How your cell makes very important proteins - Part 4

Mutations in other body cells only cause trouble when they cause cancer or related diseases. Mutagens are chemical or physical agents that interact with DNA to cause mutations. Physical agents include high-energy radiation like X-rays and ultraviolet light. Chemical mutagens fall into several categories. Chemicals that are base analogues that may be substituted into DNA, but they pair incorrectly during DNA replication. Interference with DNA replication by inserting into DNA and distorting the double helix. Chemical changes in bases that change their pairing properties. Tests are often used as a preliminary screen of chemicals to identify those that may cause cancer. Most carcinogens are mutagenic and most mutagens are carcinogenic. Scientists have recognized a number of tumor viruses that cause cancer in various animals, including humans. About 15% of human cancers are caused by viral infections that disrupt normal control of cell division. All tumor viruses transform cells into cancer cells through the integration of viral nucleic acid into host cell DNA. Point mutations involve alterations in the structure or location of a single gene. Generally, only one or a few base pairs are involved. Point mutations can signficantly affect protein structure and function. Point mutations may be caused by physical damage to the DNA from radiation or chemicals, or may occur spontaneously. Point mutations are often caused by mutagens. The change of a single nucleotide in the DNA’s template strand leads to the production of an abnormal protein. Point mutations within a gene can be divided into two general categories. Base-pair substitutions - is the replacement of one nucleotide and its partner with another pair of nucleotides. Base-pair insertions or deletions - are additions or losses of nucleotide pairs in a gene.