Biological Molecules: ATP

Question 1

ATP Structure & Function

Answer 1

• A single molecule of adenosine triphosphate (ATP) is a nucleotide derivative (modified form of a nucleotide)
- ATP is a nucleotide that acts as energy-carrier, capturing energy in some reactions and providing it for others

• ATP is formed from:

• a molecule of ribose
• a molecule of adenine
• three phosphate groups

Question 2

ATP Hydrolysis

Answer 2

• When energy is needed in a cell, ATP is hydrolysed into ADP (adenosine diphosphate) and Pi (inorganic phosphate)
• A phosphate bond is broken and energy is released
• This reaction is catalysed by ATP hydrolase

Question 3

ATP Hydrolysis: Coupling

Answer 3

• The hydrolysis of ATP can be coupled to energy-requiring reactions within cells

• Energy can be used directly to make the coupled reaction happen, rather than being lost as heat
• Energy-requiring processes are called endergonic reactions

Question 4

ATP Hydrolysis: Phosphorylation

Answer 4

• Hydrolysis of ATP releases an inorganic phosphate
• This inorganic phosphate can be bonded to other compounds to make them more reactive - this is called phosphorylation
• This happens to glucose at the start of respiration to make it more reactive

Question 5

Resynthesising ATP

Answer 5

• ATP is resynthesised by the condensation of ADP and Pi
- This reaction is catalysed by the enzyme ATP synthase during photosynthesis, or during respiration

• Energy from catabolism (the breakdown of complex molecules in living organisms to form simpler ones)
• Exergonic reactions, energy-releasing processes

Question 6

ATP Properties: Amount of Energy Released

Answer 6

• ATP release energy in small, managable amounts so no energy is wasted

• Cells do not over heat from wasted heat energy and are less likely to run out of resources
• Glucose releases larger amounts of energy that could result in wasted energy

Question 7

ATP Properties: Size

Answer 7

• ATP is small and soluble so it can be easily transported around the cell

• ATP can move around the cytoplasm with ease to provide energy for chemical reactions within the cell
• This is a property ATP shares with glucose

Question 8

ATP Properties: Hydrolysis

Answer 8

• Only one bond is broken/hydrolysed to release energy, which is why energy release is immediate

• One phosphate bond is broken
• Glucose would need several bonds to be broken down to release its energy

Question 9

ATP Properties: Phosphorylation

Answer 9

• ATP can transfer energy to another molecule by transferring one of its phosphate groups

• ATP can enable phosphorlyation, making other compounds more reactive
• Glucose cannot do this, as it does not contain phosphate groups

Question 10

ATP Properties: Availability

Answer 10

• ATP cannot pass out of the cell, the cell always has an immediate supply

• All cells have a constant supply of ATP or ADP and Pi
• Glucose can leave the cell and cells can run out of glucose