e3 - Signal Transduction IIB and IIC

Endocrine vs. paracrine signaling

Endocrine: long-distance via blood. Paracrine: short-distance.

Autocrine vs. juxtacrine signaling

Autocrine: acts on the same cell. Juxtacrine: requires cell contact.

Signal transduction

A cell's response to ligand-receptor binding.

Agonist vs. antagonist

Agonist activates a receptor; antagonist blocks activation.

Signal amplification

One signaling step activates many molecules in the next step.

GPCR

A receptor with seven transmembrane helices that activates a G protein.

G protein activation

Ligand binds GPCR; Gα swaps GDP for GTP and separates from Gβγ.

G protein inactivation

Gα hydrolyzes GTP to GDP and reassociates with Gβγ.

Adenylyl cyclase

Converts ATP into the second messenger cAMP.

cAMP target

Activates protein kinase A (PKA), which phosphorylates target proteins.

IP₃ and DAG production

Phospholipase C cleaves PIP₂ into IP₃ and DAG.

IP₃ function

Binds ER receptors, releasing Ca²⁺ into the cytosol.

Ca²⁺ and DAG

Activate protein kinase C (PKC), which phosphorylates target proteins.

Calcium-induced calcium release

Ca²⁺ opens ryanodine receptors, causing more ER Ca²⁺ release.

Calmodulin

Binds Ca²⁺ and helps activate cellular processes.

Receptor tyrosine kinases (RTKs)

Receptors whose kinase activity is stimulated by ligand binding.

RTK activation

Ligand causes receptors to pair or cluster and autophosphorylate.

Autophosphorylation

A receptor phosphorylates itself or another receptor of the same type.

Ras

Small G protein that promotes cell proliferation when GTP-bound.

Ras–MAP kinase pathway

Ras → Raf → MEK → MAP kinase.

MAP kinase function

Phosphorylates transcription factors that alter gene expression.

Ras inactivation

GAP promotes GTP hydrolysis, leaving Ras bound to GDP.

Phosphorylation cascade

A sequence of proteins activating or modifying one another by phosphorylation.

Signaling crosstalk

Different signaling pathways influence or share components.

Steroid hormone signaling

Steroid hormones cross the membrane, bind intracellular receptors, and regulate gene transcription.