More Biological Molecules - ATP

Question 1

What is ATP?

Answer 1

The immediate source of energy in a cell.

Plant and animal cells release energy from glucose
– this process is called respiration.

So, in respiration, the energy released from glucose is used to make ATP (adenosine triphosphate).

Once made, ATP diffuses to the part of the cell that needs energy.

The energy in ATP is stored in high energy bonds between the phosphate groups.
It’s released via hydrolysis reactions.

Question 2

What is ATP made up of?

Answer 2

ATP is made from

• the nucleotide base ADENINE, combined with
• a ribose sugar and
• three phosphate groups.

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It’s what’s known as a nucleotide derivative because it’s a modified form of a nucleotide.

Question 3

How is ATP made and used?

Answer 3

When energy is needed by a cell, ATP is broken down into ADP (adenosine diphosphate) and Pᵢ (inorganic / single / lone phosphate).

This is a hydrolysis reaction.
A phosphate bond is broken and energy is released.
The reaction is catalysed by the enzyme ATP hydrolase.

ATP hydrolysis can be ‘coupled’ to other energy-requiring reactions in the cell – this means the energy released can be used directly to make the coupled reaction happen, rather than being lost as heat.

The released inorganic phosphate can also be put to use –
it can be added to another compound
(this is known as phosphorylation),
which often makes the compound more reactive.

ATP can be re-synthesised in a condensation reaction between ADP and Pᵢ.
This happens during both respiration and photosynthesis,
and is catalysed by the enzyme ATP synthase.

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IN SHORT:

ATP means three Ps
ADP means two Ps
Pᵢ is one single, lone P

SO

ATP undergoes HYDROLYSIS
with enzyme ATP HYDROLASE
ENERGY IS RELEASED
and forms ADP and Pᵢ

AND

ADP and Pᵢ undergo CONDENSATION
with enzyme ATP SYNTHASE
ENERGY IS USED
and forms ATP