Introduction to Cell and Molecular Biology, Chemical Organization, and the Cytosol

Vocabulary practice flashcards covering cell biology fundamentals, historical cytology discoveries, chemical organization of macromolecules and bioelements, water properties, and the structural composition of the cytosol and cytoskeleton.

Cell and Molecular Biology

The branch of biological sciences that studies the structure and functions of the cell as a fundamental unit of living organisms, integrating morphology from light microscopy, ultrastructure from electron microscopy, and molecular structure-function relationships.

First Compound Microscope

An optical magnification device consisting of two aligned lenses mounted in telescoping draw-tubes, constructed circa 1595 by Zacharias Jansen.

Robert Hooke

English natural philosopher (1635–1703) who published Micrographia in 1665, observing sliced cork at $450\times$ magnification and introducing the terms cella (room) and cellula (small room).

Antony van Leeuwenhoek

Dutch microscopist (1632–1723) who constructed high-power single-lens microscopes and became the first to observe live cells, including protozoa, bacteria, erythrocytes, and spermatozoa.

Robert Brown

Scottish botanist who formulated the first biological generalization in 1831 by discovering that the nucleus is a constant and universal cellular component.

Protoplasm Concept

A foundational cellular generalization describing the cell as a mass of living matter termed protoplasm bounded externally by the plasmalemma (cell membrane).

Cellular Theory (1839)

A biological theory formulated by Matthias Schleiden and Theodor Schwann stating that all living organisms consist of cells and their products, cells maintain independent life, and cellular activity is subordinated to the whole organism.

Omnis cellula e cellula

A Latin axiom popularized by Rudolf Virchow stating that all existing cells arise exclusively from the division of pre-existing cells.

Rudolf Virchow

German pathologist (1821–1902) who established cellular pathology and histopathology by detailing the microscopic cellular alterations underlying human disease in Cellular Pathology.

Freeze Fracturing

A preparation technique for electron microscopy where specimens frozen in ice are fractured along hydrophobic interior membrane planes and etched via sublimation to expose ultrastructural surface details.

Differential Centrifugation

A preparative method for isolating cell organelles by progressive centrifugal acceleration: whole cells and nuclei sediment at $600 \times g$, mitochondria/lysosomes/peroxisomes at $15\,000 \times g$, microsomes at $100\,000 \times g$, and ribosomes/viruses at $300\,000 \times g$.

George Emil Palade

Romanian-American cell biologist awarded the 1974 Nobel Prize in Physiology or Medicine (shared with Albert Claude and Christian de Duve) for discovering ribosomes, characterizing mitochondrial cristae, and describing the intracellular protein secretory pathway.

Victor Babeș

Romanian bacteriologist (1854–1926) who established passive immunization (serotherapy), discovered Babesia, identified Babeș-Negri rabies corpuscles and Babeș-Ernst diphtheria bodies, formulated antibiosis, and co-authored the first microbiology treatise in 1886.

Law of Volume Constancy

The biological principle stating that differentiated cells from a given organ share comparable volumes across different animal species regardless of total body mass; differences in organ volume result from cell count rather than individual cell size.

Macroelements

The four fundamental cellular elements—carbon ($\text{C}$), hydrogen ($\text{H}$), oxygen ($\text{O}$), and nitrogen ($\text{N}$)—that each constitute between $2\%$ and $60\%$ of cellular mass.

Microelements

Less abundant elements representing $0.02\text{--}0.1\%$ each of cellular mass, comprising metalloids ($\text{P}$, $\text{S}$, $\text{Cl}$) and metal ions ($\text{Na}$, $\text{K}$, $\text{Ca}$, $\text{Mg}$).

Oligoelements

Trace chemical elements found at levels under $0.02\%$ each in cells, including iron ($\text{Fe}$), cobalt ($\text{Co}$), zinc ($\text{Zn}$), iodine ($\text{I}$), selenium ($\text{Se}$), and fluorine ($\text{F}$), that fulfill catalytic or prosthetic functions.

Electric Dipole of Water

The polar molecular geometry of $\text{H}_2\text{O}$ characterized by a bond angle of $104.45^\circ$, an $\text{O-H}$ distance of $95.84\,\text{pm}$, and an asymmetric charge distribution that confers a high dielectric constant and universal solvent capacity.

Aquaporin-1 (AQP1)

A tetrameric integral membrane channel protein composed of six transmembrane helical segments per subunit that facilitates selective, bidirectional osmotic water transport across the plasma membrane.

Glycogen

The principal storage polysaccharide in animal hepatocytes and muscle cells, formed by branched polymers of glucose featuring linear $\alpha\text{-1,4-glycosidic}$ bonds and $\alpha\text{-1,6-glycosidic}$ branch linkages.

Proteoglycan Aggregates

Extracellular matrix complexes formed by a central filament of hyaluronic acid linked non-covalently via link proteins to core proteins bearing glycosaminoglycan side chains such as chondroitin sulfate and keratan sulfate.

Phospholipids

Amphipathic membrane structural lipids possessing a hydrophilic polar head group (phosphate esterified to amino alcohols or polyols) and two nonpolar hydrophobic fatty acid tails esterified to a glycerol backbone.

Sphingomyelin

A sphingophospholipid abundant in animal myelin sheaths composed of a sphingosine backbone linked to a fatty acid by an amide bond and esterified to phosphorylcholine.

Selenocysteine

The 21st proteinogenic amino acid, structurally corresponding to a cysteine derivative in which a selenium atom replaces the standard sulfur atom of the thiol group.

Nucleoside vs. Nucleotide

A nucleoside is a molecular unit consisting of a nitrogenous purine or pyrimidine base linked to a pentose sugar; a nucleotide is a nucleoside phosphorylated by one to three phosphate groups.

Cytosol

The liquid, non-organellar portion of the cytoplasm (hyaloplasm or cytoplasmic matrix) containing dissolved macromolecules, enzymes, and cytoskeleton elements that displays colloidal behaviors such as diffusion, Brownian motion, and sol-gel transitions.

Myosin II

A conventional motor protein dimer consisting of two heavy chains and four light chains, featuring two globular amino-terminal ATPase heads and a long coiled-coil tail that assemble into thick bipolar filaments with a central bare zone of $300\,\text{nm}$.

Light Meromyosin and Heavy Meromyosin

Proteolytic fragments of myosin II produced by trypsin digestion; light meromyosin (LMM, $110\,\text{nm}$) forms the assembly tail, while heavy meromyosin (HMM, $45\,\text{nm}$) contains the hinge neck and catalytic head domains.

G-Actin and F-Actin

Monomeric globular actin (G-actin) that binds $\text{ATP}$ and polymerizes into polarized filamentous strands (F-actin), forming thin filaments in striated muscle and microfilaments ($7\,\text{nm}$ diameter) in non-muscle cells.

Troponin Complex

A heterotrimeric calcium-sensitive regulatory complex on thin filaments consisting of Troponin T (TnT, anchoring to tropomyosin), Troponin C (TnC, binding $\text{Ca}^{2+}$), and Troponin I (TnI, inhibiting actin-myosin cross-bridging).

Cytochalasin D

A fungal alkaloid that caps the barbed (+) ends of microfilaments, inhibiting actin monomer addition and halting cellular motility, cytokinesis, and filament elongation.

Phalloidin

A bicyclic toxic peptide from the death cap mushroom Amanita phalloides that locks neighboring subunits of F-actin together, preventing microfilament depolymerization.

Intermediate Filaments

Apolar, mechanically tensile cytoskeletal fibers ($8\text{--}10\,\text{nm}$ diameter) assembled from parallel coiled-coil dimers forming antiparallel, staggered tetramers, which pack into protofilaments and protofibrils.

Desmin Filaments

Class III intermediate filament proteins found in skeletal, cardiac, and smooth muscle cells whose diagnostic antibody labeling allows clinical detection of rhabdomyosarcomas.

Microtubules

Hollow, cylindrical cytoskeletal structures with an outer diameter of $24\text{--}25\,\text{nm}$ consisting of 13 parallel protofilaments built of alternating $\alpha$-tubulin and $\beta$-tubulin heterodimers bound to guanosine nucleotides.

Centrosome

The primary animal microtubule organizing center (MTOC) consisting of an amorphous pericentriolar matrix and two orthogonally oriented centrioles, each containing nine peripheral triplets ($9\times 3$) of microtubules.

Axoneme

The core motorized shaft of eukaryotic cilia and flagella containing an arrangement of nine peripheral doublet microtubules and two central singlet microtubules ($9+2$ architecture) connected by radial spokes, dynein arms, and nexin bridges.

Colchicine

An alkaloid derived from Colchicum autumnale (autumn crocus) that binds free tubulin heterodimers to inhibit microtubule polymerization and block mitotic spindle assembly.

Taxol

A chemotherapeutic diterpenoid extracted from the bark of Taxus baccata (yew tree) that binds along assembled microtubules to stimulate polymerization, prevent depolymerization, and arrest cell cycle progression.

Vinblastine and Vincristine

Vinca alkaloids from Vinca sp. that disrupt microtubule dynamics by suppressing polymerization at high concentrations while promoting tubulin assembly at low concentrations.