C.2.1 · 化学信号传导

What would explain this observation?

• Two cell types encounter the same signal but respond differently. Their receptors and internal pathways determine what follows.
• Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.

Build the model

• A signalling molecule binds a compatible receptor. Receptor activation can initiate signal transduction 信号转导 through intracellular molecules. The resulting response may change enzyme activity, transport or gene expression. A signal need not enter the cell to cause an effect.
• receptor: A molecule that binds a compatible signal; signal transduction: Conversion of signal reception into intracellular changes.

Choose evidence that can test it

• Distinguish signal reception, transduction and response. Amplification can allow a small extracellular change to produce a larger intracellular effect. Different receptors or pathways can give different responses to one signal.
• Use an attributed dataset comparing signal concentration and response. Include an untreated control and, where supplied, receptor-blocking evidence. Do not infer the whole pathway from a concentration-response graph alone.

Work from known quantities

• State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
• Known: response increases from 20 to 80 units. Fold change = 80/20 = 4. Percentage increase = (80−20)/20 × 100 = 300%. A fourfold final value is not a 400% increase.

Example:

Response rises from 10 to 50 units. Calculate the fold change. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.

Check the conclusion and its limits

• A receptor is not interchangeable with every signalling molecule. Greater signal concentration does not imply unlimited response once the system saturates.
• Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.

Warn:

Fourfold final response means a 400% increase from baseline. This claim is false: A receptor is not interchangeable with every signalling molecule. Greater signal concentration does not imply unlimited response once the system saturates.

Key:

Cell signalling: a receptor selects the response: Distinguish signal reception, transduction and response. Amplification can allow a small extracellular change to produce a larger intracellular effect. Different receptors or pathways can give different responses to one signal.