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  • ▄ Know and be familiar with the specific roles of the six important elements in living organisms. These are:

    • Carbon

    • Hydrogen

    • Nitrogen

    • Oxygen

    • Phosphorous

    • Sulfur

  • ▄ Be familiar with the important functional groups that are formed by the six basic elements and understand their general structural and functional roles in biology and medicine.

    • Hydrogen (partially charged and ion)

    • Hydroxyl group

    • Carboxylic acid group

    • Amine group

    • Phosphate group

    • Sulfur-sulfur bond

    • Aldehyde group

    • Ketone group


Although there are over 100 elements known, only a few are regularly seen in nature. In fact, less than a third of the elements found on earth are found in some life form, with only six elements seen in all living organisms. These elements are carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S). These six “biological” elements can be remembered as C—H—N—O—P—S that sounds like “chin-ups.” These six elements can bond with themselves (e.g., C—C and O—O) and with each other (C—H, O—H, and C—N). Special bonding patterns lead to charged H atoms as well as hydroxyl, carboxyl, amine, high-energy phosphorus, and strong sulfide-bonded groups. These molecules serve structural and functional roles as well as specialized roles in very specific biological actions and reactions for functions in the human body (Table 1).


The Six Basic Elements of Life



Main structural element of all living tissue, C usually forms four bonds with other elements. C—C bonds (e.g., sugar or fat molecules) contain energy used in metabolism. C is found in almost all biological molecules.


Hydrogen can exist with both a partial charge and a full ionic charge, making its roles both varied and versatile. H is an important structural element but is often also seen in accessory roles, helping to form important functional groups and molecular structures. Functionally, H can transfer from one ...

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