Lecture 9-3 Essentials of Virology

Transcription

1 Virus: Growth, quantification, replication and diversity Lecture 9-3 Essentials of Virology CHAPTER 9 in BROCK BIOLOGY OF MICROORGANISMS School of Life Science and Biotechnology, Shanghai Jiao Tong University

2 9.11 Overview of Animal Viruses p.250 section 9.12

3 Shanghai Jiao Tong University 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)

4 Shanghai Jiao Tong University Differences between prokaryotes and eukaryotes that affect virus multiplication mrna synthesis and protein translation Polycistronic for bacteria Monocistronic for eukaryotes

5 Shanghai Jiao Tong University Uptake of an enveloped virion by an animal cell

6 Classification of animal viruses Fig9.23 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

7 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

8 The taxonomy of DNA animal viruses

9 The taxonomy of RNA animal viruses

10 Consequences of Virus Infection in Animal Cells 病毒感染动物细胞后的可能后果 转化为肿瘤细胞 裂解感染 宿存感染 潜伏感染

11 Shanghai Jiao Tong University 9.12 Retrovirus 反转录病毒 Figure 9-25

12 retrovirus structure There are typically seven internal proteins: Genome: Two identical plus ss RNA 5 capped and 3 polyadenylated Four structural proteins Three enzymatic proteins Reverse transcriptase DNA endonuclease (integrase) Protease The virion also contains specific cellular trna molecule as primer Capable of acting as mrna but not used as such Fig 9.25

13 Genetic map of two typical retroviruses genome src-cancer formation gene 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.

14 Replication process of a retrovirus 反转录病毒的复制过程 1. Entrance into the cell 2. Virion uncoated 3. Reverse transcription 4. Integration of the DNA copy into the host genome 5. Transcription of viral DNA into mrna and viral RNA 6. Encapsidation 7. Budding LTR: long terminal repeats

15 1. Entrance into the cell 2. Virion uncoated 3. Reverse transcription 4. Integration of the DNA copy into the host genome 5. Transcription of viral DNA into mrna and viral RNA 6. Encapsidation 7. Budding

16 Shanghai Jiao Tong University 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.

17 Shanghai Jiao Tong University 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

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

19 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.

20 Shanghai Jiao Tong University 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)

21 Shanghai Jiao Tong University Mechanism of Prions Neuronal cells produce normal prion protein (PrP c ) in cell. Abnormally folded prion protein (PrP sc ) can catalyze refolding of PrP c to PrP sc.prp sc is protease resistant, insoluble, and forms aggregates in neural cells. This eventually leads to destruction of neural tissues and neurological symptoms.

22 Shanghai Jiao Tong University