Cell Signaling Types and Stages

Types of Cell Signaling Molecules

• Endocrine ligands target distant cells through the bloodstream, e.g., hormones
• Paracrine ligands target cells near the original cell, e.g., neurotransmitters
• Autocrine ligands target themselves
• Contact-dependent ligands require direct membrane-to-membrane contact

Stages of Cell Signaling

• Reception: binding of signal molecule (ligand) to a receptor
• Transduction: conversion of the signal into a form that can bring about a response
• Response: change in behavior that occurs in the cell as a result of the signal

Reception

• Binding of a signal molecule (ligand) to a receptor is highly specific
• Conformational change in the receptor often initiates signal transduction
• Most signal receptors are plasma membrane proteins

Transduction

• Signal initiated by conformational change of receptors
• Process of activating a series of proteins inside the cell from the cell membrane, e.g., relay proteins and/or second messengers

Response

• Change in behavior that occurs in the cell as a result of the signal

Receptors

• Classified according to the type of ligands they bind
• Hydrophobic ligands (e.g., steroids, vitamin D3) bind to intracellular receptors
• Hydrophilic ligands bind to cell-surface receptors

Types of Cell-Surface Receptors

G-Protein Coupled Receptors (GPCRs)

• Receive a large number of signals from diverse groups
• Mechanism of action: ligand binds to receptor, activating G-protein, which activates enzymes and second messengers that carry out various functions

Tyrosine Kinase

• Ligand binds to the receptor, leading to dimerization of the kinase domains
• Phosphorylation of intracellular proteins allows them to bind and activate

Ion Channel

• Allow hydrophilic ions to pass through the plasma membrane
• Ligand binding opens the channel, e.g., neurotransmitters acting as ligands for Na+ ions

Signal Transduction Pathways

• Molecules relay a signal from receptor to response, usually proteins
• Signal transduction cascade: each protein activates the next, until the response is activated
• Protein Phosphorylation and Dephosphorylation: a cascade of protein phosphorylations (kinases) and dephosphorylations (phosphatases) acts as a molecular switch

Second Messengers

• Small, nonprotein, water-soluble molecules or ions
• Participate in pathways initiated by G-protein-linked receptors and receptor tyrosine kinases
• Examples: cyclic AMP (cAMP), ions, etc.

This quiz covers the different types of cell signaling molecules, including endocrine, paracrine, and autocrine ligands, as well as the stages of cell signaling, such as reception, transduction, and response.