第四章——病毒 非细胞生物的种类: （真）病毒(virus)：至少含有核酸和蛋白质两种 组分 类病毒(viroid)：只含单独具侵染性的RNA组分 亚病毒 拟病毒(virusoid)：只含不具单独侵染性的RNA组分 垣病毒(prion)：只含蛋白质一种组分 ★This chapter focuses on the characteristics of the bacterial viruses, or bacteriophages. It begins with their classification and then details the infectious cycle of those DNA viruses that cause destruction (lysis) of host cells. RNA phages are discussed briefly, and the chapter concludes with information about phages that can integrate their DNA into the host chromosome and thereby set up a stable residence within the host cell. These phages are called temperate phages, and the process is referred to as lysogeny. ★CHAPTER OBJECTIVES After reading this chapter you should be able to: o describe the four phases of the viral life cycle o discuss the differences between DNA phages and RNA phages in terms of their life cycles and their interactions with their hosts o discuss the establishment and maintenance of lysogeny by temperate phages

第一节 概述

一、人类对病毒的发现和认识过程 1892：俄国 伊万诺夫斯基 首次发现烟草花叶病毒的感染因子能通过细菌过滤器。 1892：俄国 伊万诺夫斯基 首次发现烟草花叶病毒的感染因子能通过细菌过滤器。 1898：荷兰 贝哲林克 证实该致病因子可以被乙醇从悬液中沉淀下来而不失去其感染性但用培养细菌的方法培养不出来；给这样的病原体起名叫virus。 1935：美国 斯坛莱 从烟草花叶病病叶中提取出了病毒结晶，又证实了结晶中含核酸和蛋白质两种成分，而只有核酸具感染和复制能力，并因此而或诺贝尔奖。 1952：Hershey和Chase证实噬菌体的遗传物质仅仅是DNA,开创了病毒分子生物学。 1971后：陆续发现了各种亚病毒——类病毒、元病毒、和拟病毒。

二、定义和特点 形体极其微小，必须在电子显微镜下才能观察，一般都可通过细菌滤器； 没有细胞构造，故也称分子生物； 其主要成分仅是核酸和蛋白质两种； 每一种病毒只含有一种核酸，不是DNA就是RNA； 既无产能酶系也无蛋白质合成系统； 在宿主细胞协助下，通过核酸的复制和核酸蛋白装配的形式进行增殖，不存在个体生长和二均等分裂等细胞繁殖方式； 在宿主的活细胞内营专性寄生； 在离体条件下，以无生命的化学大分子状态存在，并可形成结晶； 对一般抗生素不敏感，但对干扰素敏感。

三、宿主范围（分布）及重要性 几乎所有的生物都可以 感染相应的病毒。根据宿主可以分三类： 动物病毒 植物病毒 细菌病毒（或称噬菌体）

第二节 病毒的大小、形态、构造和组分 Size and Shapes of Viruses 第二节　病毒的大小、形态、构造和组分 Size and Shapes of Viruses 1. Size (see Fig. 1A, Fig. 1B, and Fig. 1C) Viruses are usually much smaller than bacteria and are submicroscopic (def). Most range in size from 5 to 300 nanometers (nm) (def), although some Paramyxoviruses can be up to 14,000nm long. For a comparison of the size of a virus, a bacterium, and a human cell, scroll down to how big is... on the CELL'S ALIVE web page. 2. Shapes (see Fig. 1A, Fig. 1B, and Fig. 1C) a. Helical viruses (def) consist of nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure (see Fig. 2A). b. Polyhedral viruses (def) consist of nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the form of an icosahedron (def); (see Fig. 2B and Fig. 1E). - Scanning electron micrograph of poliomyelitis viruses; courtesy of Dennis Kunkel's Microscopy. c. Enveloped viruses (def) consist of nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope (see Fig. 2C, Fig. 2D, Fig. 1F and Fig. 1H, and Fig. 3A). - Scanning electron micrograph of herpes simplex viruses; courtesy of Dennis Kunkel's Microscopy. d. Binal (complex) viruses (def) have neither helical nor polyhedral forms, are pleomorphic (irregular shaped), or have complex structures (see Fig. 2E). - Scanning electron micrograph of the bacteriophage coliphage T4; courtesy of Dennis Kunkel's Microscopy.

一、大小 侧定大小的单位是纳米（10－9)，多数病毒的直径在100nm以下； 绝大多数病毒是能通过细菌滤器； 须用电镜才能观察到其具体形态和大小. 1. Size (see Fig. 1A, Fig. 1B, and Fig. 1C) Viruses are usually much smaller than bacteria and are submicroscopic (def). Most range in size from 5 to 300 nanometers (nm) (def), although some Paramyxoviruses can be up to 14,000nm long. For a comparison of the size of a virus, a bacterium, and a human cell, scroll down to how big is... on the CELL'S ALIVE web page.

二、形态

Fig. 1A: Sizes and Shapes of Viruses (Animal RNA Viruses) 2. Shapes (see Fig. 1A, Fig. 1B, and Fig. 1C) a. Helical viruses (def) consist of nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure (see Fig. 2A). b. Polyhedral viruses (def) consist of nucleic acid surrounded by a polyhedral (many-sided) shell or capsid, usually in the form of an icosahedron (def); (see Fig. 2B and Fig. 1E). - Scanning electron micrograph of poliomyelitis viruses; courtesy of Dennis Kunkel's Microscopy. c. Enveloped viruses (def) consist of nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope (see Fig. 2C, Fig. 2D, Fig. 1F and Fig. 1H, and Fig. 3A). - Scanning electron micrograph of herpes simplex viruses; courtesy of Dennis Kunkel's Microscopy. d. Binal (complex) viruses (def) have neither helical nor polyhedral forms, are pleomorphic (irregular shaped), or have complex structures (see Fig. 2E). - Scanning electron micrograph of the bacteriophage coliphage T4; courtesy of Dennis Kunkel's Microscopy.

Fig. 1B: Sizes and Shapes of Viruses (Animal DNA Viruses)

Transmission Electron Micrograph of Herpes simplex Viruses

Tobacco mosaic virus (TMV)