Introductory Cytology and Cell Biology

Vocabulary practice flashcards covering cell structure, organelles, junctional complexes, and membrane dynamics from introductory cytology lecture notes.

Cytology

The study of the cell, entailing the investigation of cell components and their respective functions.

Cell

The basic functional and structural unit of an organism that possesses the ability to replicate and create energy from inanimate matter.

Unit Membrane

A term referring to the cell membrane because it shares the same general biochemical and structural arrangement across all biological organisms.

Trilaminar Structure

The characteristic $8-10\,nm$ thick electron microscope appearance of the cell membrane, consisting of an outer and an inner electron-dense lamina separated by a central electron-lucent layer.

Integral Proteins

Membrane proteins that are directly inserted into the phospholipid bilayer.

Peripheral Proteins

Membrane proteins that are attached to the inner or outer surfaces of the lipid bilayer rather than inserted into its hydrophobic core.

Transmembrane Proteins

Proteins that span the entire thickness of the lipid bilayer.

Zonula Occludens

Belt-like occluding junctional complexes in epithelial cells involving transmembrane occludin and claudin, which are linked to spectrin via peripheral proteins $ZO-1$ and $ZO-2$.

Zonula Adherens

Anchoring junctional complexes found in tall columnar epithelial cells that utilize transmembrane cadherin and connect internally to a circumferential band of actin microfilaments.

Desmosomes (Macula Adherens)

Disk-shaped anchoring junctions prominent in the epidermis that provide mechanical strength by linking transmembrane cadherins to dense cytoplasmic plaques attached to intermediate filaments of keratin or desmin.

Hemidesmosomes

Asymmetric anchoring junctions structurally resembling half of a desmosome, containing the matrix receptor integrin to anchor cells to the basement membrane in the dermis.

Gap Junctions (Nexus)

Communicating junctions separated by a $2-4\,nm$ intercellular gap that permit the direct passage of electrical signals, ions, and small water molecules between cells.

Connexons

Protein complexes that assemble across neighboring cell membranes to form channels within gap junctions.

Endocrine Communication

A mode of cellular communication mediated by hormones secreted into the bloodstream.

Neurocrine Communication

A distant signaling pathway mediated by the release and action of neurotransmitters.

Paracrine Communication

Local cellular signaling in which chemical messengers are transmitted to neighboring cells located within diffusion distance.

Autocrine Signaling

A regulatory mechanism in which a cell produces signals that bind to receptors on its own surface, a phenomenon notably characterized in cancer cells.

Microvilli

Fingerlike, nonmotile cell surface projections supported by an internal core of microfilaments.

Stereocilia

Long, nonmotile variants of microvilli that feature an internal core of microfilaments.

Cilia

Long, motile surface projections containing a microtubule core that produce the unidirectional transport of extracellular materials.

Flagella

Cell surface modifications with a microtubule core that function to propel and move the cell in any direction.

Endocytosis

The cellular transport process that internalizes molecules into the cell across the plasma membrane.

Exocytosis

The active process by which membrane-bound secretory vesicles release their contents outside the cell across the plasma membrane.

Transcytosis

The vesicular transport process responsible for moving molecules across or within the interior of a cell.

Cytosol

The aqueous intracellular solution containing water, ions, metabolites, enzymes, cytoskeletal subunits, and RNAs in which organelles are suspended.

Nuclear Pore

A multiprotein complex spanning both layers of the nuclear membrane, composed of approximately $30$ different proteins, that regulates the selective transit of macromolecules.

Nucleolus

A dense, ovoid, non-membrane-bound subnuclear compartment responsible for rRNA transcription and ribosomal subunit assembly.

Pars Granulosa

The subregion of the nucleolus that serves as the primary site of preribosomal particle assembly.

Pars Fibrosa

The nucleolar compartment containing ribonucleoprotein filaments, rRNA genes, and transcription factors.

Euchromatin

The dispersed, uncoiled form of chromatin that is transcriptionally active and prominent in cells actively synthesizing proteins.

Heterochromatin

The densely condensed form of chromatin that is transcriptionally inactive.

Cristae

Infoldings of the mitochondrial inner membrane that project into the matrix and are studded with particles involved in ATP synthesis.

Mitochondrial Dense Bodies

Electron-dense structures located within the mitochondrial matrix that are rich in calcium ($Ca^{++}$), functioning as an intracellular calcium reservoir.

Peroxisomes (Microbodies)

Small, single-membrane-delimited oxidative organelles containing over $40$ enzymes, including urate oxidase and catalase, found abundantly in hepatocytes and kidney proximal tubule cells.

Rough Endoplasmic Reticulum (rER)

An interconnected network of flattened cisternae studded with ribosomes that is continuous with the outer nuclear membrane and primarily dedicated to protein synthesis.

Ergastoplasm

The term given to aggregates of intensely basophilic, well-developed rough endoplasmic reticulum found in pancreatic acinar cells.

Nissl Substance

The term used for prominent basophilic accumulations of rough endoplasmic reticulum in neurons.

Smooth Endoplasmic Reticulum (sER)

A ribosome-free network of tubular sacs involved in lipid and steroid synthesis, detoxification of noxious compounds, and intracellular calcium sequestration.

Sarcoplasmic Reticulum

A specialized form of smooth endoplasmic reticulum found in muscle cells that sequesters and releases $Ca^{++}$ to trigger muscle contraction.

Ribosome

A non-membranous particle ($15-20\,nm$ in diameter) composed of rRNA and proteins, divided into an embryo-shaped small subunit and a boat-shaped large subunit, that carries out protein translation.

Golgi Complex

An organelle consisting of $3-10$ stacked, bow-shaped cisternae with a convex cis-face and concave trans-face, responsible for post-translational modification, sorting, and packaging of proteins.

Lysosomes

Membrane-delimited organelles containing acid-dependent hydrolytic enzymes that digest macromolecules, clear worn-out cellular parts, and participate in apoptosis; discovered by Christian René de Duve.

Microfilaments

Cytoskeletal fibers measuring $3-6\,nm$ in diameter composed predominantly of the contractile protein actin, which interact with myosin to generate cellular movement and contraction.

Microtubules

Cylindrical cytoskeletal tubes measuring $20-25\,nm$ in diameter composed of alpha- and beta-tubulin dimers that form mitotic spindles, cilia, flagella, and organelle tracks.

Intermediate Filaments

Tough cytoskeletal fibers approximately $10\,nm$ in diameter that reinforce cell structure, provide tensile strength, and integrate with anchoring junctions like desmosomes.

Centrioles

Two barrel-shaped organelles composed of microtubules located within the centrosome that migrate to opposite poles to organize the mitotic spindle during cell division.