Chemical elements are the building blocks of the several molecules found in biological systems. These elements combine with each other through covalent linkages in specific proportions to form molecules that perform several body functions. Although there are more than 30 elements present in the body, the ones that are most abundant include carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur.
Carbon, Hydrogen and Oxygen
All organic biomolecules contain the elements carbon in combination with hydrogen and oxygen. This forms the carbon skeleton that is the basic structure of almost all molecules found within cells. Carbohydrates, proteins and fats all contain the carbon skeleton. Other biological entities -- such as the nucleic acids, enzymes, coenzymes, porphyrins -- also contain this carbon skeleton to which other elements are attached.
The element nitrogen is a major component of several biological molecules. The most important of these are proteins. Proteins are polymers of amino acids in which the nitrogen-containing amino group is attached to a carbon skeleton. Enzymes, which are all protein in nature, also contain nitrogen. Deoxyribonucleic acid and ribonucleic acid contain purine and pyrimidine molecules that are nitrogen-containing bases. Some hormones, such as insulin and oxytocin, are peptide in nature and therefore contain nitrogen.
Phosphorus is a vital element and often exists in the biological system in the form of phosphate. A major proportion of the phosphorus is present in bone as the salt of calcium known as hydroxyapatite. In combination with lipids, phosphorus is present in phospholipids, such as phosphatidyl choline, that is an important entity in the cell membrane. Phosphorus is also present in the high energy compounds, such as creatine phosphate and adenosine tri phosphate (ATP). All metabolic reactions in the body either utilize or produce ATP. The nucleic acids also contain phosphate as part of their structure.
A few amino acids, such as methionine, cysteine and cystine, contain sulfur. These amino acids are involved in several important metabolic reactions, such as cellular respiration. Sulfur is also present in the protein called keratin found in the hair, skin and nails, which lends strength and hardness to these structures. Connective tissue in human bodies contains collagen that requires sulfur for its formation. The anticoagulant heparin and bile acid component taurine also contain sulfur.
Several other elements are a vital component of biological systems. An important one is calcium, which is found in bones and teeth and cellular fluids. Magnesium in cell membranes, chromosomes and bones, and iron, which is present in the respiratory pigment called hemoglobin, are other well-known examples.