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Name: Debbie Howard
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Question:
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!



Replies:
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.

--Brian



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