A small messenger like cAMP carries the signal inside
- The idea
- Predict
- See it
- Why
- Check
The idea
“The hormone, or its receptor, carries the signal into the cell.”
A hormone is called a messenger, so you picture it delivering the message in person. Many hormones can't even get through the membrane.
The short version
The mistake: The hormone, or its receptor, carries the signal into the cell.
What's actually true: When a hormone binds a surface receptor, a small molecule like cAMP, made inside the cell, carries the signal through the cytosol.
- The hormone is the first messenger. A polar one, like epinephrine, binds a surface receptor and never enters.
- The receptor and adenylyl cyclase stay in the membrane. Adenylyl cyclase makes the second messenger but doesn't carry it.
- A second messenger is a small molecule or ion, like cAMP or Ca2+, that spreads through the cytosol. One active enzyme makes many cAMP, which amplifies the signal.
On the exam: Look for the small molecule the cell makes inside, like cAMP. That's the second messenger.