White blood cells called B cells produce proteins that can be used for the treatment of certain illnesses. However, these B cells do not live for very long on their own. To keep the B cells growing for a long time in laboratories, scientists fuse the B cells with cancer cells (fused B-cancer cells) that do grow for a very long time. The particular cancer cells used for the fusion are treated with chemicals that make them unable to produce the nitrogenous bases adenine and guanine, but the B cells with which they are fused do produce these nitrogenous bases. The scientists grow the large fused B-cancer cells in a growth medium that contains necessary nutrients for the cells and includes a source of carbon.

Without carbon, there would be no life on earth. Carbon molecules have the ability to form bonds that are stable with a vast number of molecules. It can also form bonds with itself. The proteins, amino acids, DNA, RNA, lipids all contain carbon molecules. Hence, it serves as the basic compound for making molecules of life. In the growth culture media, Carbon is added in the form of carbohydrates like glucose or glutamine as it provides main source of energy.