Microbiology Module 11.2

• All infective non-cellular agents
• Viruses abundant (over 1 million/milliter)
• -Contain Nucleic Acid and capsid (protective cover)
• -Some viruses have enveloppes derived from CM of -host cell
• -Classified into groups into groups and families based on component differences
• Viroids only infect RNA and infect plant cells
• Virusoids contain RNA and infect animal cells (require helper virus)
• Prions only contain AA and infect animals (infective proteins)

• All require Electron microscope to be seen
• Bacteriophage are viruses that infect prokaryotic cells
• Many phage are larger and more complex than viruses
• Capsids enclose genome and made up of protomers (self assembling subunits)
• Nucleocapsid: Capsid plus genomic material

• Classifies viruses based on type of NA used for genome
• (+)RNA viruses: Have ssRNA that serves as an mRNA
• (-)RNA viruses: Have ssRNA that is compliment of mRNA. Must be replicated before it can be translated
• Retroviruses: ssRNA converted to dsDNA that is inserted into host chromosome

• Are as large as the NA
• NA made and then protomers bind to NA
• Examples: TMV, Influenza

• Contain self assembling capsids. (60-1500 capsomers)
• Protomer: Basic building block
• Capsomer: Made up of 3-5 capsomers
• **Dont worry about numbers

• 1. Attachment (adsorption) to host cell
• 2. Entry into cell
• 3. Viral-directed synthesis of viral components
• 4. Viral assembly (or insertion into host genome)
• 5. Release of fully assembled virions (viral particles)

Attachment events determine host specificitiesMany genes/proteins involved in production of tails

• 1.Tail fibers attach to the OM protein
• 2.Tail structure contracts
• 3.Base plate (lysozyme coated) pushes thru cell wall
• 4.DNA injected into cell

• 1. Fusion: virus bind to particular receptors, triggering a fusion of envelope w/cytoplasm of cell
• 2. Endocytosis: Receptor bound virus w/envelope results in nucleocapsid surrounded by 2 lipid layers
• 3. Endocytosis: Virus w/no envelopes. Same as above
• All require uncoating of virus (can be therapeutic)
• Amantadine prevents uncoating of Influenza A

• DNA Viruses: Make way to nucleus and replicated by host cell DNA polymerases
• RNA Viruses: Translated and must carry gene to make +RNA NAs from either -RNA or DS-DA template
• -RNA viruses must bring replicase enzymes to create +mRNA
• Retroviruses: +RNA viruses. Make & package reverse transcriptase to convert RNA genome into DS-DNA prior to integration into host chromosome

• Lysing: non-enveloped viruses. Lead to short and acute infection
• Budding: Enveloped viruses. Short and chronic infections
• Some dont replicate and leave cell at all, they cause cancer. Cause host cell to de-differentiate causing host cell to replicate uncontrollably

• Flu Caused by 2 species of orthomxoviruses (Type A&B). Type A responsible for most pandemics
• Genome: 8 (-)ssRNAS (11packaged)
• Hosts: Chickens, humans, pigs, horses, birds, sea mammals
• Virions contain hemagglutinin which allows it to attach to respiratory cells
• Neuraminadase break down mucus
• Type B only infect humans and does not have antigenic shifts

• PB1 enzyme is error-prone RNA dependent RNA transcriptase (1 mistake/genome). Responsible for antigenic drift (over flu season, influenza virus mutates w/in a single patient)
• Therapeutic agents: Target neuraminadase, uncoating process.
• Symptoms: Fever, cough, body aches

• Major change in antigenic character of influenza when common host is co-infected w/different new strains
• Shifts are responsible for pandemics such as H1N1

• Used to treat viral infections in Russia. Issue is specificity (only specific to small group of bacteria)
• Used to inhibit bacterial growth in foods. Inhibit lysteria (Deli Meat)
• Used as vectors in biotechnology. AAvs used as vectors in gene therapy
• Lysogenic pathogens harbor prophage that express virulence factors (useful to a bacteria)

• Corynebacterium diphtheriae: Harbors B phage
• Vibrio Cholera: Harbors CTX phage.
• E.Coli: Harbors phage encoding shiga-like toxins
• S. Pyogenes:Causes scarlet fever and necrotizing fascitis
• --All pathogens above only cause disease when harboring the prophage

• Viroid infections caused by small naked RNAs that forms double stranded regions
• Plant pathogens include: Coconut cadang cadand and Chrysanthemum stunt viroid
• Get into cell by wounding. RNA copied by plant RNAp and transcribe viroid RNA
• Virusoids: Only infect animal cells and contain no capsids and encode some proteins. Require helper virus. Example: Hepatitis D

• Infectious Prion: Enriched in Beta-Pleated sheet (43%)
• Noninfectious Prion: 43% Alpha Helix
• Prion proteins go into spinal cord and brain and convert normal prions to infectious forms
• Prion proteins resistant to proteases and disinfectants
• Cause holes in brains and severe immune response
• Scrapie in sheep, CJD in humans, BSE in cows.