Lecture 9-3Essentials of Virology

Virus: Growth, quantification, replication and diversity

School of Life Science and Biotechnology,Shanghai Jiao Tong University

CHAPTER 9 inBROCK BIOLOGY OF MICROORGANISMS

9.11 Overview of Animal Viruses

p.250 section 9.12

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9.11.1 Differences between prokaryotes and eukaryotes that affect virus multiplication

Entrance into the cell: Absence or presence of cell wall• For many bacteriophages only the genome and perhaps one or

two proteins penetrate into the cytoplasm itself.• For animal viruses, the entire virion or at least the nucleocapsid

enters the cytoplasm by endocytosis and then must be uncoated.

Site for replication: Cellular compartmentation• No compartmentation in prokaryotes• Compartmentation in eukaryotes (DNA replication and

transcription occur in the nucleus, whereas translation occurs in the cytoplasm)

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mRNA synthesis and protein translation• Polycistronic for bacteria• Monocistronic for eukaryotes

9.11.1 Differences between prokaryotes and eukaryotes that affect virus multiplication

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Uptake of an enveloped virion by an animal cell

9.11.2 Classification of animal viruses

Parvovirus细小病毒 papovavirus乳关多瘤空泡病毒 adenovirus腺病毒 iridovirus虹彩病毒 hepadnavirus嗜肝DNA病毒 poxvirus痘病毒 herpesvirus疱疹病毒

Fig9.23

Picornavirus小核糖核酸病毒 reovirus呼吸道肠道病毒 togavirus外衣病毒 rhabdovirus棒状病毒 orthomyxovirus正粘病毒 bunyavirus布尼亚病毒 coronavirus冠状病毒arenavirus沙粒病毒 retrovirus逆转录病毒 paramyxovirus副粘病毒

The taxonomy of DNA animal viruses

The taxonomy of RNA animal viruses

9.11.3 Consequences of Virus Infection in Animal Cells 病毒感染

动物细胞后的可能后果

宿存感染

潜伏感染

裂解感染

转化为肿瘤细胞

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9.12 Retrovirus 反转录病毒

Figure 9-25

9.12.1 retrovirus structure There are typically seven internal proteins:Four structural proteins

Three enzymatic proteins

Reverse transcriptase

DNA endonuclease (integrase)

Protease

The virion also contains specific cellular tRNAmolecule as primer

Genome: Two identical plus ss RNA5’ capped and 3’ polyadenylatedCapable of acting as mRNA but not used as such Fig 9.25

9.12.2 Genetic map of two typical retroviruses genome

Fig 9.25 Each end of the genomic RNA contains direct repeats (R).

All retroviruses contain the following regions and in the same order: gag, encoding internal structural proteins; pol, encoding reverse transcriptase and integrase; and env, encoding envelope proteins.

src-cancer formation gene

9.12.3 Replication process of a retrovirus 反转录病毒的复制过程

1. Entrance into the cell

2. Virion uncoated3. Reverse

transcription 4. Integration of the

DNA copy into the host genome

5. Transcription of viral DNA into mRNA and viral RNA

6. Encapsidation7. Budding

LTR: long terminal repeats

1. Entrance into the cell

2. Virion uncoated3. Reverse

transcription 4. Integration of the

DNA copy into the host genome

5. Transcription of viral DNA into mRNA and viral RNA

6. Encapsidation7. Budding

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9.12.4 Reverse transcription逆转录

tRNA primer got from previous host cell • Reverse transcrptase is a DNA polymerase and must

have a primer.• The primer for retrovirus reverse transcription is a

specific cellular tRNA. The tRNA used as primer is brought into the viron from the previous host cell.

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V. SUB-VIRAL PARTICLES 亚病毒粒子9.13 Viroids and Prions 类病毒与普列昂

Viroids are small, circular, single-stranded RNA molecules.类病毒是一类小分子的环状RNA分子

• Size: 246 to 399 nucleotides. • Considerable degree of sequence homology (may have

common evolutionary roots)具有高度的同源性（可能有

相同的进化起源）

• Extracellular form: naked RNA, no protein capsid. The RNA contains no protein-encoding genes.胞外形式：裸露的

RNA，无蛋白衣壳，RNA中也无编码蛋白质的基因

Fig 9.27 Structure of viroids. Single-stranded circular RNA can form a seemingly double-stranded structure by intrastrand base-pairing.

Viroid enters the plant through a wound. It is replicated in the host cell nucleus by one of the plant RNA polymerases.

Viroid-infected plants can be symptomless or develop symptoms that range from mild to lethal, depending on the viroid.

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Prions 普列昂

Extracellular form: entirely protein, does not contain any nucleic acid.胞外形式：蛋白质，无核酸

Infectious: cause animals diseases• bovine spongiform encepha’lopathy (mad cow desease)牛海

绵状脑病(疯牛病)• Human Kuru• Human Cretzfeldt-Jakob Disease (CJD)

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Mechanism of Prions

Neuronal cells produce normal prion protein (PrPc)in cell. Abnormally foldedprion protein (PrPsc) can catalyze refolding of PrPc toPrPsc. PrPsc is protease resistant, insoluble, and forms aggregates in neural cells. This eventually leads to destruction of neural tissues and neurological symptoms.

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