Cell Signaling and Signal Transduction Quiz

Signal Transduction

• Signal transduction is the conversion of a signal from one form to another
• Communication relies on receptors, target cells, and extracellular signals
• Types of intercellular signaling include endocrine, paracrine, neuronal, and contact-dependent signaling
• Extracellular signals bind to cell-surface or intracellular receptors, which then activate intracellular signaling molecules
• G-protein-coupled receptors (GPCRs) activate G-proteins, which transmit the signal and then deactivate
• Three main types of cell-surface receptors are ion-channel-coupled receptors, G-protein-coupled receptors (GPCRs), and enzyme-coupled receptors
• Intracellular signaling pathways can lead to altered cell metabolism, cell shape/movement, or gene expression

Learning Objectives

• General principles of cell signaling and signal transduction
• Types of intercellular signaling
• Chemical nature of signal molecules
• Different responses of cells to same signal molecules
• Molecular switching mechanisms in signal transduction
• Signal transduction through various receptors

Lecture Outline

• Definitions
• General principles of cell signaling and signal transduction
• Types of intercellular signaling
• Chemical nature of signal molecules
• Different responses of cells to the same signal molecule
• Molecular switching in signal transduction
• Signal transduction through various receptor types

Definitions

• Receptor protein: a protein that recognizes and binds to a specific signal molecule, initiating a physiological response within the cell
• Extracellular signaling molecule: any molecule present outside the cell that elicits a response when binding to a receptor protein inside the cell
• Intracellular signaling molecule: a molecule that functions within the cell, acting as part of the mechanism for transducing and transmitting signals within the cell

General Principles of Cell Signaling

• Cell-cell communication is vital for both unicellular and multicellular organisms to coordinate behavior; it's essential for growth, development, differentiation, tissue & organ formation, maintenance of homeostasis, and diseases.
• An example of signaling is the fight-or-flight response, triggered by a signaling molecule like epinephrine.

Overview of Cell Signaling

• Signaling molecules (ligands) bind to specific receptor proteins.
• Reception sets off a relay team (proteins in the cell)
• Signal transduction occurs, leading to a cellular response. This response can include activating a gene, apoptosis, entering mitosis, etc.

Signal Transduction

• Converts information from one form into another
• Begins when a target cell receives an incoming extracellular (EC) signal and converts into intracellular (IC) signals, altering cell behavior

Examples of Signaling Molecules & Their Chemical Nature

• Signal molecules (e.g., epinephrine, cortisol, estradiol, insulin, testosterone, thyroid hormone) vary in chemical nature (e.g., amino acid derivatives, steroids, proteins)
• They originate in various locations (e.g., adrenal gland, ovary, pancreas, testis, thyroid gland)
• Depending on the location and chemical makeup some signal molecules elicit different results in various cell types.

Types of Intercellular Signaling

• Endocrine signaling: hormones released into the bloodstream to act on distant target cells.
• Paracrine signaling: local mediators act on nearby target cells.
• Neuronal signaling: neurotransmitters released across synapses to act on target cells.
• Contact-dependent signaling: transmembrane signal molecule binds to a receptor protein on a neighboring cell.

Two Classes of Signal Molecules

• Hydrophilic or large molecules relay on cell-surface receptors, similar to growth factors.
• Hydrophobic or small molecules activate enzymes directly or bind to intracellular receptors, such as steroid hormones.

Example: Steroid Hormones Signaling

• Hydrophobic nature allows steroid hormones to pass through the plasma membrane
• They bind to intracellular receptors
• The activated receptor-hormone complex moves into the nucleus and interacts with DNA to alter gene expression

Nitric Oxide Crosses the Plasma Membrane and Activates Intracellular Enzymes

• Nitric oxide (NO) is a small, unstable gas that crosses the plasma membrane.
• It activates enzymes directly, for example, to treat angina

Cell-surface Receptors Relay the Signal Through Intracellular Signaling Molecules

• Simple intracellular signaling pathway.
• Signal molecules bind to receptors, activating intracellular signaling molecules (e.g., kinases and G-proteins).
• This can impact cellular metabolism, shape/movement, or gene expression through a chain reaction

Common Intracellular Signaling Proteins

• Kinases (switches) activate/inactivate other proteins by phosphorylation.
• G-proteins (switches) bind GTP and are active, triggering signaling cascades

Why Molecular Switching is Important in Disease

• Bacteria toxins, like Cholera toxin, can alter G-proteins, causing catastrophic diarrhea/dehydration.
• Defective signaling pathways cause or contribute to various diseases.

Three Main Classes of Cell-Surface Receptors

• Ion-channel-coupled receptors
• G-protein coupled receptors (GPCRs)
• Enzyme-coupled receptors

Why is Signal Transduction Important

• Glycogen breakdown in skeletal muscle (fight-or-flight response)
• Rapamycin inhibits cell growth in cancer.