Questions and Answers
What is the process by which genetic material is transferred between prokaryotic cells?
Which of the following is an example of horizontal gene transfer?
What is the term for the process by which some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3)?
Which of the following prokaryotes require oxygen for cellular respiration?
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What is the term for the process by which a prokaryotic cell takes up and incorporates foreign DNA from the surrounding environment?
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Which of the following is an example of a nutrient source for heterotrophs?
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What is the term for the exchange of genetic material between bacteria through the agency of viruses?
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Which of the following is a characteristic of obligate anaerobes?
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What is the primary function of chemoheterotrophic prokaryotes in ecosystems?
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What is the term for archaea that thrive in very hot environments?
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Which type of bacteria is known for being the smallest known cells?
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What is the primary difference between methanogens and other archaea?
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What is the term for the process by which prokaryotes increase the availability of nitrogen, phosphorus, and potassium for plant growth?
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Which type of bacteria is known for causing syphilis?
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What is the term for archaea that live in highly saline environments?
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Which type of bacteria is known for being photoautotrophs that generate O2?
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What is the primary function of the peptidoglycan layer in bacterial cell walls?
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What is the main difference between Gram-positive and Gram-negative bacteria?
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What is the primary mechanism of generating genetic diversity in bacteria?
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What is the primary source of energy for most prokaryotes?
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What is the function of a capsule in prokaryotes?
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What is the primary difference between prokaryotic and eukaryotic cell walls?
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What is the purpose of the Gram stain in microbiology?
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What is the primary function of plasmid DNA in prokaryotes?
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What is the main function of fimbriae and pili in bacteria?
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What is the composition of the innermost layer of a bacterium?
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What is the primary difference between gram-positive and gram-negative bacteria?
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What is the function of lipoteichoic acid in gram-positive bacteria?
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What is the purpose of the Gram stain in microbiology?
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What is the function of the cell wall in bacteria?
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What is the composition of the outer cell membrane in gram-negative bacteria?
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What is the function of the capsule in bacteria?
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What is the primary reason why fresh cultures are used in the Gram stain procedure?
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What is the purpose of adding Gram's iodine in the Gram stain procedure?
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What is the role of the thick peptidoglycan layer in Gram positive cells?
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What is the effect of ethanol on the peptidoglycan layer in Gram positive cells?
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What is the purpose of adding safranin in the Gram stain procedure?
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What is the primary difference between Gram positive and Gram negative bacteria in terms of their cell wall structure?
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What is the primary mechanism by which antibiotics kill bacteria?
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What is the consequence of overusing antibiotics in livestock?
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What is the purpose of Alexander Fleming's discovery of penicillin?
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What is the Mega-Plate Experiment designed to study?
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What is a common misuse of antibiotics?
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What can contribute to the development of antibiotic-resistant bacteria?
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What is a characteristic of Alexander Fleming's view of bacteria?
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What is a consequence of the overuse of antibiotics?
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Which of the following processes involves the direct transfer of DNA between bacteria through a mating bridge?
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What is the primary function of the plasmid in bacterial conjugation?
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Which of the following types of phages can give bacteria 'superpowers'?
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What is the primary difference between the bacterial chromosome and the plasmid?
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Which of the following processes is exclusive to Streptococcus pneumoniae, H. influenzae, and Neisseria?
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What is the primary mechanism of DNA transfer in transduction?
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Which of the following is a result of transposition?
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What is the primary function of the bacterial plasmid in genetic transfer?
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What is the characteristic that distinguishes Domain Bacteria from the other two domains of life?
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Which of the following is a characteristic shared by Domain Eukarya and Domain Archaea?
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What is the term for the subdivision of Archaea that includes thermophiles?
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Which of the following is an example of a domain that is found in almost every environment on Earth?
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What is the term for the process by which Domain Eukarya and Domain Archaea share a common ancestor?
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Which of the following is a characteristic unique to Domain Archaea?
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What is the term for the type of RNA polymerase found in Domain Eukarya and Domain Archaea?
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Which of the following is an example of a methanogen?
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Study Notes
Genetic Recombination
- Prokaryotic cells can take up and incorporate foreign DNA from the surrounding environment through transformation
- Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)
- Horizontal gene transfer is the movement of genes among individuals from different species
- Conjugation is the process where genetic material is transferred between prokaryotic cells, requiring a pilus and the F factor for DNA transfer
Metabolism and Nutrition
- Prokaryotes can be categorized by how they obtain energy and carbon:
- Phototrophs obtain energy from light
- Chemotrophs obtain energy from chemicals
- Autotrophs require CO2 as a carbon source
- Heterotrophs require an organic nutrient to make organic compounds
- Energy and carbon sources combine to give four major modes of nutrition
- Nitrogen is essential for the production of amino acids and nucleic acids
- Nitrogen fixation: some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3)
- Cyanobacterium Anabaena has photosynthetic cells and nitrogen-fixing cells called heterocysts that exchange metabolic products
Prokaryotic Diversity
- Domain Archaea:
- Share traits with bacteria and eukaryotes
- Some live in extreme environments (extremophiles)
- Extreme halophiles (Clade Euryarchaeota) live in highly saline environments
- Extreme thermophiles (Clade Crenarchaeota) thrive in very hot environments
- Methanogens (Clade Euryarchaeota) live in swamps and marshes, producing methane as a waste product, and are strict anaerobes poisoned by O2
- Domain Bacteria:
- Proteobacteria: gram-negative, include photoautotrophs, chemoautotrophs, and heterotrophs, some anaerobic and others aerobic
- Chlamydia: parasites that live only within animal cells
- Spirochetes: helical heterotrophs, some parasitic
- Cyanobacteria: photoautotrophs that generate O2
- Gram-positive bacteria: include Actinomycetes, Bacillus anthracis, Clostridium botulinum, Staphylococcus, Streptococcus, and Mycoplasms
Ecological Importance
- Prokaryotes play a major role in chemical recycling, decomposing dead organisms and waste products
- Chemoheterotrophic prokaryotes increase the availability of nitrogen, phosphorus, and potassium for plant growth
- Symbiosis: an ecological relationship between a larger host and smaller symbiont, such as bacteria and Archaea
Bacterial Structure
- Bacteria come in three main shapes: coccus (circular), bacillus (rod-shaped), and spiral.
Flagella and Hair-Like Appendages
- Flagella are thin, rigid filaments that enable bacterial movement by propelling the bacteria forward or moving it around.
- Fimbriae and pili are hair-like appendages used for binding to cell surfaces, contributing to disease causation, and bacterial conjugation.
Layers of a Bacterium
- The capsule is the outermost layer, containing polysaccharides that enable binding to cell surfaces and avoid phagocytosis.
- The plasma membrane is a semi-permeable membrane allowing transportation of substances in and out of the cell, similar in bacteria and humans, consisting of a phospholipid bilayer with proteins.
- The cell wall is a complex, semi-rigid structure that enables classification into gram-positive and gram-negative bacteria.
Cell Wall Composition
- Gram-positive bacteria have a thick peptidoglycan layer above the cell membrane and lipoteichoic acid, which enables binding to cell walls and recognition by macrophages.
- Gram-negative bacteria have a thin peptidoglycan layer, an extra outer cell membrane, and lipid-like structures (lipoproteins and lipid A) that can cause diseases and shock syndromes.
Gram Staining
- Gram staining is used to classify bacteria based on cell wall composition, involving crystal violet, iodine, decolorization with alcohol, and safranin.
- Gram-positive bacteria stain purple, while gram-negative bacteria stain pinkish-red.
Cytoplasm
- Cytoplasm contains water, enzymes, ribosomes, and circular DNA.
- Ribosomes are the site of protein synthesis and are found throughout the cytoplasm.
- Bacterial DNA is circular, unlike the linear DNA found in eukaryotes (except for mitochondrial DNA).
- Plasmids are small, circular genetic materials found in the cytoplasm, which can be incorporated into the main DNA or transferred between bacteria through conjugation.
Gram Stain Procedure
- Fresh cultures are required for Gram staining, as aged cells lose their ability to retain the stain
- Cells are prepared on a slide by drying and fixing with a Bunsen burner flame
- Crystal violet stain is applied for 30-40 seconds, followed by a rinse with water
- Gram's iodine solution combines with crystal violet to form a dye complex
- Decolorization is achieved with ethanol or acetone, which removes the dye complex from Gram negative bacteria
- Decolorization is stopped when the drop coming off the edge of the slide becomes colorless
- A counter stain of safranin is used to stain Gram negative bacteria pink
Mechanism of Gram Stain
- The Gram stain is correlated with bacterial cell wall structure
- Thick peptidoglycan layer in Gram positive cells acts as a permeability barrier, retaining the crystal violet iodine complex
- Ethanol shrinks the thick peptidoglycan layer, allowing it to retain the dye
- Thin peptidoglycan layer in Gram negative cells has large pores, allowing ethanol to extract lipids and increase porosity, removing the crystal violet iodine complex
Antibiotics and Bacteria
- Antibiotics are natural substances produced by microbes to kill other microbes, used for billions of years.
The Discovery of Penicillin
- Alexander Fleming discovered penicillin in 1928 by accident when a mold landed in one of his bacterial cultures.
- He isolated the chemical and called it penicillin, revolutionizing medicine and saving millions of lives from infections.
The Dark Side of Antibiotics
- Most commercial antibiotics destroy not only bad bacteria but also many other microbes living in the gut.
- This leads to the growth of malevolent microbes like Salmonella, Campylobacter, and Clostridium difficile.
The Problem of Antibiotic Misuse
- Antibiotic misuse creates invincible super bugs, bacteria that have evolved to resist antibiotics.
- Overuse of antibiotics drives the evolution of resistant bacteria, making them less effective against infections.
The Mega-Plate Experiment
- Scientists Michael Baym, Tami Lieberman, and Roy Kishony studied antibiotic resistance using a giant petri dish.
- They grew E.coli bacteria on the dish, introducing different concentrations of antibiotics to observe resistance evolution.
- The bacteria evolved super resistance to antibiotics in just 11 days.
Consequences of Antibiotic Overuse
- Antibiotics are often misused to treat viral diseases like colds and flu, which they are ineffective against.
- Overuse of antibiotics leads to the growth of resistant bacteria in livestock, spreading to humans.
- Antibacterial chemicals in soaps, hand gels, and toys contribute to the problem.
Alexander Fleming's Legacy
- Fleming appreciated the beauty of bacteria, creating germ art using microbes as his medium.
- He recognized that bacteria could be helpful and were everywhere.
Bacterial Genetics
- Bacterial DNA is composed of two parts: the larger, complex bacterial chromosome and the smaller bacterial plasmid
- The bacterial chromosome contains most of the bacterial DNA, while the plasmid is a smaller, separate piece of DNA that floats inside the bacteria
Transposition
- Involves the extraction of a small part of the bacterial chromosome to become a plasmid or the reintegration of a plasmid into the bacterial chromosome
- Plasmids play a crucial role in this process due to their small size and accessibility
- Bacteria can only share their plasmid, not their chromosome, with other bacteria
Conjugation
- F+ bacteria have a sex pilus, encoded by their plasmid, which allows them to form a mating bridge with F- bacteria
- F+ bacteria transfer a copied plasmid, encoding for the sex pilus, to F- bacteria
- Both bacteria then have a plasmid encoding for a sex pilus and become F+
- Conjugation allows for the horizontal transfer of genetic material between bacteria
Transformation
- This process, also known as competence, enables bacteria to take up naked DNA or genomes from their environment and utilize it
- Bacteria can acquire antibiotic resistance genes from their environment and become antibiotic resistant
- Only certain species, such as Streptococcus pneumoniae, H.influenza, and Neisseria, are capable of transformation
Transduction
- Occurs when a bacteriophage (bacterial virus) injects its own DNA into the bacterial DNA
- The viral DNA is integrated into the bacterial DNA and begins replicating the virus
- Lytic phages kill the bacteria, while lysogenic phages do not and can confer "superpowers" on the bacteria
- Lysogenic phages can enable bacteria to produce exotoxins
Domain of Life: Phylogenetic Tree
- The phylogenetic tree represents three main domains of life: Eukarya, Archaea, and Bacteria
- Eukarya and Archaea share a common ancestor, forming a sister taxa relationship
- Bacteria is distinct from Eukarya and Archaea
Similarities between Archaea and Eukarya
- Both have RNA polymerase, but with different types
- Both use methionine as the start amino acid during protein synthesis
- Both have histones, proteins that organize DNA
- Both have linear chromosomes with telomeres
Domain Archaea
- Found in extreme environments, such as hot springs, salt lakes, and deep-sea vents
- Includes Halophiles (salt-loving), Thermophiles (heat-loving), and Methanogens (methane-producing)
- Subdivided into Crenarchaeota (thermophiles) and Euryarchaeota (methanogens and halophiles)
Domain Bacteria
- Found in almost every environment on Earth, including soil, water, and human skin
- Includes Proteobacteria, Chlamydia, Spirochetes, Cyanobacteria, and Gram-positive bacteria
- Subdivided into Alpha Proteobacteria, Beta Proteobacteria, Gamma Proteobacteria, Delta Proteobacteria, and Epsilon Proteobacteria
Bacterial Diversity and Ecological Impact
- Play a crucial role in ecosystems, including nitrogen fixation, decomposition, and primary production
- Responsible for diseases, such as tuberculosis, syphilis, and Lyme disease
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Description
This quiz covers various ways genetic material is transferred between prokaryotic cells, including transformation, transduction, and conjugation. It explains the role of bacteriophages and horizontal gene transfer.