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Questions and Answers
What is the most diverse group of organisms?
How do all prokaryotic cells reproduce?
What is the primary method of division for prokaryotic cells?
What is the basis for modern prokaryotic classification?
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What is a characteristic of Archaea?
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What type of organisms require extreme conditions of temperature, pH, and/or salinity to survive?
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What is the function of methanogens?
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What is a characteristic of Lactobacillus?
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What is a characteristic of Staphylococcus?
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What type of bacteria lack cell walls?
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Study Notes
Prokaryotes
- Most diverse group of organisms
- Can be found in various habitats, including:
- Antarctic glaciers to thermal hot springs
- Colons of animals to cytoplasm of other prokaryotes
- Distilled water to supersaturated brine
- Disinfectant solutions to basalt rocks
- Only a few capable of colonizing humans and causing disease
Morphology of Prokaryotic Cells
- Various shapes, including:
- Coccus
- Coccobacillus
- Bacillus
- Vibrio
- Spirillium
- Spirochete
- Pleomorphic
Reproduction of Prokaryotic Cells
- All reproduce asexually
- Three methods:
- Binary fission (most common)
- Snapping division
- Budding
Arrangements of Prokaryotic Cells
- Result from two aspects of division during binary fission
- Planes in which cells divide:
- Cocci divide in multiple places, bacilli in only one
- Separation of daughter cells
Modern Prokaryotic Classification
- Based on genetic relatedness of rRNA sequences
- Three domains:
- Archaea
- Bacteria
- Eukarya
Survey of Archaea
- Common features:
- Lack peptidoglycan
- Cell membrane lipids have branched hydrocarbon chains
- Lack tRNA specific for thymine
- AUG codon codes for methionine
- Reproduce by:
- Binary fission
- Budding
- Fragmentation
- Most are:
- Cocci
- Bacilli
- Spiral forms
- Unusual shapes exist
- Not known to cause disease in humans or animals
Extremophiles
- Require extreme conditions of:
- Temperature
- pH
- Salinity
- To survive
- Prominent members:
- Thermophiles
- Halophiles
Thermophiles
- DNA, RNA, cytoplasmic membranes, and proteins do not function properly below 45°C
- Hyperthermophiles require temperatures over 80°C
Halophiles
- Inhabit extremely saline habitats
- Depend on greater than 9% NaCl to maintain integrity of cell walls
- Contain red or orange pigments for protection from:
- Visible light
- UV light
- Most studied: Halobacterium salinarium
Methanogens
- Convert carbon dioxide, hydrogen gas, and organic acids to methane gas
- Largest group of archaea
- Convert organic wastes in:
- Pond sediments
- Lake sediments
- Ocean sediments
- To methane
- Some live in colons of animals, contributing to environmental methane
- Have produced ~10 trillion tons of methane buried in mud on ocean floor
Low G+C Gram-Positive Bacteria
Clostridia
- Rod-shaped, obligate anaerobes
- Important in medicine and industry
- Produce toxins that cause diseases in humans
- Endospores survive harsh conditions
- Related microbes:
- Epulopiscium
- Sulfate-reducing microbes
- Selenomonas
Mycoplasma
- Facultative or obligate anaerobes
- Lack cell walls
- Smallest free-living cells
Bacillus
- Endospore-forming aerobes and facultative anaerobes
- Many common in soil
- Bacillus thuringiensis toxin is used as an insecticide
- Bacillus anthracis causes anthrax
- Other species synthesize antibiotics
Listeria
- Contaminates milk and meat products
- Can reproduce under refrigeration
- Survives inside phagocytic white blood cells
- Rarely causes disease in adults
- Can kill the fetus if crosses the placenta in pregnant women
Lactobacillus
- Grows in the human mouth, stomach, intestinal tract, and vagina
- Rarely causes disease
- Inhibits the growth of pathogens within the body
- Used in the production of various foods
Streptococcus and Enterococcus
- Cause numerous diseases
- Various strains of multi-drug-resistant streptococci
Staphylococcus
- One of the most common inhabitants of humans
- Produces toxins and enzymes that contribute to disease
High G + C Gram-Positive Bacteria
Corynebacterium
- Pleomorphic aerobes and facultative anaerobes
- C.diptheriae causes diptheria
Mycobacterium
- Aerobic rods that sometimes form filaments
- Slow growth, partly due to mycolic acid in cell walls
- Some species are pathogens of animals and humans
Actinomycetes
- Form branching filaments resembling fungi
- Cause disease primarily in immunocompromised patients
- Important genera
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Description
This quiz covers the diversity of prokaryotes, their habitats, and the morphology of prokaryotic cells, including different shapes and forms.
