什麼是噬菌體
一類傳染細菌的複合病毒。發現於20世紀初,發現後不久即開始用來治療人類的腺鼠疫、霍亂等細菌疾病,但並不成功。1940年代隨著抗生素的出現被放棄。1990年代隨著抗藥細菌的興起,噬菌體的治療潛力再度獲得重視。噬菌體有成千上萬種,每一種可能只能侵染一類或幾類細菌。噬菌體的核心基因物質可能是核糖核酸(RNA)或去氧核糖核酸(DNA)。在噬菌體侵染宿主細胞時,這種裂解型噬體或毒性噬體會藉由裂解(迸裂)宿主細胞而釋放出複製的濾過性病毒粒子。其他種類(稱潛溶性噬體或溫和性噬體)會將核酸植入宿主的染色體內,以在細胞分裂中複製。在此期間,噬菌體是無毒性的。這種濾過性染色體組以後會變得活躍,開始產生濾過性病毒粒子,破壞宿主細胞。赫爾希和蔡斯(M. Chase)在1952年把噬菌體用於一項著名的實驗中,這個實驗支援了DNA是基因物質的理論。由於噬菌體染色體組很小,而且很多都能在實驗室製備,因此它們是分子生物學家最喜歡用的研究工具。對噬體的研究可幫助闡明基因的重組、核酸複製以及蛋白質合成。
bacteriophage
Any of a group of usually complex viruses that infect bacteria. Discovered in the early 20th century, bacteriophages were used to treat human bacterial diseases such as bubonic plague and cholera, but were not successful; they were abandoned with the advent of antibiotics in the 1940s. The rise of drug-resistant bacteria in the 1990s focused renewed attention on the therapeutic potential of bacteriophages. Thousands of varieties exist, each of which may infect only one or a few types of bacteria. The core of a bacteriophage's genetic material may be either DNA or RNA. On infecting a host cell, bacteriophages known as lytic or virulent phages release replicated viral particles by lysing (bursting) the host cell. Other types, known as lysogenic or temperate, integrate their nucleic acid into the host's chromosome to be replicated during cell division. During this time they are not virulent. The viral genome may later become active, initiating production of viral particles and destruction of the host cell. A. D. Hershey and Martha Chase used a bacteriophage in a famous 1952 experiment that supported the theory that DNA is the genetic material. Because bacteriophage genomes are small and because large quantities can be prepared in the laboratory, they are a favorite research tool of molecular biologists. Studies of phages have helped illuminate genetic recombination, nucleic-acid replication, and protein synthesis.
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什麼是電子計算機X射線斷層成像
一種醫學影像診斷技術。用X射線對人體投射,經檢測器測定透射後的放射量,通過電子計算機處理,重建出人體斷層影象,並作出診斷。簡史1895年倫琴發現X射線後,X射線立即被應用於臨床診斷。為了克服影像重疊的缺點,從1914年起,先後有人採用X射線管與膠片作同步反向運動的方...
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什麼是石膏
常用清熱瀉火藥。始載於《神農本草經》。別名細理石、寒水石、軟石膏。為硫酸鹽類礦物硬石膏族石膏。石膏有軟、硬石膏兩種,中醫中的石膏為軟石膏。產地和性狀石膏多產於海灣鹽湖和內陸湖泊形成的沉積岩中,常與石灰岩、黏土、岩鹽伴生。中國的主產地是湖北、安徽...
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什麼是皮內針
用於淺刺埋針的小型針具。因針僅刺入皮內,故名。按其形狀可分為顆粒式、環式、撳釘式三種:(1)顆粒式。形似毫針,長7毫米或9毫米,針尾為金屬顆粒,常用直徑為0.22毫米或0.26毫米的金、銀或不鏽鋼絲製成。(2)環式。針尾呈環狀,長7毫米或9毫米,常用直徑0.26毫米的不鏽鋼絲製成...
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什麼是熟地黃
常用補血藥。別名熟地。始載於《本草圖經》。為玄蔘科多年生草本植物地黃Rehmanniaglutinosa根經加黃酒拌蒸至內外色黑而油潤,或直接蒸至黑潤而成(圖1)。因其色黃,質量下沉,蒸熟晒乾入藥,故名。產地和性狀中國大部地區均有生產,主產於河南孟縣、溫縣、武陟、博愛等...