Viruses and Bacteria. Not So Harmless In The News.
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Transcript of Viruses and Bacteria. Not So Harmless In The News.
![Page 1: Viruses and Bacteria. Not So Harmless In The News.](https://reader035.fdocuments.net/reader035/viewer/2022062802/56649ebc5503460f94bc5ba8/html5/thumbnails/1.jpg)
Viruses and Bacteria
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Not So HarmlessIn The News
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Viruses• Infectious agents
• No cell structure
• Contain DNA or RNA
• Non-living
• Obligate parasites
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Properties of Viruses• Can infect all forms of life
• Many infect only one species
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Virus Size• Extremely small
• Comparison– Human red blood cell = 10,000 nm– Plasma membrane width 30 nm
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Virus Structure• Nucleic acid core
– DNA (double or single stranded)– RNA
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Virus Structure• Capsid = protein covering
• Some have envelope over capsid
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Tobacco Mosaic Virus
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Herpes Virus
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Replication of Viruses• Cannot multiply outside cells
• Uses cell organelles to multiply
• Process is called lytic cycle
• Lysogenic cycle– Long term relationship of cell & virus– Viral nucleic acid replicates as cell multiplies
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Ways Viruses Cause Disease• Can initiate cancer
• Can take over cell function
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Cancer & Viruses• Some viruses initiate cancer
• Virus causes cell changes
• Virus does not “carry” cancer
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Viruses as Pathogens
• Disrupt cell functions
• Use cells to make more virus
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Viral Infections
• Acute infection– Rapid onset– Run a course– Subside– Examples
• Common cold• Influenza• Measles • Mumps
• Latent Infection– Infective agent present– Not manifesting disease– Causes latent infections– Examples
• Herpes • HIV
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Genital Herpes• Common STD
– More than 1 in 5 age 12 & over in U.S.– Caused by herpes simplex virus– Develops a few days after sexual contact– Spreads when virus is active – Lesions develop– Latent infections
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Prions & Viroids• Infectious agents
• Simpler than viruses
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Prions
• Proteins that cause disease
• Only infectious agent with no nucleic acid
• Examples: – Bovine spongiform encephalopathy
• mad cow disease
– Creutzfeldt-Jacob disease
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Healthy Brain Tissue Prion-infected Brain Tissue
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Viroids• Small strands of RNA
• No protein coats
• Replicated in host cells
• Known to cause plant diseases
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Bacteria• Prokaryotic cells
• Some harmful, some helpful
• Present virtually everywhere
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Characters of Bacteria• No membrane-bound nucleus
• No membrane-bound organelles
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Modes of Nutrition in Bacteria
• Photoautotrophic
• Chemoautotrophic
• Hetrotrophic
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Photoautotrophs
• Produce food via photosynthesis
• Green & purple bacteria, cyanobacteria
• Cyanobacteria probably oxygenated Earth’s atmosphere
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Chemautotrophs
• Energy from inorganic molecules
• Manufacture growth factors– Carbohydrates – Fats – Proteins – Nucleic acids
• Important in nitrogen cycling
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Heterotrophs
• Feed on other organisms
• Play key role in carbon cycling
• Many bacteria are decomposers
• Release CO2 used by photosynthesizers
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Archaea
• Prokaryotic cells
• Not bacteria
• None cause disease
• Often in harsh habitats
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Reproduction in Bacteria• Asexual binary fission
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Bacterial Disease
• Attach to cells
• Cause tissue damage
• Some plant diseases
• Many human diseases
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Syphilis
• Caused by spiral bacterium
• Sexually transmitted
• Curable with penicillin
• Can cause death if untreated
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Stages of Syphilis
• Primary – Hard chancre sore– Becomes painful
• Secondary – 6 weeks – months– Dispersed thru body– Lesions at other sites
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Stages of Syphilis• Latent stage
– No symptoms– May last a lifetime
• Tertiary stage– New lesions – tumor-like– Paralysis and death
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Gonorrhea
• Sexually transmitted
• May exhibit few symptoms
• Can cause sterility
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Clamydia• Most prevalent STI
• Can lead to sterility
• Grow only within other cells
• Bacteria is “energy parasite”
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