The function of each protein molecule depends on its specific sequence of amino acids. Most cells function best within a narrow range of temperature and acidity. Carbon, because of its small size and four available bonding electrons, can join to other carbon atoms in chains and rings to form large and complex molecules. The genetic information in DNA molecules provides instructions for assembling protein molecules. The code used is virtually the same for all life forms.
Genes are segments of DNA molecules, which contain instructions for specific proteins.
Gene mutation in a cell can result in uncontrolled cell division, called cancer. Exposure of cells to certain chemicals and radiation increases mutations and thus increases the chance of cancer. At times, environmental conditions are such that plants and marine organisms die faster than decomposers can recycle them back to the environment. Layers of energy-rich organic material have been gradually turned into great coal beds and oil pools by the pressure of the overlying earth. By burning these fossil fuels, people are passing most of the stored energy back into the environment as heat and releasing large amounts of carbon dioxide.