A gene regulatory network or genetic regulatory network is a collection of DNA segments in a cell which interact with each other and with other substances in the cell, thereby governing the rates at which genes in the network are transcribed into mRNA. In general, each mRNA molecule goes on to make a specific protein . In some cases this protein will be structural, and will accumulate at the cell-wall or within the cell to give it particular structural properties. In other cases the protein will be an enzyme; a micro-machine that catalyses a certain reaction, such as the breakdown of a food source or toxin. Some proteins though serve only to activate other genes, and these are the transcription factors that are the main players in regulatory networks or cascades. By binding to the promoter region at the start of other genes they turn them on, initiating the production of another protein, and so on. Some transcription factors are inhibitory.
In single-celled organisms regulatory networks respond to the external environment, optimising the cell at a given time for survival in this environment. Thus a yeast cell, finding itself in a sugar solution, will turn on genes to make enzymes that process the sugar to alcohol. This process, which we associate with wine-making, is how the yeast cell makes its living, gaining energy to multiply, which under normal circumstances would enhance its survival prospects.
In multicellular animals the same principle has been put in the service of gene cascades that control body-shape. Each time a cell divides, two cells result which, although they contain the same genome in full, can differ in which genes are turned on and making proteins. Sometimes a self-sustaining feedback loop ensures that a cell maintains its identity and passes it on. Less understood is the mechanism of epigenetics by which chromatin modification may provide cellular memory by blocking or allowing transcription. A major feature of multicellular animals is the use of morphogen gradients, which in effect provide a positioning system that tells a cell where in the body it is, and hence what sort of cell to become. A gene that is turned on in one cell may make a product that leaves the cell and diffuses through adjacent cells, entering them and turning on genes only when it is present above a certain threshold level. These cells are thus induced into a new fate, and may even generate other morphogens that signal back to the original cell. Over longer distances morphogens may use the active process of signal transduction. Such signalling controls embryogenesis, the building of a body plan from scratch through a series of sequential steps. They also control maintain adult bodies through feedback processes, and the loss of such feedback because of a mutation can be responsible for the cell proliferation that is seen in cancer. In parallel with this process of building structure, the gene cascade turns on genes that make structural proteins that give each cell the physical properties it needs. It has been suggested that, because biological molecular interactions are intrinsically stochastic, gene networks are the result of cellular processes and not their cause. However, recent experimental evidence has favored the attractor view of cell fates.
上一篇: SAT阅读方法与原则
体坛英语资讯:Maradona wants to continue coaching Argentine national team
体坛英语资讯:Vitoria beat Atletico-MG 3-2
体坛英语资讯:England to pull out of bidding for 2022 World Cup
体坛英语资讯:Cleveland Cavaliers End Longest Losing Streak in NBA History
体坛英语资讯:Gremio beat Avai 3-0
体坛英语资讯:Australias Melzer wins ITF Men s circuit final in Kampala
体坛英语资讯:Chinese volleyball coach views tough group battle at mens worlds
体坛英语资讯:Indian trade minister lashes out at critics of Commonwealth Games
体坛英语资讯:Russians grab last two golds at rhythmic gymnastics worlds
体坛英语资讯:Chile not to complain with U.S. matchup draw in Davis Cup
体坛英语资讯:Real Sociedad signs Norwegian defender Vadim Demidov
体坛英语资讯:Mourinho ends Portugal controversy
体坛英语资讯:Cielo loses to fellow Brazilian Santos in 50m butterfly
体坛英语资讯:Ujfalusi receives two game ban for Messi challenge
体坛英语资讯:Villa goal gives Barcelona win while Atletico draws in Valencia
体坛英语资讯:Guardiola angry at Messi injury
体坛英语资讯:Martirosyan of Armenia crowns double at weightlifting worlds
体坛英语资讯:Real beat Espanyol while Athletic, Espanyol also win in Spain
体坛英语资讯:Guardiola celebrates Messis 10th anniversary
体坛英语资讯:Hosts China lead title contention in womens volleyball Asian Cup
体坛英语资讯:Brazils Cielo tops 12-year record in 100m freestyle
体坛英语资讯:Andrade hired as head coach of Brasiliense
体坛英语资讯:Arsenal, Chelsea keep perfect record; Bayern, Real also win again
体坛英语资讯:Boavista eliminate Fluminense from state finals
体坛英语资讯:给力芬悼念亡友 继续全明星征程
体坛英语资讯:Mourinho upset as Real Madrid rejects his Portugal hopes
体坛英语资讯:Arsenal suffer bitter draw at Sunderland
体坛英语资讯:False ceiling collapses at Delhi Games venue
体坛英语资讯:7th Regional Special Olympics to open in Syria
体坛英语资讯:Messi to miss 3-6 weeks with ankle injury