Quiz 3 - Cell Signaling and Cancer (BIOL 215)

Tissue

An ensemble of similar cells from the same origin that together carry out a specific physiological function.

Epithelial Tissue

A sheet of tightly bound cells covering body surfaces and lining internal organs, exhibiting distinct structural and functional polarity.

Connective Tissue

Tissue that directly bears mechanical stresses of tension and compression, characterized by cells dispersed within an extracellular matrix.

Apical Surface

The upper, exposed surface of an epithelial cell that faces the lumen or external environment.

Basal Surface

The bottom surface of an epithelial cell anchored to the underlying basal lamina.

Basolateral Domain

The combined lateral (side) and basal (bottom) plasma membrane regions of an epithelial cell, separated from the apical domain by tight junctions.

Basal Lamina (Basal Membrane)

A thin, specialized mat of extracellular matrix underlying epithelial sheets, anchoring them to connective tissue.

Extracellular Matrix (ECM)

The complex network of proteins and carbohydrates secreted outside cells that provides structural support and bears mechanical loads.

Collagen

A major fibrous protein in the ECM that provides high tensile strength to tissues.

Procollagen

The precursor form of collagen synthesized inside cells before being secreted and assembled into extracellular collagen fibers.

Fibronectin

An ECM glycoprotein that attaches cells to collagen fibers within the matrix.

Elastin

A protein in connective tissue that provides elasticity, allowing tissues to stretch and recoil.

Glycosaminoglycan (GAG)

Unbranched polysaccharide chains composed of repeating disaccharide units that form hydrated gels in the ECM.

Proteoglycan

An ECM molecule composed of a core protein covalently bound to one or more glycosaminoglycan (GAG) chains.

Glycoprotein

A protein covalently conjugated to short, branched oligosaccharides.

Glycocalyx

The carbohydrate-rich coat on the outer surface of eukaryotic cell membranes formed by glycoproteins and glycolipids.

Tight Junction

An impermeable barrier formed by occludin and claudin proteins that seals adjacent epithelial cells together, preventing fluid leakage between cells and preserving membrane protein polarity.

Adherens Junction

A cell-cell junction where transmembrane cadherin proteins link adjacent cell membranes to internal actin filaments.

Desmosome

A cell-cell junction where cadherin proteins connect adjacent cell membranes to internal keratin intermediate filaments, providing mechanical toughness.

Hemidesmosome

A cell-matrix junction where integrin proteins anchor internal keratin intermediate filaments to the underlying basal lamina.

Gap Junction

A cell-cell junction composed of connexon channels (made of connexins) that allow small inorganic ions and water-soluble molecules to pass directly between neighboring cells.

Plasmodesmata

Microscopic membrane-lined channels passing through plant cell walls that enable direct intercellular transport and communication.

Autocrine Signaling

A form of chemical signaling where a cell secretes a signal molecule that binds to its own surface receptors.

Paracrine Signaling

Local signaling where a cell releases signal molecules that diffuse through extracellular fluid to target nearby cells.

Endocrine Signaling

Long-distance signaling where endocrine cells release hormones into the bloodstream to reach distant target cells.

Juxtacrine (Contact-Dependent) Signaling

Short-range signaling that requires direct contact between a membrane-bound signal molecule on one cell and a receptor on an adjacent cell.

Neuronal Signaling

A specialized form of paracrine signaling where electrical impulses travel along an axon to trigger neurotransmitter release across a synapse to target dendrites.

Ligand

A chemical signaling molecule that specifically binds to a target receptor to initiate a cellular response.

Receptor

A protein on the cell surface or inside the cell that specifically binds a ligand and undergoes a conformational change to transduce the signal.

Signal Transduction

The multi-step process by which an extracellular signal is converted into a specific intracellular response through a signaling cascade.

Signal Amplification

The multiplication of a signal during a cascade, where a single activated upstream molecule activates many downstream target molecules.

Kinase

An enzyme that transfers a phosphate group from ATP to specific target amino acid residues (serine, threonine, or tyrosine) on proteins.

Phosphatase

An enzyme that removes phosphate groups from proteins, deactivating kinase-mediated signaling.

GTPase-Activating Protein (GAP)

A regulatory protein that stimulates a GTPase to hydrolyze bound GTP to GDP, turning the GTPase OFF.

Guanine Exchange Factor (GEF)

A regulatory protein that causes a GTPase to release bound GDP so GTP can bind, turning the GTPase ON.

Monomeric GTPase (e.g., Ras)

A single-subunit molecular switch protein (like Ras) that cycles between active GTP-bound and inactive GDP-bound states to relay signals downstream.

Trimeric G-Protein

A three-subunit (,,) protein complex associated with G-protein-coupled receptors (GPCRs) that is activated when the subunit exchanges GDP for GTP.

Receptor Tyrosine Kinase (RTK)

An enzyme-coupled cell-surface receptor that dimerizes and cross-phosphorylates tyrosine residues on its intracellular domain upon ligand binding.

G-Protein-Coupled Receptor (GPCR)

A 7-transmembrane cell-surface receptor that undergoes a conformational change upon ligand binding to activate an associated trimeric G-protein.

Second Messenger

Small, non-protein intracellular molecules or ions (e.g., cAMP, IP3, DAG, Ca2+) that rapidly diffuse and propagate signaling cascades inside the cell.

Adenylyl Cyclase

An enzyme activated by G-proteins that converts ATP into the second messenger cyclic AMP (cAMP).

Phospholipase C (PLC)

An enzyme activated by GPCRs that cleaves PIP2 in the plasma membrane into the second messengers IP3 and DAG.

Interphase

The extended phase of the cell cycle comprising G1, S, and G2 phases during which the cell grows and replicates its DNA prior to nuclear division.

G0 Phase

A non-dividing state entered by cells exiting the cell cycle.

Quiescent

A "quiet" state in G0 where cells are not actively dividing but retain the capacity to re-enter the cell cycle if triggered by external signals.

Senescent

A permanent non-dividing cell state typically induced by cell aging or unrepairable DNA damage.

Cyclin

A family of regulatory proteins whose concentrations oscillate throughout the cell cycle to bind and activate specific cyclin-dependent kinases (Cdks).

Cyclin-Dependent Kinase (Cdk)

A protein kinase that, when bound to a specific cyclin, phosphorylates key downstream target proteins to drive the cell into the next cell cycle stage.

Mitogen

An extracellular signaling molecule that stimulates cell division by triggering pathways that activate G1-Cdk and G1/S-Cdk complexes.

Retinoblastoma (Rb) Protein

An inhibitory protein that blocks transcription required for entry into S-phase; phosphorylation by G1/S-Cdk inactivates Rb and releases transcription factors.

p53

A tumor suppressor protein activated by DNA damage that induces transcription of p21, a Cdk inhibitor that halts the cell cycle.

Cdc25 Phosphatase

An activating phosphatase that removes inhibitory phosphate groups from M-Cdk (MPF) to trigger entry into mitosis.

Wee1 Kinase

An inhibitory kinase that adds inhibitory phosphate groups to M-Cdk to keep it inactive until DNA replication is complete.

Ubiquitylation

The covalent attachment of ubiquitin molecules to target proteins (such as cyclins by APC/C), targeting them for destruction by the proteasome.

Apoptosis

Programmed, orderly cell death triggered by developmental signals or severe cell damage.