Lecture Notes: Receptors and Cellular Communication

Introduction

• Cell Communication: Trillions of cells communicate in the body.
• Receptors: Proteins that receive information from outside the cell, functioning like sensory organs (eyes, ears, noses) for humans.

Types of Receptors

• Variety: Nearly a thousand different types of receptors.
• Active Sites: Highly specific to certain molecules or ligands (e.g., hormones).

Mechanism of Action

1. Ligand Binding:

   • Ligands bind to receptor's active site, causing a conformational change.
   • This change triggers a cellular response.

2. Signal Transduction:

   • Occurs when a receptor, a transmembrane protein, changes shape upon binding to a ligand.
   • This can result in the release or binding of substances inside the cell.

3. G-Protein Binding:

   • Activated receptors may bind to G-proteins on the inner plasma membrane.
   • G-protein activation can influence enzymes, leading to the release of second messengers like cyclic AMP.
   • Second Messengers: Molecules that amplify the signal within the cell.

4. Relay Molecule Release:

   • Conformational change may release relay molecules, starting a phosphorylation cascade.
   • This cascade exchanges phosphate groups, ultimately triggering a cellular response.

5. Receptor-Mediated Endocytosis:

   • Bulk absorption of substances through receptor clustering and vesicle formation.
   • Receptors return to the plasma membrane after delivering cargo inside the cell.

Intracellular Receptors

• Located within the cytoplasm or nucleus.
• Signal Molecule Requirements: Must pass through the plasma membrane (small, nonpolar molecules like nitric oxide).
• Functions:
  • Turn on genes by acting as transcription factors.

Cellular Responses

• Gene Regulation: Signals may turn genes on/off, affecting protein production.
• Metabolism Changes: Activation of enzymes like glycogen breakdown enzymes.
• Cell Division Regulation: Faulty receptors can lead to uncontrolled cell division and tumor growth.

Conclusion

• Receptors are essential for cell communication via hormones or neurotransmitters.
• Binding of these molecules induces structural changes in receptors, triggering reaction pathways and cellular responses.

• Further Learning: Future sessions will cover specific molecules triggering cellular responses.
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