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Viruses (2)Biology 11 Mr. McCallum
What do viruses do?
Replicate, replicate, replicate! Harmful as this leads to the death of the host cell
Attachment: Attaching to cell specific « structures » on the cell’s surface via specific « structures » on the virus’ surface
Penetration: Entire virus enters the host cell, OR the genetic material is injected into the cell *ultimate result of viral infection – exposure of the
virus’ genetic material inside the host cell
What do viruses do? (continued)
Transcription and Replication: Virus takes over the machinery of the cell, making nothing but viral parts
Assembly: Viral parts being produced are assembled into complete viruses
Release: Exit cell through « budding » - few viruses at a time leaving the cell , OR through lysis – cellular membrane ruptures, releasing all viral particles at once
Infection
Everything living that we know today is susceptible to viral infection. Plants, animals, bacteria Multi-cellular, single-celled
Specificity Smallpox (humans), influenza (humans and a few
other animals), tobacco mosaic virus (particular plants), lambda bacteriophage (E. coli)
Viral Taxonomy
Variety of shapes, sizes, and organization of basic genetic material
Arrangement and type of genetic material used for sub-classification
ALL: Capable of replicating within a living cell and can produce offspring that are usually identical to the original virus
Mutation
During replication, mutation can occur. Can render virus no longer functional Volume of offspring negates these effects
Mutations can benefit the virus New strains (Influenza virus) Difficult for vaccinations
Protection When viruses infect our cells, our body responds by
creating and secreting inteferons
Inteferons: Proteins that interact with adjacent cells to aid in their resistance to viral infection
If this is not enough, we experience disease
Our immune system targets and kills cells infected by viruses They need a living host to replicate!
Protection (2) Usually, our immune system removes the virus
HIV is an exception – they use immune cells as their living hosts
Agents isolated from natural sources are capable of killing a virus Acyclovir – inhibits Herpesvirus replication AZT and HIV protease inhibitor inhibit HIV replication
Plants have substances that coat leaves and stems, closing off systems – walling off the infection
Bacteria use enzymes within their cells Bacteriophages often suceed at killing bacterial cells in
short time frames
Viral Infection - Lytic
Results in the destruction of the infected cell and its membrane (cell lyses)
Viral DNA exists separately, and is replicated independently from the host cell DNA
Many viruses produced and released into the environment simultaneously
Viral Infection – Lysogenic
Does not lyse the host cell, immediately
Integration of viral DNA into the host genome
Transmitted to daughter cells at each division
Remain “dormant” – host living normally until later event initiates viral release Changes in temperature,
available nutrients, UV raditation, certain chemicals, etc.
Lysogenic and Lytic Cycles