Ch 19- Bacteria and Viruses
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• Prokaryote- unicellular organisms that lacks a nucleus
• How do the two groups of prokayotes differ?
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Make up of cell walls
Archaebacteria lack peptidoglycan, have different membrane lipids
DNA sequence is more like eukaryotes than eubacteria
Thought to be ancestors of eukaryotes
Eubacteria live almost everywhere and archaebacteria live in extremely harsh
environments
• What factors are used to identify prokaryotes?
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Shape
Chemical nature of their cell walls
Movement
How they obtain energy
Identifying Prokaryotes
• Shapes
– Bacilli are rod shaped
– Cocci are spherical shaped
– Spirilla are spiral and corkscrew shaped
• Cell walls- gram staining to tell apart
– Gram positive- thick peptidoglycan walls, appear
violet
– Gram negative- thinner walls, appear pink or light red
• Movement- some move and some don’t
– Flagella- whiplike structures used for movement
Metabolic Diversity
• Heterotrophs- consume organic molecules
made by other organisms
– Chemoheterotrophs- take in organic molecules
– Photoheterotrophs- photosynthetic and take in
organic compounds for carbon source
• Autotrophs- produce own food
– Photoautotrophs
– Chemoautotrophs- do not require light, use
energy from chemical reactions
Growth and Reproduction
• Binary fission- form of asexual reproduction
where cell doubles in size, replicates DNA and
divides in half, produces two identical daughter
cells
• Conjugation- the exchanging of genetic
information between bacteria
• Endospore- forms when growth conditions
become unfavorable
– Bacterium produces thick internal wall, encloses DNA,
remains dormant for months or years
Importance of Bacteria
• What is the importance of bacteria?
– Vital to maintaining living world
– Producers and decomposers
• Decomposers recycle nutrients
• Nitrogen fixation- converting nitrogen gas into form
plants can use
• Used in foods and beverages
• E. coli break down food in intestines
• Bacteria in extreme environments- rich source of heat
stable enzymes
– Medicine, food production, industrial chemistry
Sec 2- Viruses
• What is a virus?
– Composed of core of DNA or RNA surrounded by
protein coat
– Reproduce only by infecting living cells
– Enter living cells, use infected cell to produce more
viruses
– Vary greatly in size and structure
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Capsid- virus’s protein coat
Most are highly specific to cells they infect
Bacteriophages- viruses that infect bacteria
Viral Infection
• Lytic infection- virus enters a cell, makes copies of
itself, and causes the cell to burst
– Injects host cell with viral DNA, mRNA is made by the host
cell from viral DNA into viral particles
• Lysogenic infection- virus integrates its DNA into the
DNA of the host cell
– Viral genetic information replicates along with host cell’s
DNA
– Does not lyse the host cell right away
– Prophage- viral DNA that is embedded in the host’s DNA
– May stay for many generations
Retroviruses
• Viruses that contain RNA as their genetic
information
• Produce a DNA copy of their RNA, inserted
into DNA of host cell
• May remain dormant for lengths of time,
directing production of new viruses-cause
death of new cell
• Responsible for some types of cancer
• Acquired immune deficiency syndrome (AIDS)
Are viruses alive?
• Reproduction
– Only within host cell
• Regulate gene expression
• Genetic code
– DNA or RNA
• Evolve
• Do not………
– Grow or develop
– Obtain and use energy
– Respond to environment
• Viruses are completely dependent upon living things
Sec 3- Diseases Caused by Bacteria and
Viruses
• Pathogens- disease-causing agents
• How do bacteria cause disease?
– Damage the cells and tissues of infected organism directly by
breaking down the cells for food
– Release toxins or poisons that travel throughout the body
interfering with the normal activity of the host
• Mycobacterium tuberculosis- causes tuberculosis, destroys
lung tissue
• Streptococcus- causes strep throat, releases toxins in
bloodstream and can cause scarlet fever
• Corynebacterium diphtheriae- causes diphtheria, releases
toxins into bloodstream that destroy tissue, can lead to
trouble breathing, heart failure
How to prevent disease?
• Vaccine- preparation of weakened or killed
pathogens
– Prompts body to produce immunity to disease
– Immunity- body’s ability to destroy new
pathogens
• Antibiotics- compounds that block the growth
and reproduction of bacteria
– Penicillin
• How can bacterial growth be controlled?
– Sterilization, disinfectants, and food processing
• How do viruses cause disease?
– Produce disease by disrupting the body’s normal
equilibrium
• Many attack and destroy certain cells in body
– Cause symptoms of disease
– Poliovirus
• Other cause cells to change patterns of growth
and development
• Cannot be treated with antibiotics
• Viruses in animals
– Foot-and-mouth disease infected cattle, sheep, and
pigs in Europe in late 90’s
• Viruses in plants
– Tobacco mosaic virus
– Difficult with cell walls
• Viroids- single stranded RNA molecules that have
no surrounding capsids
• Prions- protein infectious particles, contain no
DNA or RNA
– May be cause of mad cow disease