8. Bacteria & Archaea (V)

Which two domains contain prokaryotes?

Bacteria and Archaea.

Which taxonomic level is the largest and most inclusive grouping in the hierarchical classification system?

Domain.

Which domain is more closely related to the eukaryotes (us and all the other eukaryotes)?

Archaea.

Approximately how old did bacteria and prokaryotes first evolve?

About 3.7 billion years ago.

Do bacteria have a nuclear membrane or membrane-bound organelles?

No; they lack a nuclear membrane and membrane-bound organelles.

Describe the general structure of the bacterial chromosome.

Circular DNA, essentially one large DNA molecule, not like eukaryotic chromosomes.

What are the three main shapes of bacteria and their names?

Rod-shaped (bacillus; bacilli for plural), spherical (coccus/cocci), and spiral-shaped (spirillum; spirula for plural).

What is a bacterial capsule and what does it do?

A sticky outer layer outside the cell wall that helps bacteria stick to surfaces and may provide protection.

What are fimbriae and how do they differ from a pilus?

Fimbriae are short extensions that help with sticking to surfaces; a pilus is a longer appendage used to exchange DNA between bacteria.

Are bacterial flagella homologous to eukaryotic flagella?

No; they are not homologous, though they serve the same function (movement).

Do bacteria have mitochondria or chloroplasts?

No; they lack membrane-bound organelles like mitochondria and chloroplasts. They perform respiration and photosynthesis inside the cell, often via infolded membranes.

What is a biofilm?

A community of bacteria (often multiple species) living together on a surface; examples include dental plaque and biofilms on toothbrushes or lab equipment.

What is a plasmid in bacteria?

A small, circular extra DNA molecule that carries non-essential genes that can help bacteria survive in hostile conditions (e.g., antibiotic resistance).

What is membrane infolding and why is it advantageous for some bacteria?

Portions of the cell membrane fold inward, increasing surface area to support processes like respiration or photosynthesis (e.g., respiratory membranes and thylakoid membranes).

What is taxis, and what are two examples mentioned?

Directed movement toward or away from a stimulus; examples include chemotaxis (toward/away from chemicals) and phototaxis (toward/away from light).

What is the typical size of bacteria?

About one micrometer or smaller.

Why are bacteria described as ubiquitous and in large numbers in the human body?

They are absolutely everywhere; estimates suggest there are ten times more bacterial cells than human cells in and on the body.

What is the main function of the bacterial cell wall?

To protect the cell and prevent bursting from osmotic water uptake; it is rigid and resists turgor pressure.

What molecule makes up the bacterial cell wall in most bacteria?

Peptidoglycan, a sugar polymer with polypeptide crosslinks.

What are the two main categories of bacteria based on cell wall structure?

Gram-positive and gram-negative.

Describe the Gram-positive cell wall structure.

Plasma membrane plus a thick peptidoglycan layer outside; stains purple with Gram stain.

Describe the Gram-negative cell wall structure.

Plasma membrane, a thin peptidoglycan layer, and an outer membrane with carbohydrate-containing components; Gram stain does not stay, appearing pink.

Why are Gram-negative bacteria sometimes more resistant to antibiotics?

Their outer membrane provides extra protection against certain antibiotics.

What is an endospore?

A durable, dormant form that forms inside the bacterial cell to protect DNA under harsh conditions.

How does endospore formation occur?

Under hostile conditions, the cell encases its DNA in a protective coating, the rest of the cell disintegrates, forming an endospore.

Which genus is commonly cited as forming endospores (e.g., Bacillus anthracis)?

Bacillus; Bacillus anthracis is the species associated with anthrax.

What does 'endo' mean in endospore?

Inside; the endospore forms inside the cell.

Where can endospores be found and what risk do they pose?

In soil; they can enter open wounds or be inhaled and cause severe infections, including anthrax.

How long can endospores survive in harsh conditions?

Up to thousands of years.

What causes Gram-positive bacteria to appear purple under Gram staining?

The thick peptidoglycan layer traps the crystal violet stain.

What causes Gram-negative bacteria to appear pink under Gram staining?

The thin peptidoglycan layer and outer membrane do not retain the stain, so they appear pink after counterstaining.

What is a key difference between bacterial cell walls and archaeal cell walls?

Bacteria typically have peptidoglycan (polysaccharide and polypeptide), whereas archaea use different polysaccharides and proteins in their cell walls.

How do bacteria primarily reproduce?

Asexually through binary fission, producing genetically identical offspring (clones) except for replication errors.

What does binary fission involve?

The parent copies its circular genome, moves the copy to the other side, and the cell splits into two genetically identical daughter cells.

Are bacterial offspring clones?

Yes, most are genetically identical to the parent except for mutations that occur during DNA replication.

What is bacterial generation time and how fast can it be under ideal conditions?

The time for a population to double; some bacteria can double in as little as 20 minutes.

How can short generation time influence mutations in a population?

Mutations occur during replication and can accumulate rapidly; advantageous mutations can quickly rise in frequency.

How can mutations relate to antibiotic resistance?

Mutations that confer resistance can allow individuals to survive antibiotics and be passed on to offspring, increasing resistance in the population.

What are the three mechanisms of bacterial genetic recombination?

Transformation, transduction, and conjugation.

What is transformation in bacteria?

Uptake of DNA from the surrounding environment by a bacterium and incorporation into its genome.

What is transduction?

Transfer of bacterial genes from one bacterium to another via bacteriophages that accidentally package bacterial DNA.

What is conjugation?

Transfer of plasmids from a donor to a recipient bacterium via a pilus (mating bridge), yielding new genetic information.

What is a phage?

A virus that infects bacteria; consists of a capsid enclosing viral DNA or RNA; not considered living by many scientists.

How does transduction lead to new allele combinations?

A phage carrying bacterial DNA injects it into a recipient, where homologous recombination can replace existing alleles with new ones.

What is homologous recombination?

A recombination process where similar sequences exchange segments, producing new allele combinations.

What is the F plasmid and its role in conjugation?

A plasmid that enables transfer during conjugation; donor with F plasmid forms a pilus to transfer the plasmid to a recipient.

What is a pilus in bacterial conjugation?

A bridge-like structure that connects donor and recipient cells to transfer plasmids.

Why is genetic recombination important for bacterial survival?

It generates new allele combinations, helping bacteria adapt to changing environments and resist antimicrobial agents.

What does metabolism refer to in biology?

An organism's use of energy, including how it obtains energy and how it breaks it down.

How can organisms be categorized by metabolism with respect to carbon source?

Autotrophs obtain carbon from inorganic CO2; heterotrophs obtain carbon from organic molecules.

From what carbon source do autotrophs obtain carbon?

Inorganic carbon dioxide (CO2).

From what carbon source do heterotrophs obtain carbon?

Organic molecules from food.

What energy source do photoautotrophs use?

Sunlight.

What energy source do chemoautotrophs (chemolithotrophs) use?

Inorganic chemical energy, such as hydrogen sulfide (H2S).

What process do chemoautotrophs use to build organic molecules from CO2?

Chemosynthesis.

What distinguishes photoheterotrophs in terms of carbon and energy sources?

Energy from sunlight; carbon from inorganic molecules.

What is nitrogen fixation?

Conversion of atmospheric N2 into ammonia (NH3) that can be incorporated into amino acids and nucleic acids.

What are obligate aerobes?

Organisms that must have oxygen to survive.

What are obligate anaerobes?

Organisms that must live in environments with no (or very low) oxygen.

What are facultative anaerobes?

Organisms that can use oxygen when present but can also survive with little or no oxygen by switching to anaerobic respiration.

What are the major differences between archaeal and bacterial metabolism and molecular biology?

Archaea have different ribosome structures; their protein synthesis and DNA replication are more like eukaryotes; their cell membranes differ, contributing to domain separation.

What are methanogens and where are they typically found?

Archaea that generate methane; common in the guts of ruminant animals and help digest cellulose.

What are extremophiles and name three types?

Organisms thriving in extreme conditions; thermophiles (heat), halophiles (high salt), acidophiles (low pH).

What are non-extreme archaea?

Archaea that do not live in extreme conditions.

What are proteobacteria?

A huge, diverse clade of bacteria, many Gram-negative; includes several disease-causing species.

Name disease-causing bacteria mentioned from the proteobacteria group.

Escherichia coli (pathogenic strains), Salmonella, Vibrio cholerae, Helicobacter pylori.

What disease is associated with Vibrio cholerae?

Cholera — a severe diarrheal disease typically spread through contaminated water.

What disease is Helicobacter pylori associated with?

Most stomach ulcers (gastric ulcers).

What are Chlamydias?

A gram-negative clade of intracellular parasites; common sexually transmitted diseases; treatable with antibiotics.

What are Spirochetes and give two examples?

Spiral-shaped bacteria; examples include the agents of syphilis and Lyme disease; treated with antibiotics.

What are cyanobacteria and why are they important?

Gram-negative, photosynthetic bacteria that generate much of Earth's oxygen and are linked to the origin of chloroplasts.

What characterizes gram-positive bacteria and name two notable groups?

A diverse group including Staphylococcus and Streptococcus; also includes actinomycetes, important soil decomposers and antibiotic sources.

What are actinomycetes known for?

Soil-decomposers, responsible for the soil smell, and a major source of antibiotics.

What role do prokaryotes play in environmental nutrient cycling?

They decompose dead matter and release nutrients like nitrogen, phosphorus, potassium, calcium, etc., enabling recycling in ecosystems.

What is symbiotic nitrogen fixation?

Nitrogen-fixing bacteria living in mutualistic relationships with plants (roots) or within animal digestive tracts, supplying bioavailable nitrogen.

Why is nitrogen fixation essential for life on Earth?

It provides bioavailable nitrogen in forms (like ammonia) that can be used to synthesize amino acids and nucleic acids.

How do nitrogen-fixing bacteria contribute to agriculture and ecology?

They supply nitrogen to plants, supporting growth and contributing to ecological nitrogen cycles.

What is the relationship between cyanobacteria and chloroplasts in plants?

Cyanobacteria are ancient photosynthetic bacteria; endosymbiotic events led to chloroplasts in plants and algae.

What is the significance of antibiotic production in actinomycetes?

Actinomycetes are important sources of antibiotics used in medicine.