Name: Debbie Howard
Excuse my ignorance - I am a librarian trying to assist a patron with his
question. The question is as follows - Can anyone out there explain what criteria
classifies molecules into the following categories: RNA, proteins, hormones, enzymes,
neuro transmitters, etc? If molecules function in a manner that fits more than one
criteria of different categories, does this mean these molecules can be doubly labeled?
For instance, is RNA both a protein and an enzyme? What is the relationship between
categories - for instance - are hormones enzymes but not all enzymes are hormones?
Where can I find molecule illustrations that depict the criteria for categories and
demonstrate molecule interactive functions?
Here's hoping this question is appropriate and answerable. Thanks!
Good question. Terms in biology are sometimes confusing. The molecules you listed
can be classified in at least two ways - chemically and functionally. DNA and RNA
belong to a chemical group called nucleic acids. They are made up of units known as
nucleotides, each of which contains a sugar, a phosphate group, and a nitrogenous base
(a certain molecular ring structure containing nitrogen). Proteins are another chemical
group and have a different structure altogether. They are composed of amino acids.
The terms protein and nucleic acid refer to chemical structure. Terms such as hormone,
enzyme, and neurotransmitter refer to functions. Enzymes are biological molecules that
catalyze chemical reactions. Most known enzymes are proteins, although a few RNA
molecules are known to have enzymatic activity. Hormones are molecules produced
in one part of an organism that function in another part. They usually
accomplish communication between different parts of the organism. Many hormones
are proteins, but many belong to other chemical groups such as steroids. In plants,
a very simple molecule, ethylene, actually functions as a hormone. Nucleic acids are
not known to function as hormones. Neurotransmitters are similar to hormones, but
function over shorter distances, usually between adjacent nerve cells. So more than one
label can apply to a particular molecule. A molecule can be both a protein and an
enzyme. RNA is not a protein, but an RNA molecule might be an enzyme. Hormones are not
the same as enzymes. A high school level biology textbook should have good illustrations
of all of these molecules and should show how they interact.
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Update: June 2012