##Summary.

#Why ATP?

#Why not the alternatives?

#Efficiency and simplicity.

#Multi-functionality.

Summary.

Why ATP?

Why not the alternatives?

Efficiency and simplicity.

Multi-functionality.

When it comes to 'rebinding' the Pi to ADP, it is fairly easy since ADP seldom covalently binds to anything, which would require a lot of energy to recover the ADP. This also helps the bioavailability of free ADP to ATP synthase, an incredibly efficient enzyme, that uses membrane proton gradient to drive the production of ATP. Talking about actual numbers is difficult here as there is only data available from Rat hepatocytes. Who is to say mammals are representative of all organisms? The estimates of energy of hydrolysis range from ΔG˚ = -48 kJ mol-1 to -30.5 kmol-1. Note that these are considerable, but not exceptional values, so it's easy for many different proteins, that need not be very specialized, to break the bond all over the body. I couldn't even find the numbers for the synthase reaction per ATP, but a single ATP synthase can produce up to 600 ATP per minute.

When it comes to 'rebinding' the Pi to ADP, it is fairly easy since ADP seldom covalently binds to anything, which would require a lot of energy to recover the ADP. This also helps the bioavailability of free ADP to ATP synthase, an incredibly efficient enzyme, that uses membrane proton gradient to drive the production of ATP. Talking about actual numbers is difficult here as there is only data available from Rat hepatocytes. Who is to say mammals are representative of all organisms? The estimates of energy of hydrolysis range from ΔG˚ = -48 kJ mol-1 to -30.5 kJ mol-1. Note that these are considerable, but not exceptional values, so it's easy for many different proteins, that need not be very specialized, to break the bond all over the body. I couldn't even find the numbers for the synthase reaction per ATP, but a single ATP synthase can produce up to 600 ATP per minute.

• Alternative phosphate groups or other molecules may not provide enough energy.
• Alternatives may be toxic.
• Other molecules, particularly phosphates, are used for inefficient high energy bursts.
• ATP has ancestral dominance.
• Pi is a "good" leaving group.
• Phosphates are fundamentally able to be regulated through electrostatic manipulation.
• ATP synthase can efficiently reattach the Pi to ADP.
• Lots of Pi available to organisms because of it's ancestral dominance ("if it ain't broken, why fix it?" is at play).
• ATP can provide more energy if needed; it's scalable to the situation. (ADP becomes AMP + Pi)
• Easily usable by a variety of proteins.

• ATP has ancestral dominance. Most other reasons derive from this.

• Alternative phosphate groups or other molecules may not provide enough energy.

• Alternatives may be toxic.

• Other molecules, particularly phosphates, are used for inefficient high energy bursts.

• Pi is a "good" leaving group.

• Phosphates are fundamentally able to be regulated through electrostatic manipulation.

• ATP synthase can efficiently reattach the Pi to ADP.

• Lots of Pi available to organisms because of it's ancestral dominance ("if it ain't broken, why fix it?" is at play).

• ATP can provide more energy if needed; it's scalable to the situation. (ADP becomes AMP + Pi)

• Easily usable by a variety of proteins.