Bio Ch 19

• •Viral genetic material is variable
• –Double-stranded DNA (dsDNA)
• –Single-stranded DNA (ssDNA)
• –Double-stranded RNA (dsRNA)
• –Single-stranded RNA (ssRNA)
• •Either DNA or RNA virus respectively
• From 4 genes to several hundred genes

• •Capsid is the protein shell
• –Shape is variable (rod, polyhedral, etc.)

• •Viral envelope may surround capsid
• –Derived mostly from membrane of host cell
• •Lipid bilayer (host) with proteins (virus/host)
• –Envelope may help cloak virus in host system
• –Allows virus to enter host cell more easily
• •Envelope fuses w/ host plasma membrane
• –New viruses emerge in new envelopes

• •Can only reproduce within certain host
• •Each virus has limited host rang
• –Can only infect certain host cells
• •Viruses recognize receptors on host cells
• •Host range can be single or many species
• –Ex. Swine flu (pigs & humans), rabies (mammals)
• •Viruses can be tissue specific
• Ex. Cold virus affects upper respirators

• Entry and uncoating
• –Viral genome inserted into host cell
• –Viral genome alters host cell activity
• 2. Replication of viral genome
• –Viral hereditary material copied
• –Using host nucleotides, enzymes etc.
• 3.Replication of viral proteins (capsid)
• w/ host enzymes, ribosomes, amino acids etc.
• 4.Assembly & release of new viruses
• –100s-1000s of viruses produced by host
• –Results in cell damage and/or death
• •Host cell often destroyed
• •Contributes to virus symptoms

• –Use reverse transcriptase enzyme
• –Transcribes DNA from RNA template
• –New DNA (viral) then integrates into nucleus
• –ex. HIV targets certain lymphocytes à AIDS

•Severity depends on target tissue–Ex. cold virus affects respiratory epitheliu•Cells can divide and/or repair themselves–Ex. polio virus attacks nerves•Nerve cells do not divide, permanently damaged•Vaccines–Harmless varieties or portions of microbe•ex. Cowpox used to vaccinate against smallpox–Creates immunological memory