Overview
- Know and be familiar with the specific roles of the six important elements in living organisms. These are:
- Carbon
- Hydrogen
- Nitrogen
- Oxygen
- Phosphorous
- Sulfur
- Carbon
- 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
- Hydrogen (partially charged and ion)
Introduction
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).
Item | Structural Role | Functional Role |
|---|---|---|
Carbon (C) | Molecular “backbone” (four bonds) | Multiple functional groups. |
Hydrogen (H) | “Accessory” structural (one bond) | Transferring from one molecule to another or in solution as H+. |
Nitrogen (N) | Forms specialized functional entities such as amines and ammonia molecules (three or four bonds) | Specialized bonds (amino acids/proteins), hydrogen bonding in DNA/RNA, and special functions. |
Oxygen (O) | Specialized functional structures (two bonds) | Often develops partial charge involved in hydrogen bonding, component of high-energy phosphate bonds for biological energy storage. |
Phosphate (P) | High energy and special molecular structures (four to six bonds) | Biological energy storage, essential component of DNA and RNA structure and function. |
Sulfur (S) | Strong structural bonds (two bonds) | Reversible bonding of important structural biological molecules. |
The Six Organic Elements (C, H, N, O, P, and S)
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 molecule to another or be by itself as H+ (see next section). H forms one bond with another element. H is found in most biological molecules.
Involved in many energy transfers and specialized structures. N usually forms three or four bonds with other elements. N is important in biological molecules including amino acids/proteins, complex carbohydrates, and lipids and in nucleic acids.
