Microbial Diversity, Evolution, Systematics, Cell Biology, and Basic Parasitology

Flashcard set covering microbial diversity, origin of life models, taxonomy, domain features, cellular structure, viral classification, and basic parasitology concepts.

What did the Miller-Urey experiment of 1953 demonstrate regarding the origin of life?

It demonstrated that organic molecules, specifically amino acids, can form from inorganic precursors under simulated early Earth conditions.

According to the RNA World Hypothesis, why is RNA considered central to early life before DNA and proteins evolved?

RNA can perform a dual role: it can carry genetic information and fold into complex structures that catalyze chemical reactions as a ribozyme.

What is a protocell (or probiont)?

A hypothetical pre-cellular structure in which biological molecules were enclosed within a lipid-like membrane boundary.

Which four integrated systems must a protocell possess to be considered fully alive?

Heredity, metabolism, growth, and reproduction.

According to the Endosymbiotic Theory, from which specific ancestral bacterial lineages did mitochondria and chloroplasts evolve?

Mitochondria evolved from engulfed aerobic Proteobacteria, while chloroplasts evolved from engulfed photosynthetic Cyanobacteria.

How do membrane lipids in Archaea differ chemically from those in Bacteria and Eukarya?

Archaea have ether-linked membrane lipids with phytanyl (isoprenoid) sidechains, whereas Bacteria and Eukarya have ester-linked membrane lipids with fatty acid chains.

What are the three main processes of Horizontal Gene Transfer (HGT) in prokaryotes?

1. Transformation: uptake of naked extracellular DNA from the environment.
2. Transduction: transfer of DNA mediated by bacteriophages.
3. Conjugation: direct cell-to-cell transfer of DNA (often plasmids) via a pilus.

What are the three primary approaches used in microbial taxonomy?

1. Phenotypic Classification: based on observable traits.
2. Genotypic Classification: based on genetic information.
3. Polyphasic Taxonomy: an integrated modern approach combining phenotypic, genotypic, and phylogenetic evidence.

How did Carl Woese's ribosomal RNA analysis alter the classification of living organisms?

By comparing small-subunit (16S) rRNA sequences, Carl Woese revealed that prokaryotes belong to two distinct evolutionary groups (Bacteria and Archaea), establishing the three-domain system.

How do ICNP and SeqCode differ in prokaryotic nomenclature?

The International Code of Nomenclature of Procaryotes (ICNP) governs the formal naming of Bacteria and Archaea using viable pure cultures, whereas SeqCode accepts DNA sequence data to name uncultivated microbes.

What is the correct hierarchical order of major taxonomic ranks for cellular organisms?

Domain $\rightarrow$ Phylum $\rightarrow$ Class $\rightarrow$ Order $\rightarrow$ Family $\rightarrow$ Genus $\rightarrow$ Species (with strain designations below species level).

What basis does the Baltimore System use to classify viruses?

It categorizes viruses into seven groups based on their genome type (dsDNA, ssDNA, dsRNA, (+)ssRNA, (-)ssRNA, ssRNA-RT, dsDNA-RT) and their strategy for producing messenger RNA (mRNA).

What structural differences distinguish Gram-positive bacterial cell walls from Gram-negative cell walls?

Gram-positive cells have a thick peptidoglycan layer and no outer membrane. Gram-negative cells have a thin peptidoglycan layer inside a periplasmic space and an outer membrane containing lipopolysaccharides and porins.

What common cellular arrangements can spherical bacteria (cocci) form?

Single coccus, diplococci (pairs), streptococci (chains), tetrads (groups of 4), sarcinae (cubical packets of 8), and staphylococci (irregular grape-like clusters).

What is pleomorphism in bacteria?

The ability of bacterial cells to vary in shape or size, which can result from a lack of a rigid cell wall (e.g., Mycoplasma), culture age, nutrient conditions, or cell-wall damage.

How do capsules and slime layers differ within the bacterial glycocalyx?

A capsule is well-defined, organized, firmly bound to the cell surface, and difficult to remove. A slime layer is diffuse, unorganized, loosely attached, and easily washed away.

What is an endospore, and what is its biological purpose?

An endospore is a dormant, non-reproductive, and highly resistant survival structure formed inside certain bacteria (e.g., Bacillus, Clostridium) to protect genetic material during extreme environmental conditions.

What chemical complexes in the endospore core contribute to its extreme heat resistance?

Calcium-dipicolinic acid ($\text{Ca}^{2+}\text{-DPA}$) complexes.

How do bacterial flagella and archaeal archaella differ in structure, assembly, and energy source?

Bacterial flagella are hollow, made of flagellin, assemble at the tip, and are powered by a proton or sodium ion gradient. Archaeal archaella are solid, thinner, made of archaellin, assemble at the base, and are powered by ATP.

What are the six general stages of biofilm development?

1. Surface conditioning
2. Reversible attachment
3. Irreversible attachment
4. Microcolony formation
5. Maturation (3D community with water channels)
6. Dispersion

What is the distinction between a definitive host and an intermediate host in parasitology?

A definitive host is where the parasite undergoes sexual reproduction or matures into an adult form. An intermediate host supports larval development, asexual reproduction, or immature stages.

What is the difference between an infective stage and a diagnostic stage of a parasite?

The infective stage is the form capable of entering a host and initiating infection. The diagnostic stage is the form or evidence detected in a specimen to confirm infection in the laboratory.

How do prions propagate without nucleic acids?

Prions propagate through templated misfolding: the infectious abnormal protein ($PrP^{Sc}$) binds to the normal host protein ($PrP^C$) and induces it to alter its conformation into the abnormal form.

What are viroids, and how do they differ from viruses?

Viroids are small, infectious, circular single-stranded RNA molecules that infect plants; unlike viruses, they completely lack a protein capsid and lipid envelope.

What are the five steps of the lytic cycle in bacteriophages?

1. Attachment (binding to specific host receptors)
2. Penetration (injection of viral nucleic acid)
3. Biosynthesis (synthesis of phage DNA and proteins)
4. Assembly/maturation (packaging new phages)
5. Lysis and release (host cell destruction and release of progeny)