COURSE DESCRIPTION

The emphasis of this section is on how cell signalling processes can cause a physiological response in an organism. The circulatory system transports hormones from where they are secreted to the target cells. Hormones bind to specific binding sites – receptors found on the cell surface membrane or within the cell – to initiate the process of cell signalling.

Cell signalling comprises the following stages: ligand-receptor interaction, signal transduction and amplification, and cellular response. Various molecules such as second messengers, kinases and transcription factors mediate the processes of converting formation from the signal molecule (hormone) into a cellular response. Insulin and glucagon are examples of hormones that trigger cell signalling pathways to bring about responses to regulate blood glucose level.

It is important to appreciate the complexity and inter-connectedness of how the communication systems within and between cells interact to achieve the required response. The maintenance of blood glucose level will be used to illustrate how physiological responses are regulated by controlling gene expression. Sufficient glucose in the blood is necessary to provide cells with respiratory substrates. The pancreas detects the level of blood glucose and secretes either insulin or glucagon to maintain a stable level of glucose in blood. These hormones trigger cellular responses in liver, muscle and adipose cells when the hormones bind to receptors. Signal transduction occurs through various proteins and molecules to amplify and transduce the signal and eventually, elicit a cellular response. Thus, cell signalling and communication result in a relatively stable internal environment for cells in an organism to function optimally.

LEARNING OUTCOMES

Candidates should be able to:

From Core Idea 1:

(o) describe the molecular structure of the following proteins and explain how the structure of each protein relates to the function it plays:

iii. G-protein linked receptor (signalling)

(knowledge of details of the number of amino acids and types of secondary structures present is not required)

From Core Idea 3:

(m) outline the main stages of cell signalling:

1. ligand-receptor interaction
2. 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 signalling 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.

LECTURE NOTES OUTLINE

SECTION 1: CELL SIGNALLING

1. Introduction

• What is Cell Signalling?
• Three Stages of Cell Signalling: An Overview
  • Stage One Signal Reception
  • Stage Two Signal Transduction
  • Stage Three Cellular Response

2. Cell Surface / Membrane Receptor Signalling
   • Cell Surface / Membrane Receptors
   • Protein Phosphorylation and Dephosphorylation
   • Small molecules and ions as Second Messengers
   • Types of Receptors
     • G-Protein Linked Receptors (GPLR)
       • Cyclic Adenosine Monophosphate (cAMP): 2^nd Messenger in GPLR Signalling
       • Calcium ions (Ca²⁺) and Inositol Triphosphate (IP3): 2^nd Messenger in GPLR Signalling
     • Receptor Tyrosine Kinases (RTK)

CONCEPT CHECK 1

3. Advantages and Significance of Cell Signalling

• Signal Amplification
• Regulation of Cell Signalling
• Specificity of Cell Signalling

SECTION 2: HOMEOSTASIS – BACKGROUND READING

4. Introduction

• Why is there a need for Homeostatic Control?
• Homeostatic Control System
• Feedback Mechanisms

SECTION 3: ENDOCRINE SYSTEM

5. Introduction – Background reading

• What is the Endocrine System?
• Properties and Functions of Hormones
• The Pancreas and the Islets of Langerhans

6. Regulation of Blood Glucose Concentration
   • Blood Glucose Concentration is Regulated by Negative Feedback
   • Control Mechanisms in Regulation of Blood Glucose Concentration in Fed and Fasted States
   • Mechanism of Insulin – RTK Signalling (Supplementary)
   • Mechanism of Glucagon – GPLR Signalling (Supplementary)

CONCEPT CHECK 2

7. Diabetes Mellitus (Supplementary)