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Ch 13 - Viruses Stephanie Lanoue Learning Objectives:
Differentiate a virus from a bacterium. Describe the chemical and physical structure of both an enveloped and a nonenveloped virus.
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BRAINSTORMING (3-5 minute activity)
Team up with someone near you. Have a piece of paper handy. How many diseases can you think of that are specifically caused by a virus? List them now. Be prepared to share. NOTE: You may use google quickly to double-check your ideas
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Viruses and Human Health
Worldwide Colds Hepatitis Chickenpox Influenza Herpes Warts Ebola Flu (of different varieties) Regional Yellow fever AIDS*****
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What is a Virus exactly? A virus is a small _________ agent that replicates only inside the living cells of other organisms Obligatory intracellular parasites Require __________ host cells to multiply Contain _____ or RNA Contain a protein coat No ribosomes No ATP-generating mechanism
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CLASS DISCUSSION QUESTION Think-Pair-Share (Team up)
How is a virus different from a bacteria? Use your google technology now to look it up! Try to formulate the answer in your own words.
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Figure 13.1 Virus sizes. 800 × 10 nm Bacteriophage M13 970 nm
Bacteriophages f2, MS2 24 nm Ebola virus Poliovirus 30 nm Rhinovirus 30 nm Adenovirus 90 nm 300 nm Chlamydia bacterium elementary body Rabies virus 170 × 70 nm E. coli bacterium 3000 × 1000 nm Prion 200 × 20 nm Human red blood cell 10,000 nm in diameter Bacteriophage T4 225 nm Tobacco mosaic virus 250 × 18 nm Plasma membrane of red blood cell 10 nm thick Viroid 300 × 10 nm Vaccinia virus 300 × 200 × 100 nm
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Viral Structure Virion—complete, ____ developed viral particle
Nucleic acid—DNA or RNA can be single- or double-stranded; linear or circular Capsid—_______ coat made of capsomeres (subunits) Envelope—lipid, _______, and carbohydrate coating on some viruses Spikes—projections from outer surface
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Nucleic acid Capsomere Capsid
Figure Morphology of a nonenveloped polyhedral virus. Nucleic acid Capsomere Capsid
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Nucleic acid Capsomere Envelope Spikes
Figure Morphology of an enveloped helical virus. Nucleic acid Capsomere Envelope Spikes
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Quick Review Question – can you answer this?
What is a capsid? And can you answer this? What is an envelope?
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How Do We Classify Viruses?
Capsid structure and shape Helical viruses—hollow, cylindrical capsid Polyhedral viruses—many-sided Enveloped viruses Complex viruses—complicated structures Type of genetic material ______ Size of the capsid Presence or ________ of an envelope Type of host it infects Animal Plant Target cell Immune cell (HIV) Endothelial cells in blood vessels (Ebola) Type of disease it produces
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Viruses classification (cont’d)
Capsid structure Nucleic acid Capsomere Capsid
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Figure 13.5 Morphology of complex viruses.
65 nm Capsid (head) DNA Sheath Tail fiber Pin Baseplate A T-even bacteriophage Orthopoxvirus
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Viral Multiplication Learning Objectives 3) Describe the lytic cycle of T-even bacteriophages. 4) Describe the lysogenic cycle of bacteriophage lambda.
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Viral Multiplication For a virus to multiply:
It must ______ a host cell It must take over the host's metabolic machinery One-step virus growth curve
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Multiplication of Bacteriophages
Look up on google: What is a phage? Lytic cycle Phage causes lysis and _______ of the host cell Lysogenic cycle Phage DNA is incorporated in the host DNA Phage conversion
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T-Even Bacteriophages: The Lytic Cycle
Attachment: phage attaches by the tail fibers to the _____ cell Penetration: phage lysozyme opens the _____ wall; tail sheath contracts to force the tail core and DNA into the cell Biosynthesis: production of phage _____ and proteins Maturation: assembly of phage particles Release: phage lysozyme breaks the cell wall
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Figure 13.11 The lytic cycle of a T-even bacteriophage.
Bacterial cell wall Bacterial chromosome Capsid DNA Capsid (head) Sheath Attachment: Phage attaches to host cell. Tail fiber Tail Baseplate Pin Cell wall Plasma membrane Penetration: Phage penetrates host cell and injects its DNA. Sheath contracted Biosynthesis: Phage DNA directs synthesis of viral components by the host cell. Tail core Tail DNA Maturation: Viral components are assembled into virions. Capsid Release: Host cell lyses, and new virions are released. Tail fibers
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Bacteriophage Lambda (λ): The Lysogenic Cycle
Lysogeny: phage remains _______ Phage DNA incorporates into _____ cell DNA Inserted phage DNA is known as a prophage When the host cell replicates its chromosome, it also replicates prophage DNA Results in phage conversion—the host cell exhibits new properties
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Figure 13.12 The lysogenic cycle of bacteriophage λ in E. coli.
Phage attaches to host cell and injects DNA. Occasionally, the prophage may excise from the bacterial chromosome by another recombination event, initiating a lytic cycle. Phage DNA (double-stranded) Bacterial chromosome Many cell divisions Lytic cycle Lysogenic cycle Cell lyses, releasing phage virions. Phage DNA circularizes and enters lytic cycle or lysogenic cycle. Lysogenic bacterium reproduces normally. Prophage OR New phage DNA and proteins are synthesized and assembled into virions. Phage DNA integrates within the bacterial chromosome by recombination, becoming a prophage.
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Table 13.3 Bacteriophage and Animal Viral Multiplication Compared
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Reflection – can you answer this?
How does the Lytic cycle differ from the Lysogenic cycle? Instructions: Take 3-4 minutes to review the previous 6 slides covering this topic. Take a moment to craft an answer. Write your response now.
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Viruses and Cancer Learning Objectives 5) Define oncogene cell and give an example.
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Viruses and Cancer Oncogenic viruses become integrated into the ______ cell's DNA and _______ tumors Mechanism is similar to lysogeny in bacteria Ex. Human papillomaviruses (HPV –wart viruses) cause different types of cancers. Cervical cancer, anal cancer A vaccine against HPV for 11 to 12 years girls and boys is recommended
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Plant Viruses, Viroids, and Prions
Learning Objectives 6) Discuss how a protein can be infectious. 7) Differentiate virus, viroid, and perion. 8) Describe plant virus.
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Plant Viruses Plant viruses: enter through _________ or via ________ and transmitted through pollen and seed Plant cells are generally protected from disease by an impermeable cell wall Ex. Tomatoes, potatoes, Tobacco rattle virus (TRV) Tobacco Mosaic Virus (TMV)
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Viroids and Prions Noncellular infection agents Viroids: Prions:
_____ pieces of naked RNA, very small Cause potato spindle tuber disease Prions: ________ infectious proteins. Inherited and transmissible by _______, transplant, and surgical instruments
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Prions and Animals Bovine Spongiform Encephalopathy (BSE)
Mad ____ disease Contaminated _____ Europe when disease can travel to human by infected beef
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Prions and Humans Creutzfeldt-Jakob _________ nervous system
Gradual degeneration __________
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Antiviral agents Difficult to find effective ____________
Because of their _________ Antibiotics don’t affect of viruses (why?) Antiviral drugs _________ viruses replication by targeting the function of host cells Ex. HAV drug, interrupts HIV genetic information incorporate into host cell DNA Double-stranded RNA activated caspase oligomer (DRACO) Viruses destroy themselves Vaccine Stimulate immunity Limited
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Antiviral agents _________ with the phases of viral multiplication.
May ________ a binding site. May disrupt an enzyme or ___________. May interfere with the synthesis of viral parts like DNA, RNA, or protein synthesis.
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