cell signals

A transducer is any device that converts variations in one physical quantity into variations in another, such as from an external signal into an intracellular response.

• A receptor is activated by a signal. • The activated receptor triggers a cascade of reactions inside the cell. • The cascade leads to an end reaction and a physiological response.

• Presence and abundance of the signal. • Presence and abundance of the receptor.

• Perception of the signal. • Triggering a reaction that initiates a signaling cascade.

• G-protein coupled receptors (GPCR) • Receptor-like kinases (RLK) • Ion channel receptors (ICRs) • Cytoplasmic receptors (CRs) • Sensor molecules (e.g., phytochrome for light perception)

• Located in the plasma membrane. • Composed of: N-terminal receptor domain Seven trans-membrane domains C-terminal intracellular extensions.

• Composed of: Extracellular N-terminal receptor domain. Transmembrane region. C-terminal protein kinase in the cytosol. • Binding of ligand activates the kinase.

• Ion channels associated with receptors open and close in response to: Physical signals: light, sound, stretching, charge difference. Chemical signals: hormones, metabolites. • Movement of ions triggers a signaling cascade.

• These receptors bind to small ligands capable of diffusing across the plasma membrane. • Ligand binding causes a conformational change, leading to the release of the receptor from a chaperone protein and its movement into the nucleus or other compartments.

• Small molecules that relay and amplify the signal within the cell. • Examples include cyclic nucleotides, calcium ions, nitric oxide (NO), and reactive oxygen species (ROS).

• Calcium is a major secondary signaling component. • Calcium ions move into the cytosol, triggering signaling cascades and activating calcium-dependent enzymes • With calcium binding domains called EF hands

• Nitric oxide (NO) is produced from arginine by NO synthase and activated by calcium ions. • It induces signaling cascades, such as the relaxation of the endothelial layer of arteries.

• ROS are major secondary signals. • At high concentrations, they can damage DNA and proteins, but they also serve in normal signaling.

• G-proteins and phospholipase C. • Protein kinases: Phosphorylate substrates, including serine PK and tyrosine PK. • Calcium-activated protein kinases: CDPK, calmodulin-activated CPK.

• Protein phosphatases catalyze the opposite reaction of protein kinases, removing phosphate groups. • They work in pairs with protein kinases, but usually only one is regulated.

• Activation or derepression of pathways. • Deactivation or repression of pathways. • Changes in enzyme activities, modulation of translation, transport processes, protein interactions, and chaperoning/ubiquitination.