《微生物学》课程教学课件（PPT讲稿）Chapter 6 Viruses

Chapter 6 viruses 6. 1 General Properties of Viruses 6.2 Structure of viruses 6.3 The cultivation of viruses 6. 4 General Features of Virus Reproduction 6. 5 one-step growth curve 6.6 Temperate Bacteriophages: Lysogeny and Lambda 6.7 viral classification 6.8 Overview of animal viruses 6.9 plant viruses 6.10 Viroids and Prions

6.1 General Properties of Viruses 6.2 Structure of viruses 6.3 The cultivation of viruses 6.4 General Features of Virus Reproduction 6.5 one-step growth curve 6.6 Temperate Bacteriophages: Lysogeny and Lambda 6.7 viral classification 6.8 Overview of Animal Viruses 6.9 plant viruses 6.10 Viroids and Prions Chapter 6 Viruses

TThe viruses Introduction and general characteristics Virus: simple, acellular entities consisting of one or more molecules of either DNA or RNa enclosed in a coat of protein. They are reproduced only within living cells and are obligately intracellular pa arasites The nucleic acid strands can be linear, closed cycle, or able to assume either shape A virus particle containing nucleic acid surrounded by protein and other macromolecular components Is called virion Viruses have a heavy dependence on host-cell structural and metabolic components Viruses can confer important new properties on their host cell

The Viruses Introduction and general characteristics • Virus : simple, acellular entities consisting of one or more molecules of either DNA or RNA enclosed in a coat of protein. They are reproduced only within living cells and are obligately intracellular parasites • The nucleic acid strands can be linear, closed cycle, or able to assume either shape • A virus particle containing nucleic acid surrounded by protein and other macromolecular components is called virion. • Viruses have a heavy dependence on host-cell structural and metabolic components. • Viruses can confer important new properties on their host cell

6.1 General Properties of viruses Viruses differ from living cells in at least three ways: (1) their simple, acellular organization (2)the absence of both dna and rna in the same vIrion, 3)their inability to reproduce independently of cells and carry out cell division as prokaryotes and eukaryotes do

(1) their simple, acellular organization (2) the absence of both DNA and RNA in the same virion, (3) their inability to reproduce independently of cells and carry out cell division as prokaryotes and eukaryotes do. Viruses differ from living cells in at least three ways: 6.1 General Properties of Viruses

Viruses can exist in two phases extracellular and intracellular The extracellular phase. posses few if any enzymes and can not reproduce independently of living cells In the intracellular phase, viruses exist primarily as replicating nucleic acids that induce host metabolism to synthesize virion components; eventually complete virus particles or virions are released

The extracellular phase, posses few if any enzymes and can not reproduce independently of living cells. In the intracellular phase, viruses exist primarily as replicating nucleic acids that induce host metabolism to synthesize virion components; eventually complete virus particles or virions are released. extracellular and intracellular Viruses can exist in two phases

Hosts and size Three main classes -animal viruses, bacterial viruses (bacteriophages), and plant viruses. The particular host range of a virus is determined by the virus's requirements for its specific attachment to the host cell and the availability within the potential host of cellular factors required for viral multiplication

Hosts and size Three main classes - animal viruses, bacterial viruses (bacteriophages), and plant viruses. The particular host range of a virus is determined by the virus's requirements for its specific attachment to the host cell and the availability within the potential host of cellular factors required for viral multiplication

Si oze Viruses vary considerably in size. Although most are quite a bit smaller than bacteria, some of the larger viruses(such as the smallpox virus) are about the same size as some very small bacteria(such as the mycoplasmas, rickettsia, and chlamydia) Viruses range from 20 to 300 nm in diameter

Viruses vary considerably in size. Although most are quite a bit smaller than bacteria, some of the larger viruses (such as the smallpox virus) are about the same size as some very small bacteria (such as the mycoplasmas, rickettsias, and chlamydias). Size Viruses range from 20 to 300 nm in diameter

The comparative sizes of several viruses and bacteria: 225mm Bacterashase M13 IcOrm in diamter e 2 nm Totacroesaic vius Racte Cameta (a bacterin ●3m L5I nn x 2mnm poliovirus Vaccinia virus 3at nm x 20 nm x Ico nm Lanterns ch rm tnick ia iterum

The comparative sizes of several viruses and bacteria:

Genome in virion RNA RNA一DN VIruses viruses Viruses SS DNA ds dNA SS RNA ds RNA SS RNA ds RNA (Retroviruses) Hepadnaviruses) Viral genomes. The genomes of viruses can be composed of either DNa or rna, and some use both as their genomic material at different stages in their life cycle However, only one type of nucleic acid is found in the virion of any particular type of virus. This can be single stranded(ss), double-stranded(ds), or in the case of the hepadnaviruses, partially double-stranded

Genome in virion Viral genomes. The genomes of viruses can be composed of either DNA or RNA, and some use both as their genomic material at different stages in their life cycle. However , only one type of nucleic acid is found in the virion of any particular type of virus. This can be single￾stranded (ss), double-stranded (ds), or in the case of the hepadnaviruses, partially double-stranded

6.2 Structure of viruses Most viruses are too small to be seen under light microscope. All viruses consists of an RNA or DNA core genome surrounded by a protein coat capsid. The combined viral genome and capsid is called the nucleocapsid capsid Envelope Capsomere Capsid Capsid capsomeres) Naked virus

• Most viruses are too small to be seen under light microscope. • All viruses consists of an RNA or DNA core genome surrounded by a protein coat capsid. • The combined viral genome and capsid is called the nucleocapsid. 6.2 Structure of viruses

The nucleic acid of a virus is surrounded by a protein coat called the capsid Each capsid is composed of protein subunits called capsomeres In some viruses, the capsid is covered by an envelope which usually consists of some combination of lipids proteins, and carbohydrates Depending on the virus envelopes may or may not be covered by spikes, which are carbohydrateprotein complexes that project from the surface of the envelope

The nucleic acid of a virus is surrounded by a protein coat called the capsid Each capsid is composed of protein subunits called capsomeres. In some viruses, the capsid is covered by an envelope, which usually consists of some combination of lipids, proteins, and carbohydrates. Depending on the virus, envelopes may or may not be covered by spikes, which are carbohydrateprotein complexes that project from the surface of the envelope