Each stage of a cascade multiplies the signal
- The idea
- Predict
- See it
- Why
- Check
The idea
“Each stage of a cascade adds its molecules to the total, so 10 and then 10 makes 20.”
The stages come one after another, so adding them up feels natural. Each active protein actually starts its own branch of the next stage.
The short version
The mistake: Each stage of a cascade adds its molecules to the total, so 10 and then 10 makes 20.
What's actually true: Each stage multiplies the signal, so the output is the product of what every stage does.
- A protein kinase is an enzyme that adds a phosphate to another protein. One active kinase can switch on many copies of the next protein.
- So each stage multiplies the count before it. This is amplification. One epinephrine molecule can make a liver cell release millions of glucose molecules.
- Some steps pass the signal on one to one, like a G protein switching on one adenylyl cyclase. Count a step like that as × 1.
On the exam: Multiply the numbers from each stage of a cascade. Never add them.