Ch18 Genetics Viruses
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Ch18 Genetics Viruses
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
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
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
HIV is an
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
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
Infect plant cells
Some replicate in host cell nucleus, others in chloroplast
code for proteins
Composed entirely of proteins
Proteinaceous infectious agent
Dz causing conformation PrP
Converts normal proteins to abnormal conformation
Several types of neurodegenerative dz of human and livestock such as TSE (transmissible spongiform encephalopathies)