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What is ATP?
What is the structure of ATP?
A phosphorylated macromolecule that has 3 parts:
- Adenine - a nitrogenous base
- Ribose - a sugar molecule with a 5-carbon ring structure that acts as the backbone to which the other parts are attached
- Phosphate - a chain of 3 phosphate groups
What is the function of ATP?
The main energy source to carry out processes within cells
How does ATP store energy?
- The bonds between the 3 phosphate groups are unstable and so have a low activation energy, meaning they are easily broken
- When the bonds do break, they release a considerable amount of energy
- Usually in living cells, it is only the terminal phosphate that is removed
How is ATP converted to ADP?
- A hydrolysis reaction that uses water, catalysed by ATP hydrolase
ATP + H₂O → ADP + Pi + Energy
How is ATP synthesised?
- Condensation reaction, catalysed by ATP synthase
ADP + Pi → ATP + H₂O
How does the synthesis of ATP occur?
- In chlorophyll-containing plants during photosynthesis (photo-phosphorylation)
- In plant and animal cells during respiration (oxidative phosphorylation)
- In plant and animal cells when phosphate groups are transferred from donor molecule to ADP (substrate-level phosphorylation)
Why is ATP not a good long term energy store?
Due to the instability of its phosphate bonds
Why do cells not store large amounts of ATP?
- Because it is the immediate energy source of a cell so cells just maintain a few seconds supply of it
- However, this is not a problem as ATP is rapidly re-synthesised from ADP and inorganic phosphate (Pi) and so a little goes a long way
Why is ATP a better immediate energy source than glucose?
- Each ATP molecule releases less energy than each glucose molecule so the energy for reactions is released in smaller, more manageable quantities rather than much greater, less manageable quantities of energy release from a glucose molecule
- The hydrolysis of ATP to ADP is a single reaction that releases immediate energy whereas the breakdown of glucose is a long series of reactions therefore the energy release takes longer
Why must ATP be continuously made within the mitochondria of cells that need it?
Because ATP cannot be stored
Why can't ATP be stored?
it is unstable and is low in energy density
What are the functions of ATP in energy-requiring processes in cells?
- Metabolic processes
- Active transport
- Activation of molecules
How is ATP used in metabolic processes?
- ATP provides the energy needed to build up macromolecules from their basic units
How is ATP used for movement?
- ATP provides the energy for the filaments of muscle to slide past one another and therefore shorten the overall length of a muscle fibre for muscle contraction
How is ATP used in active transport?
- ATP provides the energy to change the shape of carrier proteins in plasma membranes, allowing molecules or ions to be moved against a concentration gradient
How is ATP used in secretion?
- ATP is needed to form the lysosomes necessary for the secretion of cell products
How is ATP used in activation of molecules?
- Pi released during hydrolysis of ATP can be used to phosphoryate other compounds in order to make them more reactive
How is ATP a suitable energy store for cells?
- Releases relatively small amount of energy / little energy lost as heat
- Releases energy instantaneously/energy is available immediately
- Phosphorylates other compounds, making them more reactive
- Can be rapidly re-synthesised
- Does not leave cells
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