Cell Bio Test #4

Autocrine signaling

A cell releases a signaling molecule that binds to receptors on its own surface, allowing it to regulate its own activity

Contact-dependent signaling

Signaling occurs through direct cell‑to‑cell contact, often via membrane‑bound ligands that engage receptors on the neighboring cell

Endocrine signaling

Hormones are secreted into the bloodstream and travel long distances to act on target cells throughout the body

Feedback regulation

Biological pathways adjust their activity through loops (positive or negative) that sense the output and modify upstream steps to maintain homeostasis

GAP(GTPase Activating Protein)

a regulatory protein that speeds up the intrinsic GTP‑hydrolysis activity of a G‑protein, converting the active GTP‑bound form back to the inactive GDP‑bound state

GEF(Guanine Exchange Factor)

a protein that promotes the release of GDP from a G‑protein and its replacement with GTP, thus activating the G‑protein

G-Protein

a heterotrimeric or monomeric GTP‑binding protein that cycles between an inactive GDP‑bound state and an active GTP‑bound state to transmit signals from receptors to downstream effectors

Monomeric GTPase

a single‑subunit small G‑protein (e.g., RAS, RHO, RAC) that directly binds and hydrolyzes GTP

Paracrine signaling

a mode of cell‑to‑cell communication in which a secreted factor diffuses locally to affect neighboring cells within the same tissue, without entering the bloodstream

Protein kinases

enzymes that transfer a phosphate group from ATP to specific amino‑acid residues (usually Ser, Thr, or Tyr) on target proteins, typically activating or modulating their function

Protein phosphatase

an enzyme that removes phosphate groups from phosphorylated proteins, reversing the action of kinases and often returning proteins to an inactive state

AMP

nucleotide that can be phosphorylated to ADP or ATP and also serves as a signaling molecule in certain pathways

AMP phosphodiesterase

enzyme (commonly called phosphodiesterase) that hydrolyzes cyclic AMP (cAMP) to AMP, terminating the second‑messenger signal

Adenylyl cyclase

membrane‑bound enzyme that converts ATP into the second messenger cAMP, typically activated by Gₛ‑type G proteins

G-alpha subunit

catalytic component of heterotrimeric G proteins; it binds GDP/GTP and, when GTP‑bound, interacts with downstream effectors such as adenylate cyclase

G-beta subunit

Forms a stable dimer with G γ; together they can directly modulate ion channels (e.g., GIRK) and other signaling proteins

GPCR

G‑protein‑coupled receptor, a seven‑transmembrane protein that detects extracellular ligands and activates intracellular G proteins

cAMP

second messenger synthesized by adenylyl cyclase that activates protein kinase A and other effectors

Calmodulin

calcium‑binding protein that undergoes conformational changes upon Ca²⁺ binding and then regulates various enzymes and channels

Cholera toxin

bacterial exotoxin that ADP‑ribosylates the Gₛ α subunit, locking it in the active GTP‑bound state and causing persistent cAMP production

DAG

Diacylglycerol, a lipid second messenger generated by phospholipase C that activates protein kinase C and helps recruit other signaling proteins

G-gamma subunit

Membrane-anchored partner of Gβ contributing to effector activation after receptor stimulation

IP3

second messenger generated when phospholipase C cleaves PIP₂; it binds receptors on the endoplasmic reticulum to trigger calcium release into the cytosol

Nitric oxide synthase

Enzyme catalyzing conversion of arginine into nitric oxide

NO

Short-lived gas activating guanylyl cyclase to raise cGMP and relax smooth muscle

Pertusiss toxin

Bacterial toxin preventing activation of Gαi by blocking GDP–GTP exchange

Phospholipase C

effector enzyme activated by Gq proteins that hydrolyzes PIP₂ into IP₃ and DAG, initiating calcium release and PKC activation

Notch

Transmembrane receptor releasing intracellular domain after ligand binding to directly regulate transcription