Cell Signal Transduction - Week 5

Cell Signal Transduction Prepared by Dr Abdulrahman Aljabri Expected to learn Be the end of this session, students should be able to: Define the cell signal transduction List types of cell signalling Describe the different chemical forms of cell signalling Define the receptor and lig...

Cell Signal Transduction Prepared by Dr Abdulrahman Aljabri Expected to learn Be the end of this session, students should be able to: Define the cell signal transduction List types of cell signalling Describe the different chemical forms of cell signalling Define the receptor and ligands List different types of receptors and how they involved in cell signalling Describe the second messenger e.g. cGMP Cell Signal transduction Cell Signal transduction: - Is the process by which a cell responds to external chemical signals. - It is crucial for cellular communication and regulation of various biological processes. Cell signalling’s types: 1. Intercellular signalling: Communication between cells. 2. Intracellular signalling: Signalling chains within the cell, responding to extracellular and intracellular stimuli. Intercellular signalling: In Eukaryotic, intercellular signalling coordinates vital functions, ensuring the maintenance and function of specialized tissues and organs: Cell growth Cell division Cell motility Cell morphology Signalling Receptors Receptors are protein molecules in or on target cells that bind to ligands, initiating a cellular response. Ligand A ligand is a molecule that attaches to specific receptor Receptor on a cell to trigger a biological response and this connection sends a message or signal. Ligands act as "keys" that bind to "locks" (receptors) on the cell A specific ligand will have a specific receptor that typically binds only that ligand. Receptors are essential for cell communication and response. Intercellular signaling: Steps of Intercellular Signaling: 1. Formation: An external trigger causes the production/release of signaling molecules (e.g., hormones) from specialized cells. 2. Signal Transport: The signal travels to the target cell, often via circulation or diffusion, sometimes with carrier proteins. 3. Signal Reception: The target cell receives the signal through specific receptors, initiating intracellular signaling pathways. 4. Signal Processing: The signal is converted into a biochemical response within the target cell, leading to specific cellular actions.  Stages of cellular signal transduction 1. Reception 2. Transduction 3. Response Cells detect chemical signals The signal is converted into The cell performs a specific through receptors. an internal response. action in response to the signal. Ligand binds to receptor. Signal Pathways: Often involve a series of steps with Action: Could include changes Receptor changes shape, relay molecules. in gene expression, enzyme activating the cell. activity, or cell metabolism. e.g. Protein Kinases: Add phosphate groups to proteins, e.g. Cell division, muscle amplifying the signal. contraction, or apoptosis (programmed cell death).  Forms of chemical cell Signaling Cells communicate through extracellular signaling molecules that bind to receptors on target cells, triggering a response. Depending on the distance the signal travels; There are four forms of chemical cell signalling: 1) Paracrine 2) Endocrine 3) Autocrine 4) Direct signalling across gap junctions. Forms of chemical cell Signalling 1. Paracrine Signaling Signals act locally between nearby cells. Signals move by diffusion through the extracellular matrix. Elicit quick, short-lasting responses. https://openoregon.org Forms of chemical cell Signalling 2. Endocrine Signalling Signals originate from distant endocrine cells. Located in endocrine glands like the thyroid, hypothalamus, and pituitary. Produce slower, longer-lasting effects. Hormones are released by glands into the bloodstream, where they travel long distances to target cells in different parts of the body. Forms of chemical cell Signalling 3. Autocrine Signalling Signals produced and responded to by the same cell or similar cells. Signaling cell releases a signal that binds to its own receptors. Ensures proper tissue formation and function during early development. Forms of chemical cell Signalling 4. Direct Signaling Across Gap Junctions Direct communication between neighboring cells through water-filled channels. Gap junctions in animals, plasmodesmata in plants. Small molecules like calcium ions (Ca2+) can pass through; larger molecules cannot.  Types of receptors 1. Internal Receptors Internal receptors, found in the cytoplasm or nucleus. Respond to hydrophobic ligands that cross the plasma membrane. These receptors regulate gene expression by binding to DNA after a ligand- induced conformational change. 2. Cell-Surface Receptors Cell-surface receptors, or transmembrane receptors, bind external ligands without the ligands entering the cell. These receptors are specific to cell types and convert extracellular signals into intracellular actions. Types of Cell-Surface Receptors 1. Ion Channel-Linked Receptors These receptors open a channel through the membrane when a ligand binds, allowing specific ions to pass through and alter the cell's activity. E.g. acetylcholine (nicotine receptor) Types of Cell-Surface Receptors 2. G-Protein-Linked Receptors These receptors activate G-proteins upon ligand binding, which then interact with other membrane proteins to propagate the signal. G-proteins switch between active and inactive states to regulate cellular responses. E.g. Dopamine Types of Cell-Surface Receptors 3. Enzyme-Linked Receptors These receptors have an intracellular domain that acts as an enzyme or associates with an enzyme. Ligand binding activates the enzyme, triggering a cascade of cellular events. E.g. insulin receptor Examples of common events in intracellular signalling 1. Phosphorylation: Adding a phosphate group to a protein by an enzyme called kinase, which can activate or deactivate the protein. 2. Second Messengers: Intracellular, diffusible small molecules and ions that are quickly synthesized or released in response to signals from receptors, altering the activity of target signalling proteins.  Second Messengers (examples) Cyclic nucleotides: Lipid messengers: Cyclic adenosine monophosphat originate within cell e (cAMP) membranes Cyclic guanosine Inositol trisphosphate (IP3) monophosphate (cGMP) Gases : can signal throughout Ions: signal within and the cell and even to between cellular neighbouring cells compartments NO Calcium (Ca) CO Na and K Hydrogen sulphide (H2S)  cGMP (Cyclic guanosine monophosphate) Structure: Nucleotide with a sugar, guanine base, and a single phosphate group in a cyclic bond. Function: acts as a second messenger in processes like: - Smooth muscle contraction - Phototransduction in the eye - Blood vessel dilation Second Messengers | Concise Medical Knowledge (lecturio.com) Reference of figures: HTTPS://OPENOREGON.ORG BIOCHEMISTRY OF SIGNAL 2014 WILEY-VCH VERLAG GMBH & CO. TRANSDUCTION AND REGULATION, KGAA. PUBLISHED 2014 BY WILEY-VCH FIFTH EDITION. GERHARD KRAUSS VERLAG GMBH & CO. KGAA.