What is the significance of time gap in the passage of action potenial from sino-arti node to the ventricle ?

What is the significance of time gap in the passage of action potential from sino-atrial node to the ventricle?

Passage of action potential from one node of Ranvier to the next is

What is the significance of atrioventricular node?

What is the significance of adding proteases at the time of isolation of genetic material (DNA) ?

What is the name of complex formed at the time of action of T-cells?