One bound molecule outside can change thousands of molecules inside the cell.

Circle one:   True   False

A ligand docks on a GPCR. What happens next inside the membrane?

• The ligand crosses the membrane alone to act inside
• The receptor changes shape and swaps GDP for GTP
• The second messengers leave the cell at once

Second messengers are hormones travelling in the blood to the cell. True or false?

Circle one:   True   False

What turns a GPCR pathway off?

• The ligand is used up when it binds the receptor
• GTP becomes GDP and messengers are cleared
• The receptor dissolves into the membrane

Where does the amplification in a GPCR pathway come from?

• The single ligand divides into many copies outside the cell
• The receptor copies itself many times in the membrane
• One receptor feeds several G proteins to many messengers

Epinephrine releases glucose from liver but quickens heart cells. Why?

• Same hormone meets different inner wiring
• Different hormones arrive at each cell type
• Stronger binding on the heart cells explains it

A toxin blocks the G protein from hydrolyzing GTP. What happens?

• The signal weakens but still shuts off normally on time
• The G protein sticks on and the signal never shuts off
• The receptor stops binding any ligand outside

The signal stops by itself once the ligand is used up. True or false?

Circle one:   True   False