Transcript Viruses and Bacteria

Viruses and Bacteria
Not So Harmless
In 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
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Rapid onset
Run a course
Subside
Examples
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Common cold
Influenza
Measles
Mumps
• Latent Infection
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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
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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
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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
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Most prevalent STI
Can lead to sterility
Grow only within other cells
Bacteria is “energy parasite”