Cell Signaling and Signal Transduction Flashcards

A comprehensive set of vocabulary terms covering cell signaling mechanisms, receptor types, second messengers, and intracellular cascades based on Chapter 16 lecture notes.

Signal Transduction

The process of converting one type of signal to another within a cell.

Receptor proteins (receptors)

Proteins that detect signal molecules to initiate a response in a target cell.

Autocrine signaling

A style of local cell communication where the signaling cell is also the target cell.

Agonist

A molecule that activates a signaling pathway by mimicking the original signal.

Antagonist

A molecule that blocks a signaling pathway by inhibiting the signal.

Steroid hormones

Small, hydrophobic signaling molecules derived from cholesterol, such as cortisol, estradiol, and testosterone, that can cross the plasma membrane.

Nitric oxide ($NO$)

A dissolved gas that acts as a local mediator and can enter cells by diffusion to directly activate intracellular enzymes like guanylyl cyclase.

Guanylyl cyclase

An enzyme activated by $NO$ that converts $GTP$ into cyclic $GMP$ ($cGMP$).

Nuclear receptor protein

An intracellular receptor in the cytosol or nucleus that acts as a transcription regulator when bound to a signal molecule like cortisol.

Ion-channel-coupled receptors

Cell-surface receptors that convert a chemical signal into an electrical signal by opening or closing in response to a neurotransmitter.

G-protein-coupled receptors (GPCRs)

A large family of cell-surface receptors characterized by 7 transmembrane domains that interact with trimeric G-proteins.

Enzyme-coupled receptors

Cell-surface receptors that either act as enzymes themselves or associate with enzymes inside the cell, such as Receptor Tyrosine Kinases (RTKs).

Protein kinase

An enzyme that covalently attaches a phosphate group from $ATP$ to a protein, acting as a molecular switch.

Protein phosphatase

An enzyme that removes a phosphate group from a protein, reversing the action of a protein kinase.

GTP-binding proteins

Molecular switches that toggle between an active state bound to $GTP$ and an inactive state bound to $GDP$.

Trimeric G-protein

A protein complex consisting of $\alpha$, $\beta$, and $\gamma$ subunits where the $\alpha$ subunit binds $GDP$ or $GTP$.

Adenylyl cyclase

A membrane-bound enzyme activated by G-proteins that produces the second messenger cyclic $AMP$ ($cAMP$).

Second messenger

Small intracellular signaling molecules, such as $cAMP$, $IP_3$, and $Ca^{2+}$, that relay and amplify signals.

cAMP phosphodiesterase

An enzyme that terminates signaling by converting cyclic $AMP$ to $AMP$.

PKA (Cyclic-AMP-dependent protein kinase)

The primary target of cyclic $AMP$ that phosphorylates various enzymes to elicit cellular responses.

Phospholipase C

A membrane-bound enzyme that cleaves inositol phospholipids to generate the second messengers $IP_3$ and $DAG$.

Inositol trisphosphate ($IP_3$)

A second messenger that targets the endoplasmic reticulum to trigger the release of $Ca^{2+}$ ions.

Diacylglycerol ($DAG$)

A small messenger molecule produced by phospholipase C that remains in the plasma membrane to help activate Protein Kinase C ($PKC$).

Calmodulin

A widespread $Ca^{2+}$-binding protein that undergoes a conformational change to activate target proteins like $CaM$-kinase.

Receptor Tyrosine Kinases (RTKs)

Enzyme-coupled receptors that, upon signal binding, form dimers and phosphorylate their own cytoplasmic tyrosines.

Ras protein

A small, monomeric $G$-protein tethered to the plasma membrane that is activated by many $RTKs$ via a $Ras$-$GEF$ (GTP exchange factor).

MAP-kinase cascade

A signaling pathway activated by Ras involving a series of mitogen-activated protein kinases leading to changes in protein activity or gene expression.

PI 3-kinase

An enzyme that phosphorylates inositol phospholipids in the plasma membrane, creating docking sites for signaling proteins like $Akt$.

Akt (Protein Kinase B)

A signaling protein that promotes cell survival by inactivating the pro-apoptotic protein Bad and promotes cell growth by activating Tor.

Tor (Target Of Rapamycin)

A serine/threonine kinase that stimulates cell growth and is inhibited by the anticancer drug rapamycin.

Bad

A protein that promotes apoptosis (cell suicide) when unphosphorylated but is inactivated by phosphorylation by $Akt$.