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What is viral genetics?
viruses and viroids are nonliving particles with nucleic acid genomes that require the assistance of living cells to reproduce
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What is viruses?
- A) small infectious particle that consists of nucleic acid enclosed in a protein coat
- B) over 4000 different types
- C) vary greatly in their characteristics, host range, structure and genome composition
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What is the difference about their structural?
- All have a capsid (protein coat) but it varies in shape and complexity
- Some have viral envelope derived from host cell plasma membrane
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What kind of Genome of Viruses have?
- DNA vs RNA
- Single stranded vs Double stranded
- Linear vs Circular
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What about their reproduction?
Viruses are not alive therefore they are not cells or composed of cells. They also cannot carry out metabolism on their own.
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The basic steps of viruses are:
- Attachment
- Entry
- Intregration
- Synthesis of viral components
- Viral assembly
- Release
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What is the attachment?
Usually specific for one kind of cell due to binding to specific molecules on cell surface
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What about the entry?
- Bacteriophages or phage to injects only DNA into bacteria
- HIV fuses with host membrane and the entire virus enters
- Some viral genes are expressed
- Virus may integrate into host chromosome
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What about integration?
- It cuts host chromosomal DNA and insert viral genome.
- Phage in bacterial DNA called prophageHIV is an RNA Virus and integrates as a provirus
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What is the synthesis of viral components?
- Host cell enzymes such as DNA polymerase make alot copies of the phage DNA; transcribe the genes within these copies into mRNA.
- DNA provirus is not excised from hose chromosome instead it is transcribed in the nucleus to produce many copies of viral RNA.
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Viral assembly
- Some viruses can self-assemble
- Proteins modify capsid proteins or serve as scaffolding
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Release
- Phages must lyse their host cell to escape.
- Enveloped viruses bud from the host cell.
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What is lysogency?
latency in bacteriophages. When host replicates, also copies prophage.
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What is the lysogenic cycle?
Integration, replication and excision
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What is the lytic cycle?
Synthesis, assembly and release
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Temperate Phages
have a lysogenic cycle.
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Virulent phages
do not have lysogenic cycle.
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Viriods
- Composed solely of single-stranded circular RNA molecules
- Infect plant cells
- Some replicate in host cell nucleus, others in chloroplast
- RNA genome does not code for proteins
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Prions
- Composed entirely of proteins
- Proteinaceous infectious agent
- Dz causing conformation PrPScConverts normal proteins to abnormal conformation
- Several types of neurodegenerative dz of human and livestock such as TSE (transmissible spongiform encephalopathies)
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