3.1.6 ATP

ATP is the main energy source used to carry out processes within cells. It is a phosphorylated macromolecule with three parts:

• adenine (a nitrogen-containing organic base)
• ribose (a sugar molecule with a 5-carbon ring structure (pentose sugar) that acts as the backbone to which other parts are attached
• phosphates - a chain of three phosphate groups

The bonds between these phosphate groups are unstable so they have a low activation energy (this basically means they are easily broken down). When they break they release a considerable amount of energy - often only the last Pi (inorganic phosphate) is broken off. They are broken down by hydrolysis - the addition of water and the reaction is catalyzed by ATP hydrolase:

ATP + water --> ADP + Pi + energy

This is a reversible reaction meaning that energy can be used to add a Pi to ADP to reform ATP (this is the reverse to the reaction above). This reaction is catalyzed by ATP synthase. This is a condensation reaction and can occur in three ways:

• in chlorophyll-containing plants 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)

ATP roles:

Okay so this isn't in the spec but we did a lot about it in class so, let me know if you think it is useful for me to write about the roles of ATP/why it is good?