Cell Signaling and Tissue Architecture

Vocabulary practice flashcards covering cell signaling pathways, receptor types, tissue organization, cytoskeletal elements, cell junctions, and extracellular matrix functions.

Signaling cell

The source cell that produces and releases a signaling molecule to communicate with other cells.

Signaling molecule (Ligand)

A chemical messenger, such as a peptide, lipid, or gas, released by a signaling cell that binds specifically to a receptor protein on or inside a responding cell.

Receptor protein

A protein located on or inside a responding cell that binds a specific signaling molecule, causing a conformational change that activates the receptor.

Responding cell

The recipient cell possessing specific receptor proteins that detect a signaling molecule and elicit a physiological response.

Endocrine signaling

A mode of long-distance communication in which signaling molecules, such as hormones like adrenaline, estrogen, or testosterone, travel through the circulatory system to reach distant target cells.

Paracrine signaling

A form of short-distance cell communication where small, water-soluble signaling molecules, such as growth factors, diffuse across a few cell diameters to neighboring cells.

Autocrine signaling

A signaling mechanism where the releasing cell and the responding cell are the same cell; important in embryonic development.

Contact-dependent signaling

A signaling mechanism requiring direct physical contact, where a transmembrane protein on one cell acts as the signal and binds to a receptor protein on an adjacent cell.

Delta-Notch signaling

A contact-dependent signaling pathway in central nervous system development in which undifferentiated cells expressing Delta become neurons, while adjacent cells expressing Notch differentiate into glial cells.

Cell-surface receptor

A transmembrane protein embedded in the plasma membrane that binds polar signaling molecules that cannot cross the hydrophobic core of the cell membrane.

Intracellular receptor

A receptor located in the cytoplasm or nucleus that binds small, nonpolar signaling molecules (such as steroid hormones) that diffuse across the plasma membrane.

G protein-coupled receptor (GPCR)

A large, evolutionarily conserved family of cell-surface receptors that associates with an intracellular G protein upon ligand binding, typically triggering rapid, short-term responses.

Heterotrimeric G protein

A membrane-associated molecular switch composed of $\alpha$, $\beta$, and $\gamma$ subunits that is inactive when bound to GDP and active when the $\alpha$-subunit exchanges GDP for GTP and dissociates.

Adenylyl cyclase

A membrane enzyme activated by the GTP-bound $\alpha$-subunit of a G protein that converts ATP into the second messenger cyclic AMP (cAMP).

Cyclic AMP (cAMP)

A diffusible second messenger synthesized from ATP by adenylyl cyclase that binds to and activates protein kinase A (PKA).

Protein kinase A (PKA)

An intracellular enzyme activated by cAMP that phosphorylates specific target proteins, such as proteins in heart muscle cells to accelerate heart rate.

Signal amplification

A mechanism in signal transduction cascades where a single ligand-bound receptor activates multiple G proteins, enzymes generate large amounts of second messengers, and kinases activate multiple downstream targets.

Phosphatase

An enzyme that terminates signaling pathways by removing phosphate groups from activated proteins, converting them back to an inactive state.

Receptor kinase

A widespread cell-surface receptor that functions as an enzyme, autophosphorylating cytoplasmic residues to transmit signals that often govern long-term responses like changes in gene expression.

Dimerization

The pairing of two receptor kinase subunits upon ligand binding, which triggers cross-phosphorylation of their cytoplasmic domains.

Platelet-derived growth factor (PDGF)

A signaling molecule released from damaged cells during tissue injury that binds receptor kinases to initiate cellular repair and division.

Ras

A single-subunit cytoplasmic G protein activated downstream of receptor kinases in the MAP kinase pathway; mutations that lock Ras in a permanently GTP-bound state cause approximately $30\%$ of all human cancers.

MAP kinase pathway

A sequential phosphorylation cascade triggered by active GTP-bound Ras where a series of kinases activate one another, ultimately entering the nucleus to turn on gene expression for cell division.

Ligand-gated ion channel

A cell-surface receptor that alters membrane permeability by opening an ion-conducting pore when bound to a specific ligand, such as channels that admit calcium ions during muscle contraction.

Tissue

A community of cells working together to perform a specific function.

Organ

A structure composed of two or more tissues organized together to perform an integrated, specific physiological function.

Epithelial tissue

A fundamental animal tissue type arranged in one or more layers of cells that lines body cavities and covers external surfaces, characterized by a high turnover rate.

Connective tissue

A supportive animal tissue type containing relatively few cells suspended in an extensive, thick extracellular matrix, including blood, bone, cartilage, and adipose tissue.

Epidermis

The outer water-resistant and protective barrier of the skin consisting of stratified epithelial cells.

Keratinocyte

The primary epithelial cell type of the epidermis that provides physical protection to underlying body tissues.

Melanocyte

A specialized cell found in the epidermis that synthesizes melanin pigments to produce skin coloration.

Dermis

The strong, flexible connective tissue layer beneath the epidermis that supports it physically, provides nutrients, and contains blood vessels, nerve endings, and fibroblasts.

Fibroblast

The predominant cell type in the dermis and animal connective tissue that synthesizes and secretes the extracellular matrix.

Extracellular matrix (ECM)

An insoluble meshwork composed of proteins and polysaccharides that is synthesized and modified by cells to provide structural support and informational cues.

Basal lamina

A specialized sheet-like layer of extracellular matrix situated beneath all epithelial tissues that provides structural scaffolding and flexible support.

Middle lamella

The outermost layer of the plant extracellular matrix/cell wall that functions primarily in adhering adjacent plant cells together.

Secondary cell wall

An internal layer of the plant cell wall composed mostly of cellulose and lignin that hardens and reinforces the cell wall structure.

Lignin

A rigid polymer found within the secondary cell wall of plants that hardens and strengthens plant tissues.

Collagen

The most abundant protein in the extracellular matrix and the most abundant animal protein on Earth, organized into intertwined triple-helix fibers resembling steel cables for immense tensile strength.

Cytoskeleton

An internal framework of protein filaments within eukaryotic cells that provides structural support, maintains cell shape, and facilitates movement of materials.

Microfilaments

The thinnest cytoskeletal elements, composed of actin monomers arranged into a double helix, located just under the cell membrane to maintain shape, drive crawling, and execute cytokinesis.

Intermediate filaments

Durable, cable-like cytoskeletal fibers intermediate in diameter between microfilaments and microtubules that provide mechanical strength to the cell and nucleus.

Epidermolysis bullosa

A disease caused by mutations in keratin intermediate filament genes, leading to defective mechanical support and fragile skin that blisters easily.

Microtubules

The largest cytoskeletal elements, constructed as hollow tubes of $\alpha$- and $\beta$-tubulin heterodimers that radiate from the centrosome to organize organelles and separate chromosomes.

Dynamic instability

A property of microtubules characterized by rapid cycles of depolymerization (shortening) followed by slower polymerization (growth), facilitating chromosome capture during cell division.

Centrosome

The central microtubule-organizing center of animal cells from which microtubules radiate, orienting with their minus ends inward and plus ends outward.

Kinesin

An ATP-dependent motor protein that carries cargo, such as vesicles, along microtubules toward the plus end.

Dynein

An ATP-dependent motor protein that moves cargo along microtubules toward the minus end.

Cadherins

Transmembrane cell adhesion molecules that mediate cell-to-cell adhesion by binding homophilically to cadherins of the identical type on an adjacent cell.

Integrins

Transmembrane cell adhesion proteins whose extracellular domains bind components of the extracellular matrix and whose intracellular domains link to cytoskeletal filaments.

Adherens junction

An anchoring cell junction that uses cadherins to bind adjacent cells together while linking intracellularly to actin microfilaments.

Desmosome

A point-like anchoring junction that connects adjacent cells via cadherins and anchors to intermediate filaments in the cytoplasm, granting high mechanical resistance.

Hemidesmosome

An anchoring junction that utilizes integrins to anchor the intermediate filaments of an epithelial cell to the underlying basal lamina.

Tight junction

A barrier junction formed by claudins and occludins that seals the space between neighboring epithelial cells, preventing fluids and molecules from leaking between them.

Gap junction

A communicating junction in animal cells formed by rings of connexin proteins that align to create direct channels for passage of ions and signaling molecules between adjacent cells.

Plasmodesmata

Intercellular communication channels traversing plant cell walls where the plasma membrane and cytoplasm of adjacent plant cells are continuous.

Metastasis

The migration of malignant cells from a primary tumor through the bloodstream to colonize distant tissues, requiring cancer cells to cross the capillary basal lamina twice using specific integrins.

Laminins

Extracellular matrix proteins that direct cell differentiation and morphology, providing signals necessary for cultured neurons to extend axon-like projections.