Phosphorylated nucleotides

What is ATP and why is it important in cells?

• ATP = adenine + ribose + 3 phosphate groups → a phosphorylated nucleotide.

• It is the universal energy currency used in all living cells.

• ATP is produced primarily during respiration.

• It releases energy for reactions such as:

  • Anabolic reactions (building molecules)

  • Active transport

  • Muscle contraction

  • Nerve impulse transmission

• Required by OCR A: ATP as the immediate source of energy in biological processes.

Describe the structure of ATP.

ATP consists of:

1. Adenine (nitrogenous base)

2. Ribose (pentose sugar)

3. Three phosphate groups bonded in a chain

• The bonds between the phosphate groups are high-energy bonds.

• ATP is a phosphorylated nucleotide (OCR keyword).

How do AMP, ADP and ATP differ?

• All contain adenine + ribose.

• Differ by number of phosphate groups:

  • AMP – 1 phosphate

  • ADP – 2 phosphates

  • ATP – 3 phosphates

• Adding phosphate groups increases the molecule’s potential energy.

What happens during ATP hydrolysis and why is it useful?

• ATP → ADP + Pi

• Catalysed by ATP hydrolase (ATPase).

• Energy is released when a phosphate bond is broken.

• Energy released is used immediately for:

  • Active transport

  • Muscle contraction

  • DNA/RNA synthesis

  • Metabolic reactions

How is ATP resynthesised?

• ADP + Pi → ATP

• Catalysed by ATP synthase.

• Occurs during:

  • Respiration (oxidative phosphorylation & substrate-level phosphorylation)

  • Photosynthesis (photophosphorylation)

• Requires an input of energy.

Why is ATP well suited to its role as the cell’s energy currency?

• Releases energy in small, usable amounts (prevents waste).

• Single reaction releases energy quickly.

• Immediate energy source—no long pathways needed.

• Easily regenerated by ATP synthase.

• Soluble, so can be transported around the cell.

• Can phosphorylate other molecules to make them more reactive.

How is ATP similar to DNA/RNA nucleotides?

• All contain a pentose sugar (ATP has ribose).

• All contain a nitrogenous base (adenine).

• All contain a phosphate group.

how is ATP different from DNA/RNA nucleotides?

• ATP has three phosphate groups, not one.

• ATP is used for energy transfer, not genetic information.

• ATP is a phosphorylated nucleotide.

State the main roles of ATP in living organisms.

• Metabolic reactions (anabolic + catabolic)

• Active transport

• Muscle contraction

• Cell signalling & nerve transmission

• DNA/RNA synthesis (phosphorylation makes nucleotides more reactive)

• Movement of vesicles and intracellular transport