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The hereditary material in a cell is coded in the sequence of the heterocyclic amines of DNA. There are normally 46 strands of DNA called chromosomes in human cells. Specific regions, called genes, on each chromosome contain the hereditary information which distinguishes individuals from each other. The genes also contain the coded information required for the synthesis of proteins and enzymes needed for the normal functions of the cells. Bacterial cells may have 1000 genes, while the human cell contains more than a million genes. A single E. coli (bacteria) chromosome of double helical DNA consists of 3.4 million base pairs.
Prior to cell division, the DNA material in the original cell must be duplicated so that after cell division, each new cell contains the full amount of DNA material. The process of DNA duplication is usually called replication.