2.3 Energy and ATP

Question 1

Describe the structure of ATP.

Answer 1

It is a phosphorylated macromolecule with 3 parts:

• Adenine:organic base containing nitrogen
• Ribose: a sugar molecule with a 5-carbon ring structure that acts as a backbone
• Phosphates: Chain of 3 phosphate groups

Question 2

How does ATP store eergy?

Answer 2

• the bonds between the 3 phosphate groups are unstable so have a low activation energy, and are easily broken.
• when they break they release a lot of energy
• this is done by a hydrolysis reaction which converts ATP into ADP
• the reaction is catalysed by ATP hydrolase

Question 3

What is the equation of the reaction which releases energy from ATP?

Answer 3

ATP + H2O —> ADP + P + E

Question 4

How is ATP synthesised?

Answer 4

The conversion of ATP to ADP is reversible so energy can be used to add an inorganic phosphate to ADP to form ATP in a condensation reaction.

Question 5

What are the 3 ways an inorganic phosphate is added for the synthesis of ATP?

Answer 5

• In chlorophyll-containing plant cells during photosynthesis (photophosphorylation)
• In plant and animal cells during respiration (oxidative phosphorylation)
• In plant and animal cells when the phosphate is transferred from donor molecules to ADP (substrate-level phosphorylation)

Question 6

Why do cells not store large amounts of ATP?

Answer 6

• the instability of its phosphate bonds make it a bad long-term energy store, so it is the immediate energy source of the cell
• cells do not have large amounts of ATP, but a little goes a long way since it can be synthesised by the reverse reaction.
• it is continuously made within the mitochondria of cells that need it.

Question 7

Why is ATP a better immediate energy source than glucose?

Answer 7

• Each ATP molecule releases less energy than each glucose molecule, so energy is released in small, manageable quantities
• Hydrolysis of ATP to ADP is a single reaction which releases immediate energy. the breakdown of glucose is a series of reactions which takes longer.

Question 8

In which processes is ATP used?

Answer 8

• METABOLIC PROCESSES- ATP provides energy needed to build up macromolecules from their basic units. EG: making starch from glucose or polypeptides from amino acids.
• MOVEMENT- ATP provides the energy for muscle contraction, as it allows filaments to slide past each other and shorten the length of the muscle fibre.
• ACTIVE TRANSPORT- changes the shape of carrier proteins in plasma membranes which allows molecules to move against the concentration gradient.
• SECRETION- forms lysosomes necessary for secretion of cell products
• ACTIVATION OF MOLECULES- the inorganic phosphate released in the hydrolysis of ATP can be used to phosphorylate other compounds to make them more reactive, lowering the AE of enxyme-catalysed reactions.