Cytology: Cell Biology, Microorganisms, Viruses, and Chemical Composition

Comprehensive vocabulary flashcards covering the cytology lecture notes, including cell theory, prokaryotic and eukaryotic cell anatomy, microscopy methods, microbial and viral lifecycles, prions, and elemental chemistry.

Cytology (Cell Biology)

The scientific discipline that studies cells and their organelles, the internal life processes occurring within them, and the mechanisms supporting their survival.

Cell Theory

A foundational biological framework proposed by Schleiden and Schwann (1838) based on three principles: all living organisms consist of one or more cells, the cell is the elementary unit of life, and all cells arise from pre-existing, living cells.

Apoptosis

A genetically programmed, normal physiological process of cell death wherein the cell shrinks, chromatin condenses, budding occurs, and apoptotic bodies are phagocytosed without provoking inflammation.

Necrosis

Premature cell death caused by injury in which the cell swells, becomes leaky, develops blebs, and undergoes cellular and nuclear lysis that triggers inflammation.

Compound Light Microscope

An optical instrument providing a magnifying power of $1000\times$ to $2000\times$ with a resolution limit of $0.2\text{ to }0.5\,\mu\text{m}$ used to observe living or dead, stained or unstained cells.

Transmission Electron Microscope (TEM)

An electron microscope used to observe cellular ultrastructure, offering magnification up to $10{,}000{,}000\times$ with a resolution limit of $0.2\,\text{nm}$.

Scanning Electron Microscope (SEM)

An electron microscope utilized for cell imaging that achieves magnification up to $10{,}000{,}000\times$ with a resolution limit of $3\,\text{nm}$.

Cell Fractionation

A functional laboratory method comprising cell lysis followed by differential centrifugation to isolate specific organelles for biochemical analysis.

Autoradiography

A functional visualization method in which a radioactive precursor is incorporated into cells and its localization or kinetics is recorded via radiography.

Prokaryotes

Unicellular microorganisms lacking internal compartments or membrane-bound organelles whose genetic material consists of a single circular, double-stranded DNA molecule located in the cytoplasm.

Archaea (Archaebacteria)

A domain of prokaryotes that diverged early in life's history, often inhabiting extreme environments (e.g., bogs, sewage farms, ocean depths), and containing no known pathogenic species.

Methanogens

Strictly anaerobic archaea residing in swamps and ruminant or human digestive tracts that convert $\text{CO}_2$ and $\text{H}_2$ gases into methane.

Halophiles

Aerobic archaea that survive and proliferate in extremely high-salinity environments.

Thermophiles

Anaerobic archaea that inhabit hot, sulphurous, and acidic waters; thermoacidophilic chemotrophs grow under acidic conditions and release sulphuric acid.

Thiomargarita namibiensis

One of the largest known bacterial species, possessing a diameter ranging from $100\text{--}300\,\mu\text{m}$.

Pleomorphic Bacteria

Bacteria that modify their morphology in response to changing environmental conditions (e.g., Corynebacterium, Rhizobium), unlike monomorphic bacteria that maintain a single shape.

Binary Fission

An asexual reproduction mechanism common in bacteria whereby a parent cell divides into two equal daughter cells.

Chemotrophic Bacteria

Bacteria that capture free energy via the breakdown of chemical compounds, comprising chemolithotrophs (utilizing inorganic compounds) and chemoorganotrophs (utilizing organic compounds).

Phototrophic Bacteria

Bacteria that obtain free energy from sunlight, classified as photolithotrophs if growing in a mineral milieu or photoorganotrophs if organic compounds are required.

Nucleoid (Nuclear Area)

The electron-dense cytoplasmic region in bacteria, devoid of a nuclear membrane or nucleoli, containing the single circular, double-stranded bacterial chromosome ($75\times 10^4\text{ to }5\times 10^6\,\text{bp}$).

Peptidoglycan (Murein)

A cell wall macromolecule consisting of repeating disaccharides of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) connected by $\beta(1\rightarrow 4)$ glycosidic linkages and cross-linked by polypeptide chains.

Gram-Positive Cell Wall

A homogeneous, rigid bacterial envelope comprising a thick single layer ($15\text{ to }80\,\text{nm}$) of peptidoglycan interlinked with teichoic acids that retains crystal violet dye during Gram staining.

Gram-Negative Cell Wall

A heterogeneous bacterial cell wall composed of a thin peptidoglycan layer ($8\text{ to }12\,\text{nm}$) located in the periplasm and an outer membrane rich in lipopolysaccharides (LPS), lipoproteins, phospholipids, and porins, staining pink in Gram staining.

Capsule

An organized, polysaccharide- or polypeptide-rich layer firmly bound to the bacterial cell wall that acts as a major virulence factor by impeding phagocytosis and promoting surface adherence.

Bacterial Flagellum

A filamentous motility structure consisting of an external filament composed of globular flagellin protein subunits, a hook, and a basal body with protein rings anchoring it to the wall and membrane.

Mesosomes

Irregular plasma membrane invaginations observed in bacteria under electron microscopy that participate in chromosome attachment, DNA replication, and exoenzyme secretion.

Plasmids

Small, circular, double-stranded extra-chromosomal DNA molecules carrying non-essential genes ($5\text{ to }100$ genes) that replicate independently and frequently mediate antibiotic resistance.

Pili (Fimbriae)

Short, rigid, hair-like membrane appendages used by bacteria for attachment to substrates and for cell-to-cell bridging during conjugation.

Sporulation (Sporogenesis)

The multi-hour process of endospore formation within a vegetative parent cell (e.g., in Clostridium or Bacillus) triggered by environmental stressors such as heat or nutrient depletion.

Bacterial Conjugation

The transfer of genetic material (plasmid) between bacterial cells via direct physical contact or through a specialized cytoplasmic bridge.

Mycoplasma (PPLO)

The smallest and simplest known bacteria ($\le 0.3\,\mu\text{m}$ diameter), lacking a cell wall, containing cholesterol in their plasma membrane, and possessing a genome with fewer than 750 genes.

Endosymbiotic Theory

The evolutionary model proposing that eukaryotic organelles originated from prokaryotic endosymbionts, specifically that aerobic bacteria gave rise to mitochondria and cyanobacteria gave rise to chloroplasts.

Cytosol

The viscous, gel-like intracellular fluid supported by the cytoskeleton where the majority of cellular metabolic reactions proceed and where ribosomes and proteasomes are suspended.

Endomembrane System

An integrated set of internal eukaryotic membrane-bound structures—including the endoplasmic reticulum, Golgi apparatus, and lysosomes—that mediates the synthesis, transport, sorting, and degradation of biomolecules.

Plasmodesmata

Microscopic cytoplasmic channels spanning plant cell walls that allow direct intercellular communication and molecular transport between adjacent cells.

Tonoplast

The selective bounding membrane that delimits the central vacuolar compartment in eukaryotic plant cells.

Capsid

The protective viral protein coat assembled from capsomeres that encloses the viral genome, facilitates transmission, and binds to receptor molecules on host cell membranes.

Nucleocapsid

The core macromolecular complex formed by the direct association between viral nucleic acid and capsid proteins.

Lytic Cycle

A viral infectious pathway consisting of attachment, penetration, viral DNA replication and protein synthesis, virion assembly, and host cell lysis to release new viral particles.

Provirus (Lysogenic Cycle)

A latent viral genome integrated into the host cell's chromosomal DNA that replicates passively along with the host chromosome without causing immediate cell death.

Prion

A proteinaceous infectious agent composed of an abnormally folded protein that induces normal host PrP proteins to misfold into the pathological conformation, causing progressive neurodegenerative damage.

Macro-elements (Major Elements)

The essential chemical constituents making up $99\%$ of cellular matter, classified into primary elements ($96\%$: O, C, H, N) and secondary elements ($4\%$: P, Ca, S, Cl, Na, K, Mg).

Oligo-elements (Minor Elements)

Trace chemical elements (B, F, Mn, Fe, Co, Cu, Zn, Se, I, Mo) representing approximately $1\%$ of living matter that play indispensable catalytic roles in biochemical pathways.

Peptide Bond

The covalent amide linkage formed head-to-tail between the carboxylic acid group ($\text{COOH}$) of one amino acid and the amino group ($\text{NH}_2$) of an adjacent amino acid in a polypeptide chain.