unit 6 – organismal biology part 1: bacteria and viruses
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Unit 6 – Organismal Biology Part 1: Bacteria and Viruses. Are these viruses alive?. A “borrowed” life. Cannot reproduce Cannot carry out metabolic activity outside of a host Exist as “entities” between life-forms and chemical. Virus Structure. - PowerPoint PPT PresentationTRANSCRIPT
Unit 6 – Organismal BiologyPart 1: Bacteria and Viruses
Are these viruses alive?
A “borrowed” life
• Cannot reproduce
• Cannot carry out metabolic activity outside of a host
• Exist as “entities” between life-forms and chemical.
Virus Structure
• Nucleic acid arranged as single linear or circular molecules.– Double-stranded DNA– Single-stranded NA– Double-stranded RNA– Single-stranded RNA
Virus Structure
• Capsid – protein coat that covers the viral genome.– Varies in shape – Built from capsomere protein subunits
Virus Structure
• Envelope– Accessory structure (not found in all)– Membrane w/proteins that surrounds envelop– Derived from host cell
Virus Reproduction
• Limited by the host range– Prokaryotic cells
(bacteria)– Eukaryotic cells
(plants, animals)
• Lock-and-key recognition mechanism (specificity)
General Features
• Virus binds to host cell and viral genome is inserted– Mechanism varies:• Inject DNA • Endocytosis (taken in)• Fusion of viral envelop with host membrane
General Features
• Once genome is inside, viral proteins take over control
• Host provides raw materials and energy to make more viruses
• New viruses exit the cell, damaging or killing it
• This all varies…based on which type of host the virus infect!
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3
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Reproductive Cycles of Bacteriophages
• Phages infect only bacteria
• Two alternative mechanisms:– Lytic Cycle Ends in host death– Lysogenic Cycle Replication
without host death
Lytic CycleIf phage only reproduces this way, it is considered virulent phages. 1
4 3
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Lysogenic Cycle Phages that use both lytic and lysogenic are considered temperate phages.
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53
2
4
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Classes of Animal VirusesDouble-stranded DNA Envelope? Examples/disease
Papovavirus
Herpesvirus
Poxvirus
No
Yes
Yes
HPV (human papillomavirus)
Herpes, shingles, chickenpox
Smallpox, cowpox
Classes of Animal VirusesSingle-stranded DNA Envelope? Examples/disease
Parvovirus No B19 virus
Classes of Animal VirusesDouble-stranded RNA Envelope? Examples/disease
Reovirus No Rotavirus (diarrhea; infants)
Classes of Animal VirusesSingle-stranded RNA Envelope? Examples/diseasePicornavirus
Coronavirus
Flavivirus
No
Yes
Yes
Rhinovirus (common cold); poliovirus; hepatitis A
SARS (Sever Acute Respiratory Syndrome
Yellow fever; West Nile; hepatitis C
Classes of Animal VirusesSingle-stranded RNA – Template for mRNA
Envelope? Examples/disease
Filovirus
Orthomyxovirus
Rhabdovirus
Yes
Yes
Yes
Ebola
Influenza
Rabies
Classes of Animal VirusesSingle-stranded RNA –Template for DNA (*backwards)
Envelope? Examples/disease
Retrovirus Yes HIV (human immunodeficiency virus), AIDS
Retroviruses
• Highly complex reproductive cycle
• Have an enzyme (reverse transcriptase) transcribes RNA template into DNA (opposite direction!)
• HIV causes AIDS (acquired immunodeficiency syndrome)
Viral Disease in Animals
• Some cause host to produce toxins
• Some have toxic molecular components (envelop proteins)
• Difficult to treat once infection occurs– Minimal success with antiviral drugs
Vaccines
• Tool for preventing infection– Harmless variant or derivative of a pathogen– Stimulates immune system response
• Main types– Killed Previously virulent micro-organisms– Attenuated Live micro-orgs w/virus that has
been cultivated to disable virulent properties
Emerging Viruses
• Appear suddenly, new to medical science– Examples: HIV (1980’s); Ebola
• Contributing factors:1. Mutation of existing viruses2. Spread from small, isolated population
(globalization, travel, technology)3. Spread of existing animal viruses to humans
Example: Spanish Flu pandemic (birds humans)
Viroids and Prions
• Simple infectious agents
• Viroids Circular RNA molecules that infect plants– Abnormal growth patterns
• Prions Infection proteins that infect animals– Degenerative brain diseases (scrapie in sheep, mad
cow, Creutzfeld-Jakob in humans)– Transmitted in food
Viroids and Prions
• Prions Infection proteins that infect animals– Degenerative brain diseases • Scrapie (sheep)• Mad cow• Creutzfeld-Jakob (humans)• Kuru (humans)
– Transmitted in food• Example: Beef to human; cannibalisms (New Guinea)