Microbiology Comprehensive Review: Cell Biology, Metabolism, Genetics, Virology, and Antimicrobials

Practice flashcards testing core microbiology concepts from lecture slides and transcripts, covering cell morphology, cell wall architecture, bacterial metabolism, culture techniques, gene regulation, horizontal gene transfer, virology, and antimicrobial control methods.

What are the three primary metabolic pathways used by bacteria and their respective ATP yields?

Aerobic respiration yields $38\,\text{ATP}$, anaerobic respiration yields $4\text{--}36\,\text{ATP}$, and fermentation yields $4\,\text{ATP}$.

What two chemical components make up the repeating disaccharide backbone of peptidoglycan, and what type of bond links them?

N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), linked together by glycosidic bonds.

Identify the three flagellar arrangements shown in images (a), (b), and (c).

(a) Peritrichous (flagella distributed all over the cell surface), (b) Polar (a single flagellum at one pole), and (c) Lophotrichous (a cluster/tuft of flagella at one pole).

What are the major structural differences in peptidoglycan and cell wall composition between Gram (-) and Gram (+) bacteria as outlined in this summary table?

Gram (-) cells have $1\text{--}3$ peptidoglycan sheets, few crosslinks, and lipoproteins linking to an outer membrane. Gram (+) cells have $10\text{--}15$ peptidoglycan sheets, many crosslinks, and teichoic acids and lipoteichoic acids.

What are the three distinct regions of Lipopolysaccharide (LPS), and which part functions as the endotoxin?

The three regions are the O-specific polysaccharide (O-antigen), Core polysaccharide, and Lipid A. The Lipid A portion is embedded in the outer membrane and acts as the endotoxin.

What is the structural composition and function of teichoic acids in Gram-positive bacterial cell walls?

They are polymers of repeating ribitol or glycerol phosphate that create an overall negative surface charge and assist in binding positively charged ions prior to transport. When covalently attached to membrane lipids, they are called lipoteichoic acids.

How does Twitching motility occur in bacteria?

Type IV pili extend outward, their tip adhesins attach to a surface, and subsequent pilus retraction pulls the cell forward.

What drives the rotation of the bacterial flagellum motor?

The proton motive force, which is converted into rotation by Mot proteins located in the stator surrounding the rotor rings in the basal body.

Based on the diagram, how do the apoenzyme, cofactor, and holoenzyme relate to one another?

An inactive apoenzyme (protein portion) combines with an activator cofactor or coenzyme (nonprotein portion) to assemble the fully active holoenzyme.

What is allosteric inhibition, and how does it affect enzyme function?

A noncompetitive inhibitor binds to an allosteric site (a site distinct from the active site), altering the three-dimensional shape of the active site so that the substrate cannot bind effectively.

What are the preferred temperature ranges for psychrophiles, mesophiles, thermophiles, and hyperthermophiles?

Psychrophiles prefer cold temperatures; mesophiles prefer moderate temperatures ($25\text{--}40^\circ\text{C}$, optimal around $37^\circ\text{C}$); thermophiles prefer heat ($50\text{--}60^\circ\text{C}$); and hyperthermophiles have an optimum growth temperature of $80^\circ\text{C}$ or higher.

What is the difference between a chemically defined medium and a complex medium?

A chemically defined medium has a precisely known chemical composition of pure ingredients, whereas a complex medium contains nutrient-rich extracts of yeasts, meat, or plants where the exact chemical composition varies.

In comparative genomics, what is the distinction between the core genome and the pan genome?

The core genome consists of all genes shared in common among all strains being compared, while the pan genome is the sum of all genes across all compared strains.

Under what specific conditions of glucose and lactose is transcription of the lac operon turned on?

Transcription is turned on only when lactose is present AND glucose is absent.

How does cyclic AMP (cAMP) regulate catabolite repression in the lac operon?

When glucose levels are high, cAMP levels are low. When glucose is exhausted, cAMP concentration increases, enabling cAMP to bind its activator protein and stimulate transcription of operons for alternative carbon sources.

What are the three types of base-pair substitution point mutations, and what are their effects on the encoded protein?

Missense mutations change the encoded amino acid; nonsense mutations change a codon into an early stop codon resulting in a truncated protein; and silent mutations alter the codon without changing the encoded amino acid.

Why is homologous recombination necessary for horizontal gene transfer to stably alter a recipient bacterium?

Transferred linear donor DNA fragments lack an origin of replication; without homologous recombination into the host chromosome, the incoming DNA cannot replicate and is eventually lost during cell divisions.

What defines a prophage, a lysogen, and the process of induction?

A prophage is viral DNA integrated into the bacterial chromosome; a lysogen is a bacterial cell harboring a prophage; and induction is the excision of the prophage from the host chromosome into the lytic cycle, often triggered by stress.

How does specialized transduction occur during lambda phage induction?

Due to incorrect excision from the host chromosome, a portion of adjacent donor bacterial genes (such as galactose genes) replaces part of the phage genome, resulting in defective progeny phages that all carry that specific donor gene.

According to this comparison table, what DNA is transferred during conjugation by an $F^+$ donor versus an Hfr donor?

An $F^+$ donor transfers F plasmid only, whereas an Hfr donor transfers partial F plasmid DNA along with a segment of chromosomal donor DNA.

What is the primary difference in translation potential between positive (+) single-stranded RNA and negative (-) single-stranded RNA viral genomes?

Positive (+) strand RNA can be directly translated into viral proteins by host ribosomes, whereas negative (-) strand RNA cannot be translated directly and requires a viral RNA-dependent RNA polymerase to synthesize a readable positive strand.

How does the antiviral drug Remdesivir inhibit SARS-CoV-2 replication?

It acts as a modified nucleotide analog that targets and inhibits the viral RNA-dependent RNA polymerase enzyme.

What is the difference between antigenic drift and antigenic shift in Influenza virus?

Antigenic drift is the accumulation of random point mutations in viral surface genes leading to new strains, while antigenic shift is the reassortment/shuffling of entire RNA genome segments when multiple viruses infect a single host, generating novel subtypes.

Which viral proteins in Human Papilloma Virus (HPV) stimulate uncontrolled epithelial proliferation and warts?

The early proteins E6 and E7, which interfere with normal cell cycle arrest and inhibit apoptosis (programmed cell death).

What are the essential steps of HIV replication within a target host cell?

Viral gp120 binds the host CD4 receptor; membranes fuse and the capsid uncoats; (+) ssRNA is reverse transcribed into cDNA by reverse transcriptase; dsDNA is integrated into the host genome by integrase; viral RNA and proteins are produced; and new virions assemble and bud from the plasma membrane.

What are the standard operational parameters for an autoclave to achieve complete sterilization?

$121^\circ\text{C}$ for at least $15\,\text{minutes}$, killing all vegetative cells and endospores.

How do bacteriostatic, bactericidal, and bacteriolytic antimicrobial agents differ in their effects on total and viable cell counts?

Bacteriostatic agents halt growth without decreasing viable or total counts; bactericidal agents kill cells so viable count declines while intact dead cells maintain total count; and bacteriolytic agents lyse cells so both viable and total cell counts decline rapidly.

According to the antimicrobial resistance gradient, place bacterial spores, mycobacteria, vegetative bacteria, and enveloped viruses in order from most resistant to least resistant.

Most resistant: Bacterial spores > Mycobacteria > Vegetative bacteria > Enveloped viruses (least resistant).

What is the Minimum Inhibitory Concentration (MIC) in this tube dilution assay?

$8\,\mu\text{g/ml}$, because it is the lowest antibiotic concentration where no visible turbidity/growth appears.

What clinical test uses an in vivo delayed-type hypersensitivity reaction to a purified protein extract to detect current or previous infection with Mycobacterium tuberculosis?

The Mantoux skin test.