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Signal Transduction Pathway Overview

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About This MicroSim

This interactive diagram illustrates the complete signal transduction pathway from ligand binding at a G-protein-coupled receptor (GPCR) through the cAMP second messenger cascade to cellular responses including enzyme activation and gene expression changes. Students can explore 13 labeled structures across the three stages of cell signaling: reception, transduction, and response.

How to Use

  • Explore mode: Hover over any numbered marker or label to learn about that structure. The infobox below shows a detailed description and AP Exam tips for each component.
  • Quiz mode: Click the Quiz button to test your knowledge. Markers show "?" and you must click the correct structure when prompted.
  • Edit mode: Add ?edit=true to the URL to calibrate marker positions on the image.

Key Structures

Reception Stage

  1. Signal molecule (ligand) — The first messenger; binds specifically to the GPCR extracellular domain
  2. GPCR (receptor) — Seven-transmembrane receptor that undergoes conformational change upon ligand binding
  3. Cell membrane — Phospholipid bilayer barrier that prevents hydrophilic signals from entering the cell

Transduction Stage

  1. G-protein (inactive) — Heterotrimeric protein (Gα-GDP + Gβγ) docked on the membrane's intracellular face
  2. Active Gα-GTP subunit — Dissociated alpha subunit that activates adenylyl cyclase
  3. Adenylyl cyclase — Membrane-embedded enzyme that converts ATP to cAMP
  4. cAMP (second messenger) — Small diffusible molecule that activates PKA
  5. PKA (protein kinase A) — Enzyme that phosphorylates downstream targets
  6. Phosphorylation cascade — Sequential kinase activation providing exponential signal amplification

Response Stage

  1. Target enzyme (activated) — Final effector enzyme producing the cellular response
  2. Nucleus — Site of gene expression changes triggered by the signaling pathway
  3. Transcription factors — Proteins activated by phosphorylation that enter the nucleus to regulate gene expression
  4. Gene expression (cellular response) — Transcription of specific genes into mRNA, producing lasting cellular changes

Lesson Plan

Grade Level

9-12 (AP Biology)

Duration

10-15 minutes

Prerequisites

  • Cell membrane structure and selective permeability
  • Protein structure and enzyme function
  • Basic understanding of ATP and phosphorylation

Activities

  1. Exploration (5 min): Use Explore mode to trace the pathway from ligand to cellular response. Identify where amplification occurs at each step.
  2. Guided Practice (5 min): Discuss how the same ligand (epinephrine) can produce different responses in different cell types through the same GPCR-cAMP pathway.
  3. Assessment (5 min): Use Quiz mode to identify all 13 structures. Aim for a perfect score!

Assessment

  • Students can name and describe the function of each pathway component
  • Students can explain signal amplification at the G-protein, adenylyl cyclase, and kinase cascade steps
  • Students can distinguish between fast responses (enzyme activation) and slow responses (gene expression)

Iframe Embed Code

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