בchapter eight Cell Communication and Signal Transduction

Sixty vocabulary flashcards covering key terms and definitions from the lecture on cell communication and signal transduction.

Second Messenger

A small intracellular molecule that relays and amplifies signals received by cell-surface receptors.

cAMP (Cyclic AMP)

A common second messenger derived from ATP that activates Protein Kinase A.

Advantages of Second Messengers – Signal Amplification

One receptor–ligand event can generate many second-messenger molecules, greatly multiplying the cellular response.

Advantages of Second Messengers – Speed

Second messengers diffuse rapidly, allowing cells to respond almost instantly to extracellular cues.

Crosstalk

Interaction among multiple signaling pathways inside a cell, enabling coordination of responses.

Extracellular Signal

Any molecule released outside a cell that can trigger a response in target cells.

Intracellular Receptor

A receptor located inside the cell, often in the nucleus, that binds lipid-soluble signals.

Estrogen

A steroid hormone that diffuses through membranes and binds intracellular receptors to regulate gene transcription.

Steroid Hormone

Hydrophobic, lipid-based hormone capable of crossing the plasma membrane without a transporter.

Hydrophobic Signaling Molecule

A non-polar messenger that readily dissolves in the lipid bilayer to reach intracellular receptors.

Gene Transcription Activation

Process initiated when certain receptors or transcription factors stimulate RNA synthesis from DNA.

Apoptosis

Programmed cell death in which a cell self-destructs in an orderly manner.

Programmed Cell Death

Synonym for apoptosis; essential for removing unnecessary or damaged cells.

Signal Transduction Pathway

Series of molecular events converting an extracellular signal into a specific cellular response.

Glucose Transporter Induction

Increase in membrane glucose carriers when yeast cells detect external glucose.

Phototropism

Growth of a plant toward light, controlled by unequal distribution of auxin.

Auxin

Plant hormone that mediates phototropic bending by promoting cell elongation on the shaded side.

Direct Intercellular Signaling

Communication through cell junctions that allow molecules to pass directly from one cell to another.

Gap Junction

Animal cell channel that permits direct passage of ions and small molecules between neighboring cells.

Plasmodesmata

Cytoplasmic channels through plant cell walls enabling direct signaling between cells.

Contact-Dependent Signaling

Signaling in which membrane-bound molecules on one cell interact with receptors on an adjacent cell.

Autocrine Signaling

A cell releases a signal that binds receptors on its own surface or nearby identical cells.

Paracrine Signaling

Signal molecules diffuse locally and influence neighboring cells but not the secreting cell itself.

Endocrine Signaling

Long-distance communication in which hormones travel through the bloodstream to distant targets.

Hormone

A signaling molecule produced in one tissue and carried through circulation to affect other tissues.

Receptor Activation

Initial stage of signaling when a ligand binds and changes a receptor’s conformation.

Ligand

A specific molecule that binds non-covalently and reversibly to a receptor.

Cell Surface Receptor

Membrane-embedded protein that binds hydrophilic ligands unable to cross the lipid bilayer.

Enzyme-Linked Receptor

Transmembrane protein that functions as an enzyme, often a kinase, upon ligand binding.

Kinase

Enzyme that transfers a phosphate group from ATP to a substrate protein.

Protein Kinase Receptor

Enzyme-linked receptor whose intracellular domain phosphorylates specific amino acids on proteins.

G-Protein–Coupled Receptor (GPCR)

A seven-pass membrane receptor that activates a heterotrimeric G protein when occupied by a ligand.

G Protein

Trimeric protein (α, β, γ) that cycles between GDP-bound inactive and GTP-bound active states.

GDP

Guanosine diphosphate; bound to inactive G-protein α-subunit.

GTP

Guanosine triphosphate; binds active G-protein α-subunit, triggering downstream signaling.

Alpha Subunit

The G-protein component that dissociates upon GTP binding to regulate effector enzymes.

Beta-Gamma Dimer

The β and γ subunits of a G protein that can modulate certain signaling pathways when separated from α.

Ligand-Gated Ion Channel

Membrane protein that opens or closes an ion pore in response to ligand binding.

Signal Transduction Cascade

Sequential activation of multiple proteins, often kinases, transmitting a signal inward.

Relay Protein

Intracellular protein that passes a signal from an activated receptor to downstream targets.

RAS

Small GTPase relay protein linking growth-factor receptors to kinase cascades.

Protein Kinase

General term for any enzyme that phosphorylates proteins to modulate their function.

Phosphorylation

Addition of a phosphate group to a protein, frequently altering its activity or location.

Transcription Factor

Protein that binds DNA and regulates transcription; often activated by phosphorylation.

Amplification in Signaling

Phenomenon whereby one activated molecule activates many downstream molecules, increasing response strength.

Growth Factor

Extracellular protein, such as EGF, that promotes cell growth and division.

Epidermal Growth Factor (EGF)

Specific growth factor stimulating epithelial cell division via receptor tyrosine kinase activation.

Cell Division Stimulation

Process by which growth factors and signaling pathways push cells into the cell cycle.

First Messenger

The extracellular ligand that initially binds a receptor (e.g., epinephrine).

Protein Kinase A (PKA)

cAMP-dependent kinase that phosphorylates numerous proteins to mediate cellular responses.

Glycogen Breakdown

PKA-mediated phosphorylation of enzymes that liberates glucose units for ATP production.

Glycogen Synthesis Inhibition

PKA-driven phosphorylation that suppresses enzymes building glycogen, conserving glucose for energy.

Phosphodiesterase

Enzyme that converts cAMP to AMP, thereby terminating cAMP signaling.

AMP (Adenosine Monophosphate)

Product of cAMP hydrolysis; cannot activate PKA.

Protein Phosphatase

Enzyme that removes phosphate groups from proteins, reversing kinase actions.

Signal Termination

Processes such as ligand dissociation, cAMP breakdown, and dephosphorylation that stop a signaling pathway.

Amplification via Kinase Cascade

Each activated kinase activates multiple downstream kinases, ensuring a robust response.

Signal Speed

Rate at which a cell responds, enhanced by diffusible second messengers like cAMP.

Receptor Conformational Change

Structural alteration in a receptor upon ligand binding that triggers intracellular signaling.

Signal Specificity

Selective binding between a ligand and its receptor ensuring appropriate cellular responses.

Cell Response

Final outcome of signaling, such as enzyme activation, gene expression, or apoptosis.