《微生物学》课件 Microbiology Chapter 2.2

1、living creaturecellullarNoncellullar: virusprokaryoteeucaryote2.3 virus2.3.1 The general characteristics of viruses2.3.1.1 Chemical compositionDNA or RNA, never both, single strand or double strandProteinsPhospholipidsSugar2.3.1.2 Noncellullar structureVirion: The structurally complete mature and in

2、fectious virus is called the virion. 2.3.1.3 Size and shapeViruses are so small that they can only be seen at magnifications provided by the electron microscope. They are 10100 times smaller than most bacteria, with an approximate size range of 20300nm. Thus they pass through the pores of filters过滤器

3、which do not permit the passage of most bacteria. Sizes and Shapes of Viruses (Animal RNA Viruses)Sizes and Shapes of Viruses (Animal DNA Viruses)乳头多瘤空泡病毒科 腺病毒科疱疹病毒The comparative sizes of several viruses and bacteria:Sizes and Shapes of Viruses (Bacteriophages)2.3.1.4 Obligate intracellular parasit

4、es Viruses are incapable of independent growth in artificial media. They can grow only in animal, plant cells or microorganisms, since viruses lack metabolic machinery of their own to generate energy or to synthesize proteins. They depend on the host cells to carry out these vital functions. 2.3.1.5

5、 Replication Viruses reproduce in the host cells by replication that is a process in which many copies are made of each viral component and are then assembled to produce progeny virus. During reproduction in the host cells viruses may cause diseases. TemperatureRadiation, ultraviolet radiation, - ra

6、diation Chemical reagents2.3.1.6 Environmental factors2.3.1.7 Definition of viruses Viruses are small and noncellular infectious entities whose genomes are a nucleic acid, either DNA or RNA; which reproduce only in living cells by replication.2.3.2 Bacteriophage Virus that infects bacteria is called

7、 Bacteriophage, Phage, or Bacterial virus.2.3.2.1 The shape of bacteriophage When lytic phages infect cells, the cells respond by producing large numbers of new viruses. That is, at the end of the incubation period the host cell bursts or lyses, releasing new phages to infect other host cells. This

8、process is called a lytic cycle. 裂解周期2.3.2.2 Lytic bacteriophage(毒/烈性噬菌体) Adsorption: during the Lytic Life Cycle of a Lytic Bacteriophage The bacteriophage binds to receptors on the bacterial cell wall.1) adsorption, attachment (吸附/附着) Attachment of phage to host cellAfter a chance collision betwee

9、n phage particles and bacteria, an attachment site on the virus attaches to a complementary 互补的receptor site on the bacterial cell. Penetration: during the Lytic Life Cycle of a Lytic Bacteriophage, the bacteriophage injects its genome into the bacteriums cytoplasm. 2) Penetration(侵入)During the proc

10、ess of penetration, the bacteriophages tail releases an enzyme, phage lysozyme, which breaks down a portion of the bacterial cell wall. then the bacteriophage injects its DNA (nucleic acid) into the bacterium. Early Replication: during the Lytic Life Cycle of a Lytic Bacteriophage, the bacteriophage

11、 genome replicates and bacteriophage components begin to be produced by way of the host bacteriums metabolic machinery. 3) nucleic acid replication(核酸复制)Biosynthesis of viral components:Any RNA transcribed in the cell is mRNA transcribed from phage DNA for biosynthesis of phage enzymes and capsid pr

12、otein. The host cells ribosomes, enzymes, and amino acids are used for translation Late Replication: during the Lytic Life Cycle of a Lytic Bacteriophage, The production of bacteriophage components and enzymes progresses. Maturation: during the Lytic Life Cycle of a Lytic Bacteriophage, the bacterio

13、phage components assemble. 4) Phage assembly (噬菌体装配)MaturationThe phage heads and tails are separately assembled from protein subunits, the head is packaged with phage DNA, and the tail is attached Release: during the Lytic Life Cycle of a Lytic Bacteriophage, A bacteriophage-coded enzyme breaks dow

14、n the peptidoglycan in the bacterial cell wall causing osmotic lysis. 5) Release(释放)Release: Lysozyme, whose code is provided by a phage gene, is synthesized within the cell. This enzyme causes a breakdown of the bacterial cell wall, and the newly produced bactedophages are released from the host ce

15、ll. The number of newly synthesized phage particles released from a single cell usually ranges from about 50 to 200. Animation of the Lytic Life Cycle of a Bacteriophageone-step growth curveThe viral nucleic acid is replicated in the host bacterial cells from one generation to another without any ce

16、ll lysis. However, temperate phages may spontaneously become virulent at some subsequent generation and lyse the host cells. 2.3.2.3 Temperate bacteriophage(温和噬菌体)Prophage Formation during the Lysogenic Life Cycle of a Temperate Bacteriophage The bacteriophage inserts its genome into the bacteriums

17、nucleoid to become a prophage. Animation of the Lysogenic Life Cycle of a Temperate Bacteriophage2.3.2.4 Bacteriophage and practiceIndustrial fermentationBiological controlGene engineering, phage2.3.3 SubvirusVirus that contains only nucleic acid or protein.2.3.3.1 ViroidSingle-stranded RNA 2.3.3.2

18、Prionsprotein infectionMad cow diseaseScrapie in sheep2.3.4 SARSSevere acute respiratory syndrome(严重急性呼吸道症候群) 2.3.5. HIVhuman immunodeficiency virus (人类免疫缺陷病毒)AIDS: acquired immune deficiency syndrome(获得性免疫缺陷综合症)2005年7月23日搜狐新闻禽流感病毒H5N1H5N1正在攻击健康的细胞蓝色部分就是H5N1禽流感病毒，红色部分是健康人体细胞H5N1 OIE International Spread of 一般情况下，禽流感病毒并不容易使人类发病。禽流感病毒属甲型流感病毒，甲型流感病毒根据其表面蛋白质的不同被分为H1到H15等15种亚型。Questions-11. What are the unique features of microorganism?2. List several applied areas of microbiology? Describe the importance of microorganisms in each of these applied fields