viruses and bacteria. not so harmless in the news
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Viruses and Bacteria
Not So HarmlessIn The News
Viruses• Infectious agents
• No cell structure
• Contain DNA or RNA
• Non-living
• Obligate parasites
Properties of Viruses• Can infect all forms of life
• Many infect only one species
Virus Size• Extremely small
• Comparison– Human red blood cell = 10,000 nm– Plasma membrane width 30 nm
Virus Structure• Nucleic acid core
– DNA (double or single stranded)– RNA
Virus Structure• Capsid = protein covering
• Some have envelope over capsid
Tobacco Mosaic Virus
Herpes Virus
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
Ways Viruses Cause Disease• Can initiate cancer
• Can take over cell function
Cancer & Viruses• Some viruses initiate cancer
• Virus causes cell changes
• Virus does not “carry” cancer
Viruses as Pathogens
• Disrupt cell functions
• Use cells to make more virus
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
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
Prions & Viroids• Infectious agents
• Simpler than viruses
Prions
• Proteins that cause disease
• Only infectious agent with no nucleic acid
• Examples: – Bovine spongiform encephalopathy
• mad cow disease
– Creutzfeldt-Jacob disease
Healthy Brain Tissue Prion-infected Brain Tissue
Viroids• Small strands of RNA
• No protein coats
• Replicated in host cells
• Known to cause plant diseases
Bacteria• Prokaryotic cells
• Some harmful, some helpful
• Present virtually everywhere
Characters of Bacteria• No membrane-bound nucleus
• No membrane-bound organelles
Modes of Nutrition in Bacteria
• Photoautotrophic
• Chemoautotrophic
• Hetrotrophic
Photoautotrophs
• Produce food via photosynthesis
• Green & purple bacteria, cyanobacteria
• Cyanobacteria probably oxygenated Earth’s atmosphere
Chemautotrophs
• Energy from inorganic molecules
• Manufacture growth factors– Carbohydrates – Fats – Proteins – Nucleic acids
• Important in nitrogen cycling
Heterotrophs
• Feed on other organisms
• Play key role in carbon cycling
• Many bacteria are decomposers
• Release CO2 used by photosynthesizers
Archaea
• Prokaryotic cells
• Not bacteria
• None cause disease
• Often in harsh habitats
Reproduction in Bacteria• Asexual binary fission
Bacterial Disease
• Attach to cells
• Cause tissue damage
• Some plant diseases
• Many human diseases
Syphilis
• Caused by spiral bacterium
• Sexually transmitted
• Curable with penicillin
• Can cause death if untreated
Stages of Syphilis
• Primary – Hard chancre sore– Becomes painful
• Secondary – 6 weeks – months– Dispersed thru body– Lesions at other sites
Stages of Syphilis• Latent stage
– No symptoms– May last a lifetime
• Tertiary stage– New lesions – tumor-like– Paralysis and death
Gonorrhea
• Sexually transmitted
• May exhibit few symptoms
• Can cause sterility
Clamydia• Most prevalent STI
• Can lead to sterility
• Grow only within other cells
• Bacteria is “energy parasite”