RNA polymerase IIIIn eukaryote cells, RNA polymerase III (also called Pol III) is a protein that transcribes DNA to synthesize 5S ribosomal RNA, tRNA and other small RNAs. The genes transcribed by RNA Pol III fall in the category of "housekeeping" genes whose expression is required in all cell types and most environmental conditions. Therefore, the regulation of Pol III transcription is primarily tied to the regulation of cell growth and the cell cycle, and thus requires fewer regulatory proteins than RNA polymerase II.
Natural selectionNatural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which is intentional, whereas natural selection is not. Variation exists within all populations of organisms. This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations.
RNA polymerase IIRNA polymerase II (RNAP II and Pol II) is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription.
Divergent evolutionDivergent evolution or divergent selection is the accumulation of differences between closely related populations within a species, sometimes leading to speciation. Divergent evolution is typically exhibited when two populations become separated by a geographic barrier (such as in allopatric or peripatric speciation) and experience different selective pressures that drive adaptations to their new environment. After many generations and continual evolution, the populations become less able to interbreed with one another.
Kin selectionKin selection is a process whereby natural selection favours a trait due to its positive effects on the reproductive success of an organism's relatives, even when at a cost to the organism's own survival and reproduction. Kin selection can lead to the evolution of altruistic behaviour. Kin selection is related to the concept of inclusive fitness, which combines the number of offspring produced with the number an individual can ensure the production of by supporting others (weighted by the relatedness between individuals).
Transcription (biology)Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules called non-coding RNAs (ncRNAs). mRNA comprises only 1–3% of total RNA samples. Less than 2% of the human genome can be transcribed into mRNA (Human genome#Coding vs. noncoding DNA), while at least 80% of mammalian genomic DNA can be actively transcribed (in one or more types of cells), with the majority of this 80% considered to be ncRNA.
Adaptive immune systemThe adaptive immune system, also known as the acquired immune system, or specific immune system is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates (the other being the innate immune system). Like the innate system, the adaptive immune system includes both humoral immunity components and cell-mediated immunity components and destroys invading pathogens.
Convergent evolutionConvergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. The cladistic term for the same phenomenon is homoplasy. The recurrent evolution of flight is a classic example, as flying insects, birds, pterosaurs, and bats have independently evolved the useful capacity of flight.
Immune systemThe immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli.
RNA polymerase IRNA polymerase 1 (also known as Pol I) is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA (but not 5S rRNA, which is synthesized by RNA polymerase III), a type of RNA that accounts for over 50% of the total RNA synthesized in a cell. Pol I is a 590 kDa enzyme that consists of 14 protein subunits (polypeptides), and its crystal structure in the yeast Saccharomyces cerevisiae was solved at 2.8Å resolution in 2013. Twelve of its subunits have identical or related counterparts in RNA polymerase II (Pol II) and RNA polymerase III (Pol III).
