Microbiology, Bacterial Ultrastructure, Genetics, Antimicrobials, Pathogenesis, and Immunology

Flashcards on microbiology, cell ultrastructure, bacterial genetics, antimicrobial agents, pathogenesis, and immunology grounded strictly in the lecture notes.

Microbiology

The study of microorganisms, a large and diverse group of microscopic organisms that exist as single cells or cell clusters, as well as non-cellular microscopic entities like viruses.

Prokaryotic Cell

A type of cell lacking a true nucleus and membrane-bound organelles, typically $1-10\,\mu\text{m}$ in size, possessing circular dsDNA, $70\text{S}$ ribosomes, and carrying out cellular respiration in its cell membrane.

Eukaryotic Cell

A cell containing a true nucleus enclosed by a nuclear envelope, typically $10-100\,\mu\text{m}$ in size, possessing linear DNA with histone proteins, $80\text{S}$ ribosomes, and carrying out cellular respiration in mitochondria.

Capsid

A protein coat enclosing the viral nucleic acid (DNA or RNA) that protects the genome and facilitates host cell attachment and penetration.

Viroid

A small, single-stranded, covalently closed circular RNA molecule lacking a protein coat (naked RNA) that functions as an obligate intracellular plant pathogen.

Prion

A transmissible proteinaceous infectious agent devoid of DNA or RNA that causes central nervous system degenerative diseases such as scrapie, Kuru, and Creutzfeldt-Jakob Disease.

Gram Stain

A differential staining procedure devised by Hans Christian Gram using crystal violet, Gram's iodine, $95\%$ ethyl alcohol, and safranin to categorize bacteria based on cell wall properties.

Peptidoglycan

A complex cell wall polymer composed of an alternating backbone of $N\text{-acetylglucosamine}$ (NAG) and $N\text{-acetylmuramic acid}$ (NAM) linked by $\beta 1 \rightarrow 4$ bonds, cross-linked by tetrapeptide side chains.

Capsule

A condensed, well-defined extracellular polysaccharide layer surrounding Gram-positive and Gram-negative bacteria that excludes particles such as India ink and protects against phagocytosis.

Lipopolysaccharide (LPS)

An endotoxin component found exclusively in the outer leaflet of Gram-negative bacterial outer membranes, composed of toxic Lipid A and immunogenic polysaccharide.

Periplasmic Space

A gel-filled space situated between the cell membrane and peptidoglycan in Gram-positive bacteria, or between the inner and outer membranes in Gram-negative bacteria, containing degradative and binding proteins.

Mycolic Acid

Waxy, long-chain fatty acids present in acid-fast bacterial cell walls, such as Mycobacterium tuberculosis, conferring marked resistance to drying, detergents, and strong acids.

Protoplast

A spherical body produced when a Gram-positive bacterium completely loses its cell wall through enzymatic hydrolysis (e.g., lysozyme) or cell wall synthesis inhibition.

Spheroplast

A spherical bacterial structure formed from a Gram-negative bacterium upon partial cell wall loss, which retains its outer membrane.

Pili

Rigid, surface appendages composed of pilin protein subunits; ordinary pili facilitate surface adherence via adhesins, while sex pili mediate donor-recipient attachment in bacterial conjugation.

Endospores

Highly resistant resting cells produced by specific Gram-positive genera (Bacillus, Clostridium, Coxiella) containing a keratin coat and calcium dipicolinate to survive heat, chemicals, and desiccation.

Lag Phase

The initial phase of bacterial growth with a growth rate of zero, during which cells adapt to new environmental conditions and replenish depleted metabolites.

Log Phase

The steady-state phase of bacterial growth characterized by constant logarithmic cell multiplication where cellular mass increases exponentially.

Stationary Phase

A phase in the bacterial growth curve where nutrient depletion or toxic product accumulation halts growth, resulting in a net growth rate of zero as cell death equals cell division.

Sterilization

The complete destruction or removal of all viable microorganisms, including bacterial endospores, from a surface or product.

DNA Gyrase

A Type 2 topoisomerase enzyme in bacteria that relieves supercoiling ahead of the replication fork and serves as the primary target for fluoroquinolone antibiotics.

Missense Mutation

A base substitution in DNA that replaces one amino acid with a different amino acid in the resulting polypeptide chain.

Nonsense Mutation

A base substitution that converts an amino acid-encoding codon into a premature stop codon ($\text{UAG}$, $\text{UGA}$, or $\text{UAA}$), producing a nonfunctional protein.

Transformation

A mode of horizontal gene transfer where a competent recipient bacterial cell takes up naked or free extracellular DNA from its surrounding environment.

Conjugation

Direct cell-to-cell transfer of genetic material involving an F plasmid, mediated by sex pili in Gram-negative bacteria or pheromones in Gram-positive bacteria.

Transduction

The transfer of bacterial DNA from one host cell to another mediated by a viral vector known as a bacteriophage.

Virulence

The quantitative expression or measurement of an infectious agent's capacity to cause disease in a host.

Exotoxin

A soluble, heat-labile polypeptide protein secreted by living Gram-positive or Gram-negative bacteria that possesses high toxicity and immunogenicity.

IgG

The most abundant serum immunoglobulin ($75\%$) with the longest half-life, capable of crossing the placental barrier and dominating secondary humoral immune responses.

IgA

An immunoglobulin existing as a monomer in serum and a dimer in mucosal secretions, serving as the principal barrier against pathogen attachment on epithelial surfaces.

IgM

A large pentameric macroglobulin with 10 antigen-binding sites, serving as the earliest antibody class produced during a primary immune response.

MHC Class I

Molecules expressed on all nucleated cells that present endogenously synthesized cytosolic peptide fragments to $\text{CD8}^+$ cytotoxic T cells.

MHC Class II

Molecules expressed on professional antigen-presenting cells that process and present exogenous vesicular antigens to $\text{CD4}^+$ helper T cells.