Why Do We Need ATP for Endergonic Reactions in Metabolism?

[mktsgm]

This question might sound silly, but I think I am really missing some points about the energy requirements of metabolism. Please help me to understand better.

It is said that all catabolic (break down) reactions are inherently exergonic, ie., they release energy. Similarly, all anabolic (synthesis) reactions are endergonic, requiring energy for the reaction to take place.

1) If metabolism is the sum of all catabolic and anabolic reactions in the body, then why do we need the additional energy in the form of ATP (currency of energy) for endergonic reactions?

1.1) Are the catabolic and anabolic reactions not always mutually coupled?​

1.2) Is it the problem of storage of energy or conversion or utilization?​

1.3) Is ATP just an easier form of energy battery to store energy and use when needed?​

2) What is the form of the energy of ATP when it is released? Is it heat or some other medium? Is it related to the internal heat sensed by our body?

Thanks.

 

[Drakkith]

1) If metabolism is the sum of all catabolic and anabolic reactions in the body, then why do we need the additional energy in the form of ATP (currency of energy) for endergonic reactions?

ATP is not an energy source. It is a means of transferring energy. The source of the energy is the high-energy states of sugars, proteins, and fats that we eat. These are broken down into ATP and several other molecules that cells use to do a wide variety of functions, such as building molecules, molecular signaling, movement of cilia, excretion of wastes, etc.

Is ATP just an easier form of energy battery to store energy and use when needed?

Imagine you have a large storage tank in your back yard filled with gasoline and you want to fill a lawn mower, a generator, and number of other devices with gas so they can run. ATP is the plastic gas can that you fill from the larger tank that is then used to fill the gas tanks of everything around your house.

2) What is the form of the energy of ATP when it is released? Is it heat or some other medium? Is it related to the internal heat sensed by our body?

ATP is often used to facilitate a conformational change (shape change) in a larger molecule. For example, in muscle fibers, ATP binds to the head of a myosin molecule, unbinding it from an actin filament and allowing the myosin to change shape and move the head back into a position ready to rebind with actin during the power stroke phase of muscle contraction. The energy here takes the form of the motion of and potential energy stored in the myosin-actin system.

I'm unsure how much heat is generated from ATP reactions. It probably depends on exactly what the ATP is reacting with.

 

[morrobay]

I would say ATP is a potential chemical energy source because of the three negative charged phosphate groups bonded together. Energy can be transferred when this labile molecule disassociates.

 

[Hornbein]

Chemistry and biochemistry are different. In chemistry one heats up reactants in a flask so that they bump into one another with enough energy to elicit a change. The chemist might get 20 different reaction products and then have to separate out the one they want. That one might be only a tiny percentage of the total yield. Ouch.

Biochemical reactions are more like little machines. An enzyme may grab molecules A and B and put them together neatly to form then release molecule AB. There is for the most part only one possible result. It can be much more efficient than the heat in a flask method.

The enzyme does that by changing its shape. If the reaction is catabolic then the energy from the reaction can be used to change the enzyme's shape. Once AB has departed then the enzyme reverts to its original low-energy state.

If the reaction is anabolic then the enzyme has to actively push A and B together. It has to get the energy to do this from something like ATP. Once AB is formed and released both AB and the discharged ATP are released. The enzyme reverts to its original low-energy state and waits for A,B, and charged ATP to lodge onto it again.

Heat is released during all such operations, but that's because in this world net heat is released whenever anything happens. It's just waste.

By the way, I say that the true purpose of quantum computers is to enable chemists to design enzymes.

 

[morrobay]

 

[morrobay]

2) What is the form of the energy of ATP when it is released? Is it heat or some other medium? Is it related to the internal heat sensed by our body?

Thanks.

The Gibbs free energy ∆G, standard state, for ATP hydrolysis to ADP + inorganic phosphate = ∆G = ∆H - T∆S. ∆H enthalpy - 22kJ/mole , T is 298K and entropy ∆S is 22J/mole. So about -30.5 kJ/mole free energy ,∆G ,at standard conditions. Another equation is necessary for actually free energy taking into account concentrations.The ATP molecule has a very high negative charge density along the 3 phosphate groups. So when ATP disassociates the internal energy in the molecule that was required to overcome electrostatic repulsion can now be available for free energy in coupled reactions.