science to clinical, and vice versa. Biochemical thinking is very step-
wise, for example, the relationship among DNA, ribonucleic acid
(RNA), proteins, and clinical findings. Since the genomic information
(DNA) codes for proteins that affect physiologic or pathologic
changes, it is of fundamental importance that the student becomes very
comfortable thinking about these relationships:
Forward: DNA ^ proteins ^ Clinical Manifestations
Backward: Clinical Findings ^ proteins’ effects
What hormone-receptor interaction is likely?
is a substance, usually a peptide or steroid, produced by
one tissue and conveyed by the bloodstream to another part of the body
to effect physiological activity, such as growth or metabolism. A
is a cellular structure that mediates between a chemical agent
(hormone) and the physiologic response. The way that the hormone
causes its effect is vital to understand, because many diseases occur as
a result of abnormal hormone production, abnormal hormone receptor
interaction, or abnormal cellular response to the hormone-receptor
complex. For example, diabetes mellitus is manifest clinically by high
blood glucose levels. However, in type I diabetes (usually juvenile
onset), the etiology is insufficient insulin secreted by the pancreas.
(Insulin acts to put serum glucose into cells or store it as glycogen.) In
contrast, the mechanism in type II diabetes (usually adult onset) is a
defect of the insulin receptor messenger; in fact, the insulin levels in
these individuals are usually higher than normal. Understanding the
difference between the two mechanisms allows the scientist to
approach individualized therapy, and it allows the clinician to under-
stand the differences in these patients, such as the reason that type I
diabetics are much more prone to diabetic ketoacidosis (because of
insulin deficiency).
How does the presence or absence of enzyme activity affect the bio-
chemical (molecular) conditions, and how does that in turn affect
patient symptoms?
Enzymes are proteins that act as catalysts, speeding the rate at which
biochemical reactions proceed but not altering the direction or nature
of the reactions. The presence or absence of these important substances
affects the biochemical conditions, which then influence the other
physiologic processes in the body. Enzyme deficiencies are often
inherited as autosomal recessive conditions and may be passed from
parent to child. Clearly, when students begin to understand the role of
the enzyme and the chemical reaction that it governs, they begin to
understand the intricacies of the human biological processes.
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