH-, and the pH is 7.
C. Acids raise the H+ concentration and thus lower the pH below 7; bases lower the H+ concentration and thus raise the pH above 7.
V. Organic molecules contain atoms of carbon joined together by covalent bonds; atoms of nitrogen, oxygen, phosphorus, or sulfur may be present as specific functional groups in the organic molecule.
Carbohydrates and Lipids
I. Carbohydrates contain carbon, hydrogen, and oxygen, usually in a ratio of 1:2:1.
A. Carbohydrates consist of simple sugars (monosaccharides), disaccharides, and polysaccharides (such as glycogen).
B. Covalent bonds between monosaccharides are formed by dehydration synthesis, or condensation. Bonds are broken by hydrolysis reactions.
II. Lipids are organic molecules that are insoluble in polar solvents such as water.
A. Triglycerides (fat and oil) consist of three fatty acid molecules joined to a molecule of glycerol.
B. Ketone bodies are smaller derivations of fatty acids.
C. Phospholipids (such as lecithin) are phosphate-containing lipids that have a hydrophilic polar group. The rest of the molecule is hydrophobic.
D. Steroids (including the hormones of the adrenal cortex and gonads) are lipids with a characteristic five-ring structure.
E. Prostaglandins are a family of cyclic fatty acids, which serve a variety of regulatory functions.
Proteins
I. Proteins are composed of long chains of amino acids bound together by covalent peptide bonds.
A. Each amino acid contains an amino group, a carboxyl group, and a functional group. Differences in the functional groups give each of the more than twenty different amino acids an individual identity.
B. The polypeptide chain may be twisted into a helix (secondary structure) and bent and folded to form the tertiary structure of the protein.
C. Proteins that are composed of two or more polypeptide chains are said to have a quaternary structure.
D. Proteins may be combined with carbohydrates, lipids, or other molecules.
E. Because of their great variety of possible structures, proteins serve a wider variety of specific functions than any other type of molecule.
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