DNA repair in the context of "Mutation (biology)"

In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis, or meiosis or other types of damage to DNA (such as pyrimidine dimers caused by exposure to ultraviolet radiation), which then may undergo error-prone repair (especially microhomology-mediated end joining), cause an error during other forms of repair, or cause an error during replication (translesion synthesis). Mutations may also result from substitution, insertion or deletion of segments of DNA due to mobile genetic elements.

Mutations may or may not produce detectable changes in the observable characteristics (phenotype) of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution, cancer, and the development of the immune system, including junctional diversity. Mutation is the ultimate source of all genetic variation, providing the raw material on which evolutionary forces such as natural selection can act.

In molecular biology, complementarity describes a relationship between two structures each following the lock-and-key principle. In nature complementarity is the base principle of DNA replication and transcription as it is a property shared between two DNA or RNA sequences, such that when they are aligned antiparallel to each other, the nucleotide bases at each position in the sequences will be complementary, much like looking in the mirror and seeing the reverse of things. This complementary base pairing allows cells to copy information from one generation to another and even find and repair damage to the information stored in the sequences.

The degree of complementarity between two nucleic acid strands may vary, from complete complementarity (each nucleotide is across from its opposite) to no complementarity (each nucleotide is not across from its opposite) and determines the stability of the sequences to be together. Furthermore, various DNA repair functions as well as regulatory functions are based on base pair complementarity. In biotechnology, the principle of base pair complementarity allows the generation of DNA hybrids between RNA and DNA, and opens the door to modern tools such as cDNA libraries.While most complementarity is seen between two separate strings of DNA or RNA, it is also possible for a sequence to have internal complementarity resulting in the sequence binding to itself in a folded configuration.

Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling.

Genes are the common factor of the qualities of most human-inherited traits. Study of human genetics can answer questions about human nature, can help understand diseases and the development of effective treatment and help us to understand the genetics of human life. This article describes only basic features of human genetics; for the genetics of disorders please see: medical genetics. For information on the genetics of DNA repair defects related to accelerated aging and/or increased risk of cancer please see: DNA repair-deficiency disorder.

Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) in a standard regimen. Chemotherapy may be given with a curative intent (which almost always involves combinations of drugs), or it may aim only to prolong life or to reduce symptoms (palliative chemotherapy). Chemotherapy is one of the major categories of the medical discipline specifically devoted to pharmacotherapy for cancer, which is called medical oncology.

The term chemotherapy now means the non-specific use of intracellular poisons to inhibit mitosis (cell division) or to induce DNA damage (so that DNA repair can augment chemotherapy). This meaning excludes the more-selective agents that block extracellular signals (signal transduction). Therapies with specific molecular or genetic targets, which inhibit growth-promoting signals from classic endocrine hormones (primarily estrogens for breast cancer and androgens for prostate cancer), are now called hormonal therapies. Other inhibitions of growth-signals, such as those associated with receptor tyrosine kinases, are targeted therapy.

DNA replication is the process by which a cell makes exact copies of its DNA. This process occurs in all organisms and is essential to biological inheritance, cell division, and repair of damaged tissues. DNA replication ensures that each of the newly divided daughter cells receives its own copy of each DNA molecule.

DNA most commonly occurs in double-stranded form, made up of two complementary strands held together by base pairing of the nucleotides comprising each strand. The two linear strands of a double-stranded DNA molecule typically twist together in the shape of a double helix. During replication, the two strands are separated, and each strand of the original DNA molecule then serves as a template for the production of a complementary counterpart strand, a process referred to as semiconservative replication. As a result, each replicated DNA molecule is composed of one original DNA strand as well as one newly synthesized strand. Cellular proofreading and error-checking mechanisms ensure near-perfect fidelity for DNA replication.

Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abnormal cell division. Cell division is a physiological process that occurs in almost all tissues and under a variety of circumstances. Normally, the balance between proliferation and programmed cell death, in the form of apoptosis, is maintained to ensure the integrity of tissues and organs. According to the prevailing accepted theory of carcinogenesis, the somatic mutation theory, mutations in DNA and epimutations that lead to cancer disrupt these orderly processes by interfering with the programming regulating the processes, upsetting the normal balance between proliferation and cell death. This results in uncontrolled cell division and the evolution of those cells by natural selection in the body. Only certain mutations lead to cancer whereas the majority of mutations do not.

Variants of inherited genes may predispose individuals to cancer. In addition, environmental factors such as carcinogens and radiation cause mutations that may contribute to the development of cancer. Finally random mistakes in normal DNA replication may result in cancer-causing mutations. A series of several mutations to certain classes of genes is usually required before a normal cell will transform into a cancer cell. Recent comprehensive patient-level classification and quantification of driver events in TCGA cohorts revealed that there are on average 12 driver events per tumor, of which 0.6 are point mutations in oncogenes, 1.5 are amplifications of oncogenes, 1.2 are point mutations in tumor suppressors, 2.1 are deletions of tumor suppressors, 1.5 are driver chromosome losses, 1 is a driver chromosome gain, 2 are driver chromosome arm losses, and 1.5 are driver chromosome arm gains. Mutations in genes that regulate cell division, apoptosis (cell death), and DNA repair may result in uncontrolled cell proliferation and cancer.

Gene duplication (or chromosomal duplication or gene amplification) is a mechanism through which new genetic material is generated during molecular evolution. It can be defined as any duplication of a region of DNA that contains a gene. Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.