Organization of the Body
Many amino acids joined by peptide bonds form a polypeptide.
A protein (one or more polypeptides) is distinguished by the
number and sequence of amino acids in its chain(s) and by the
complexity of its three-dimensional structure.
Fibrous proteins, such as keratin and collagen, have secondary
-helix or β-pleated sheet) and perhaps tertiary and quaternary
structure. Fibrous proteins are used as structural materials.
Globular proteins achieve tertiary and sometimes quaternary
structure and are generally spherical, soluble molecules. Globular
proteins (e.g., enzymes, some hormones, antibodies, hemoglobin)
perform special functional roles for the cell (e.g., catalysis,
Proteins are denatured by extremes of temperature or pH.
Denatured globular proteins are unable to perform their usual
Molecular chaperones assist in folding proteins into their
functional 3-D shape. Tey are synthesized in greater amounts
when cells are stressed by environmental factors.
Enzymes are biological catalysts. Tey increase the rate of
chemical reactions by decreasing the amount of activation
energy needed. Tey do this by combining with the reactants and
holding them in the proper position to interact. Many enzymes
require cofactors to function.
Nucleic Acids (DNA and RNA)
Nucleic acids include deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA). Te structural unit of nucleic acids is
the nucleotide, which consists of a nitrogenous base (adenine,
guanine, cytosine, thymine, or uracil), a sugar (ribose or
deoxyribose), and a phosphate group.
DNA is a double-stranded helix. It contains deoxyribose and
the bases A, G, C, and ±. DNA speciﬁes protein structure and
replicates itself exactly before cell division.
RNA is single stranded. It contains ribose and the bases A, G,
C, and U. RNAs involved in carrying out DNA’s instructions for
protein synthesis include messenger, ribosomal, and transfer
Adenosine Triphosphate (ATP)
A±P is the universal energy compound of body cells. Some of
the energy liberated by the breakdown of glucose and other food
fuels is captured in the bonds of A±P molecules and transferred
via coupled reactions to energy-consuming reactions.
Fluid, Electrolyte and Acid/Base Balance; Topic: Acid Base
Homeostasis, pp. 1–12, 16, 17.
Bases are proton acceptors. Te most common inorganic bases
are the hydroxides; bicarbonate ion and ammonia are important
bases in the body.
pH is a measure of hydrogen ion concentration of a solution (in
moles per liter). A pH of 7 is neutral; a higher pH is alkaline, and
a lower pH is acidic. Normal blood pH is 7.35–7.45. Buﬀers help
to prevent excessive changes in the pH of body ﬂuids.
Fluid, Electrolyte and Acid/Base Balance; Topic: Introduction to
Body Fluids, pp. 1–8.
Organic compounds contain carbon. Tose found in the body
include carbohydrates, lipids, proteins, and nucleic acids, all of
which are synthesized by dehydration synthesis and digested by
hydrolysis. All of these biological molecules contain C, H, and O.
Proteins and nucleic acids also contain N.
Carbohydrate building blocks are monosaccharides, the most
important of which are hexoses (glucose, fructose, galactose) and
pentoses (ribose, deoxyribose).
Disaccharides (sucrose, lactose, maltose) and polysaccharides
(starch, glycogen) are composed of linked monosaccharide units.
Carbohydrates, particularly glucose, are the major energy fuel
for forming A±P. Excess carbohydrates are stored as glycogen or
converted to fat for storage.
Lipids dissolve in fats or organic solvents, but not in water.
±riglycerides are composed of fatty acid chains and glycerol. Tey
are found chieﬂy in fatty tissue where they provide insulation
and reserve body fuel. Unsaturated fatty acid chains produce oils.
Saturated fatty acids produce solid fats typical of animal fats.
Phospholipids are modiﬁed phosphorus-containing triglycerides
that have polar and nonpolar portions. Tey are found in all
Te steroid cholesterol is found in cell membranes and is the
basis of steroid hormones, bile salts, and vitamin D.
Te unit of proteins is the amino acid, and 20 common amino
acids are found in the body.
(Some questions have more than one correct answer. Select the best
answer or answers from the choices given.)
Which of the following forms of energy is the stimulus for vision?
All of the following are examples of the four major elements
contributing to body mass except
Te mass number of an atom is
equal to the number of
protons it contains,
the sum of its protons and neutrons,
the sum of all of its subatomic particles,
the average of the
mass numbers of all of its isotopes.
A deﬁciency in this element can be expected to reduce the
hemoglobin content of blood:
Which set of terms best describes a proton?
massless, in the orbital;
positive charge, 1 amu, in the nucleus;
uncharged, 1 amu, in the nucleus.
Te subatomic particles responsible for the chemical behavior of
In the body, carbohydrates are stored in the form of