YIJC [H2] CI3.3_Cell Signalling (N)(S)(vetted)

2025 JC2 BIOLOGY LECTURE NOTES CORE IDEA 3: ENERGY AND EQUILIBRIUM TOPIC 3.3: COMMUNICATION AND EQUILIBRIUM IN ORGANISMS (CELL SIGNALLING) Learning Outcomes: Candidates should be able to: Core Idea 3B: Communication and Equilibrium in Organisms (m) outline the main stages of cell signaling: (i) ligand-receptor interaction (ii) signal transduction (phosphorylation cascade and signal amplification) (iii) cellular response (change in gene expression) (Knowledge of intracellular receptors is not required) (n) explain the roles and nature of second messengers (including cyclic AMP) (o) explain the role of kinases and phosphatases in signal amplification (p) outline how insulin and glucagon regulate the concentration of blood glucose through the respective tyrosine kinase receptor and G-protein linked receptor. (The outline should be limited to describing how the ligand induces a conformational change in a membrane-bound receptor to trigger downstream signaling pathways that elicit physiological changes in blood glucose concentration. Details of different second messengers and specific kinases activated in the pathway are not required.) Use the knowledge gained in this section in new situations or to solve related problems. References: Reece, J. B. et al. (2018). Campbell Biology (11th Ed). Chapter 9: Cellular Signalling, pp. 214 – 231. H2

2 LECTURE OUTLINE: 1. Introduction 2. Types of Extracellular Signals 3. Stages of Cell Signalling 3.1. Stage 1: Ligand-Receptor Interaction (Reception of signal) 3.2. Stage 2: Signal Transduction 3.2.1 Second Messengers 3.2.2 Phosphorylation Cascade 3.2.3 Signal Amplification 3.3. Stage 3: Cellular Response 4. G-protein Linked Receptors (GPLRs) 4.1. Structure of GPLR 4.2. Regulation of Blood Glucose Concentration by Glucagon via GPLR 5. Receptor Tyrosine Kinase (RTK) 5.1. Structure of RTK 5.2. Regulation of Blood Glucose Concentration by Insulin via RTK 6. Advantages of Cell Signalling Pathways in Multicellular Organisms

3 1. Introduction ▪ Large multicellular organisms contain many different organs and tissue types. For all of these organs and tissues to work together as a unified whole, cell-to-cell communication is essential. ▪ Cells need to be able to receive and respond to extracellular signals. For e.g., communication between neurone and muscle cell for musc ular contraction, communication between cells of the endocrine gland and target cell for homeostatic control etc. 2. Types of Extracellular Signals ▪ Extracellular signals molecules fall into two classes. 1. The larger class of signals consists of molecules that are too large or too hydrophilic (i.e. polar OR charged) to pass through the cell surface membrane of the target cell (Relate this to the property of the phospholipid bilayer). This class of molecules relay their signals through the receptors embedded in the cell surface membrane of the t