2.3 - Energy and ATP

Question 1

What does ATP stand for

Answer 1

Adenosine triphosphate

Question 2

Describe the structure of ATP

Answer 2

• its a phosphorylated macromolecule, made of 3 parts:
  1. Adenine - a nitrogen-containing base
  2. Ribose - a pentose sugar, acts as the backbone to which the other parts are attached
  3. Phosphates - a chain of 3 phosphate groups

Question 3

How does ATP store energy

Answer 3

• the bonds between the phosphate groups are unstable and so have a low activation energy
• when they break, they release a considerable amount of energy (its usually the terminal phosphate that’s removed)

Question 4

Write out the equation for the release of energy from ATP

Answer 4

ATP (adenosine triphosphate) + H20 (water) —> ADP (adenosine diphosphate) + Pi (inorganic phosphate) + E (energy)

—> known as a hydrolysis reaction because water is used to convert ATP —> ADP
—> the reaction is catalysed by the enzyme ATP hydrolase (ATPase)

Question 5

Is the conversion of ATP to ADP reversible

Answer 5

Yes — its a reversible reaction

Question 6

What does the enzyme ATP synthase help with

Answer 6

• synthesis of ATP
  —> energy can be used to add an inorganic phosphate to ADP, re-forming ATP
  —> because water is removed, known as a condensation reaction

Question 7

How does the synthesis of ATP occur

Answer 7

involves addition of a phosphate molecule to ADP. Occurs in 3 ways
- in chlorophyll-containing plant cells during photosynthesis (photophosphorylation)
- in plant and animal cells during respiration (oxidative phosphorylation)
- in plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate-level phosphorylation)

Question 8

Why is ATP not a good long-term energy store, what’s the better ones

Answer 8

• bad = instability of its phosphate bonds
• fats and carbohydrates (like glycogen) is better
  —> therefore ATP is the immediate energy source of a cell
  —> therefore cells don’t store large quantities of ATP, instead: maintain a few seconds’ supply

Question 9

Why is ATP a better immediate energy source than glucose

Answer 9

• Each ATP molecule releases less energy than each glucose molecule. The energy for reactions is therefore released in smaller, more manageable quantities rather than glucose (larger, less manageable release of energy)
• the hydrolysis of ATP —> ADP is a single reaction that releases immediate energy. Whereas, the breakdown of glucose is a long series of reactions and therefore the energy release takes longer

Question 10

Why might cells such as muscle fibres or the epithelium of the small intestine require lots of mitochondria

Answer 10

• they require ATP
• ATP can’t be stored, so it has to be continuously made within the mitochondria of cells

Question 11

What energy-requiring processes in cells is ATP used in

Answer 11

• Metabolic processes: ATP provides the energy needed to build up macromolecules from their basic units. (E.g. making up starch from glucose/polypeptides from amino acids)
• movement: provides energy from muscle contraction. In muscle muscle contraction, ATP provides the energy for the filaments of muscle to slide past one another and therefore shorten overall length of a muscle fibre
• active transport: provides the energy to change the shape of carrier proteins in plasma membranes, allowing molecules/ions to be moved against a conc. gradient
• secretion: ATP is needed to form the lysosomes necessary for the secretion of cell products
• activation of molecules: the inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds in order to make them more reactive, thus lowering the activation energy in enzyme-catalysed reactions. (E.g. addition of phosphate to glucose molecules at the start of glycolysis)