Ch18 Genetics Viruses
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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
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
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
What kind of Genome of Viruses have?
- DNA vs RNA
- Single stranded vs Double stranded
- Linear vs Circular
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.
The basic steps of viruses are:
- Synthesis of viral components
- Viral assembly
What is the attachment?
Usually specific for one kind of cell due to binding to specific molecules on cell surface
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
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
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.
- Some viruses can self-assemble
- Proteins modify capsid proteins or serve as scaffolding
- Phages must lyse their host cell to escape.
- Enveloped viruses bud from the host cell.
What is lysogency?
latency in bacteriophages. When host replicates, also copies prophage.
What is the lysogenic cycle?
Integration, replication and excision
What is the lytic cycle?
Synthesis, assembly and release
have a lysogenic cycle.
do not have lysogenic cycle.
- 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
- 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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