Question

What is the structural difference between ATP and ADP?

Answer 1

The clue is in the names!

Adenosine `"tri"`phosphate, and

Adenosine `"di"`phosphate

ATP has three phosphate groups, whereas ADP has two phosphate groups on its ribose sugar.

The removal of the phosphate group via ATP hydrolysis releases approximately `40"kJ"` of energy, and is frequently coupled with endergonic biological reactions,

`ATP to P_"i" + ADP`

Answer 2

Just one phosphate group.

Explanation:

Adenosine triphosphate, `"ATP"`, has three phosphate groups, hence the name with "tri-".

Adenosine diphosphate on the other hand, `"ADP"`, has only two phosphate groups, and so has the prefix "di-".

So, `"ATP"` has one extra phosphate group than `"ADP"`.