Chapter 1-7 Microbiology Review: Prokaryotes, Archaea, Bacteria, and Viruses

Flashcards cover key concepts from the lecture notes, including metabolism, prokaryotes, archaea, bacteria, symbiosis, pathogens, and viruses.

What defines an obligate aerobe, and what is its metabolic requirement?

An obligate aerobe is an organism that unequivocally requires oxygen (O2) for survival and growth. These organisms perform aerobic respiration, using O2 as the final electron acceptor in their electron transport chain to generate ATP efficiently. They cannot grow in the absence of oxygen.

What characterizes an obligate anaerobe, and how does it metabolize?

An obligate anaerobe is an organism that cannot tolerate the presence of oxygen (O2) and is often harmed or killed by it. These organisms rely exclusively on anaerobic metabolic pathways, such as anaerobic respiration (using electron acceptors other than O2) or fermentation, to generate energy. They lack the enzymes (e.g., superoxide dismutase, catalase) to detoxify reactive oxygen species.

Describe a facultative anaerobe and its metabolic adaptability.

A facultative anaerobe is an organism capable of growing with or without oxygen (O2). When O2 is present, they typically prefer to perform more efficient aerobic respiration. In the absence of O_2, they switch to less efficient anaerobic respiration or fermentation to produce energy, demonstrating metabolic flexibility to adapt to their environmental conditions.

Where do prokaryotes perform the process of respiration, and what is notable about these structures?

In prokaryotes, respiration occurs on infoldings of the plasma membrane, which are internal extensions of the cell membrane. Unlike eukaryotic cells, prokaryotic cells do not possess membrane-bound organelles with a separate double membrane for respiration (like mitochondria). Therefore, these membrane regions are not considered organelles in the eukaryotic sense.

What are thylakoid membranes in prokaryotes, and what is their function?

Thylakoid membranes in prokaryotes are specialized membrane regions, often appearing as flattened sacs or vesicles, that bear photosynthetic pigments. These structures serve as the primary sites where photosynthesis takes place in photosynthetic bacteria and cyanobacteria, facilitating the capture of light energy.

Which pigment is fundamental to photosynthesis in prokaryotes, and what is its role?

Chlorophyll (or bacteriochlorophyll in some bacteria) is the central pigment for photosynthesis in prokaryotes. Embedded within the thylakoid membranes or plasma membrane, chlorophyll is responsible for absorbing light energy, which is then converted into chemical energy to drive the synthesis of organic compounds.

What are methanogens, and what are their typical habitats?

Methanogens are a group of obligate anaerobic archaea that produce methane (CH_4) as a metabolic byproduct, a process known as methanogenesis. They are commonly found in oxygen-depleted environments such as swamps, marine sediments, the digestive tracts of ruminant animals (e.g., cows), and sewage treatment plants, playing a significant role in the global carbon cycle.

Are Archaea known to be human pathogens, distinguishing them from other microbial groups?

No, most archaea are not known to be pathogenic to humans. This significantly differentiates them from many bacteria, which include numerous human pathogens. While archaea are ubiquitous in various environments, their role in disease is largely unexplored and currently considered negligible.

What is peptidoglycan, and what is its function in bacteria?

Peptidoglycan, also known as murein, is a unique polymer that forms the rigid layer of the bacterial cell wall. It is composed of alternating sugar chains (N-acetylglucosamine, NAG, and N-acetylmuramic acid, NAM) cross-linked by short peptide chains. This mesh-like structure provides structural integrity to the bacterial cell, protecting it from osmotic lysis and maintaining its shape.

How do Gram-positive and Gram-negative bacteria differ in their cellular structure and Gram staining results?

Gram-positive bacteria possess a thick layer of peptidoglycan in their cell wall, located outside the plasma membrane, and lack an outer membrane. This thick peptidoglycan retains the crystal violet stain, causing them to appear purple under a microscope after Gram staining. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer situated between their inner plasma membrane and an outer membrane. The outer membrane, containing lipopolysaccharides (LPS), prevents the crystal violet from being retained, causing them to stain red or pink after counterstaining with safranin.

Name a significant Gram-positive bacterium discussed in lecture that causes disease, highlighting a unique feature.

Mycobacterium tuberculosis is a Gram-positive bacterium that causes tuberculosis. It is notable for having a unique, complex cell wall with a high content of mycolic acid, a waxy lipid, which contributes to its acid-fast staining property and makes it resistant to many antibiotics and host immune defenses, rather than just having a thick peptidoglycan layer.

What is an endospore, which bacterial genera form them, and why are they significant?

An endospore is a highly durable, dormant, and thick-walled resting cell formed by certain Gram-positive bacteria, primarily in the genera Bacillus and Clostridium, when environmental conditions become unfavorable. Endospores are extremely resistant to heat, desiccation, radiation, and chemical disinfectants, allowing the bacteria to survive harsh conditions for extended periods. Their survival capability makes them significant in disease transmission and sterilization challenges.

What disease is caused by Bacillus anthracis, and how do endospores contribute to its pathology?

Bacillus anthracis is the bacterium responsible for anthrax, a severe disease that can manifest in inhalational, cutaneous, and gastrointestinal forms. The highly resistant endospores of B. anthracis are crucial for its persistence in the environment and transmission. Infection typically occurs when endospores are inhaled, ingested, or enter through skin lesions, leading to their germination and subsequent proliferation within the host.

What is a bacteriophage, and why is it important in genetic studies?

A bacteriophage, often simply called a phage, is a type of virus that specifically infects and replicates within bacteria. Bacteriophages consist of a nucleic acid genome (DNA or RNA) encased in a protein shell. They are widely used in teaching labs and research to study viral genomes, replication mechanisms, and genetic manipulation due to their lytic (destroying host cells) and lysogenic (integrating into host genome) cycles.

Define a capsid and explain its composition and function in viruses.

A capsid is a protein shell that encloses and protects the viral genetic material (genome). It is composed of multiple protein subunits called capsomeres, which self-assemble into diverse symmetrical shapes (e.g., helical, icosahedral). The capsid's primary functions include protecting the viral genome from nucleases, facilitating attachment to host cells, and mediating the delivery of the viral genome into the host cell.

What type of genetic material do HIV and many animal viruses utilize, and what unique enzyme is associated with HIV?

HIV (Human Immunodeficiency Virus) and many other animal viruses use RNA as their genetic material. HIV is specifically a retrovirus, meaning it carries an enzyme called reverse transcriptase. This enzyme enables the virus to convert its RNA genome into a DNA copy, which then integrates into the host cell's genome, a critical step in its replication cycle.

Explain the key differences between exotoxins and endotoxins produced by bacteria.

Exotoxins are toxic proteins secreted by living bacteria (both Gram-positive and Gram-negative) into their environment. They are highly potent, often target specific cell types, and are typically heat-labile. Examples include toxins causing botulism, tetanus, and cholera. Endotoxins, on the other hand, are components of the outer membrane of Gram-negative bacteria, specifically the lipid A portion of lipopolysaccharide (LPS). They are released only when bacterial cells die and disintegrate, and they are generally heat-stable. Endotoxins cause a generalized inflammatory response, leading to symptoms like fever, shock, and disseminated intravascular coagulation.

Describe the mutualistic relationship between Rhizobium and plants.

Rhizobium is a genus of soil bacteria that forms a crucial mutualistic symbiotic relationship with legume plants (e.g., soybeans, peas). These bacteria infect the plant roots, leading to the formation of specialized structures called root nodules. Within these nodules, Rhizobium bacteria fix atmospheric nitrogen (N2) into a usable organic form (ammonia, NH3) for the plant, enhancing plant growth. In exchange, the plant provides the bacteria with carbohydrates (carbon compounds) produced through photosynthesis.

What organism causes Lyme disease, and what is its mode of transmission?

Lyme disease is caused by the spirochete bacterium Borrelia burgdorferi. It is a vector-borne disease primarily transmitted to humans through the bite of infected deer ticks (genus Ixodes). The disease is characterized by a distinctive 'bull's-eye' rash (erythema migrans) and can lead to joint pain, neurological problems, and heart issues if left untreated.

What is a heterocyst, and what is its role in specific cyanobacteria?

A heterocyst is a specialized, thick-walled, nitrogen-fixing cell found in certain filamentous cyanobacteria, such as Anabaena. Its primary role is to create an anaerobic environment necessary for the nitrogenase enzyme to function, which is highly sensitive to oxygen. By isolating nitrogen fixation in heterocysts, the cyanobacterium can perform both oxygen-evolving photosynthesis in vegetative cells and oxygen-sensitive nitrogen fixation in a 'division of labor'.

What is Anabaena, and what notable feature does it exhibit?

Anabaena is a genus of filamentous cyanobacteria (also known as blue-green algae) that exhibits a remarkable example of cellular differentiation and division of labor. Its filaments consist of photosynthetic vegetative cells that produce oxygen and specialized heterocysts that are dedicated to nitrogen fixation. This arrangement allows the organism to efficiently carry out two oxygen-sensitive processes (photosynthesis and nitrogen fixation) simultaneously within its colonial structure.

Provide a mutualistic example of plant-microbe symbiosis discussed in the notes, detailing the benefits for each partner.

A prime example of plant-microbe mutualism is the symbiotic relationship between Rhizobium bacteria and legume plants, such as soybeans. In this interaction, Rhizobium bacteria reside in root nodules and convert atmospheric nitrogen (N_2) into a biologically available form (nitrogen fixation) for the plant, critical for protein and nucleic acid synthesis. In return, the plant supplies the bacteria with carbohydrates derived from photosynthesis, providing an energy source for the bacteria. Both organisms benefit from this interdependence.