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6.4 ATP: Adenosine Triphosphate
Even though living things are highly ordered and maintain a state of low entropy, the universe's total is constantly increasing due to losing usable energy with each energy transfer that occurs.
Living things are fighting a constant increase in universal entropy.
A measure of randomness is entropy.
Gases and liquids have higher levels of entropy.
By the end of this section, you will be able to explain the role of the cellular energy currency.
Their products have more free energy than their reactants, so endergonic reactions need more energy input.
This is a relatively simple molecule that has the potential for a quick burst of energy that can be used to perform cellular work.
Money is the currency that people exchange for things they need, and this molecule is the primary energy currency of the cells.
The majority of energy-requiring cellular reactions are powered by ATP.
The cell has a primary energy currency.
There are three groups attached to it.
adenosine triphosphate is comprised of adenosine bound to three groups.
A five-carbon sugar, ribose, and a nitrogenous base adenine make up a nucleoside.
The ribose sugar has three phosphate groups in order of closest to it.
The chemical groups are an energy powerhouse.
Some bonds within this molecule are not in a high-energy state.
The second and third bonds are between the first and second groups.
The products of such bond breaking have a lower free energy than the reactants.
The reaction takes place using a water molecule.
It is like most chemical reactions.
The reverse reaction can be used to regenerate ATP.
People rely on regenerating spent money through some sort of income.
The free energy must be input into the regeneration process.
There are two important questions regarding the use of ATP as an energy source.
One would expect a different value to exist under cellular conditions since this calculation is true.
The molecule is unstable.
The free energy released during this process is lost as heat unless quickly used to perform work.
The second question is about how the energy release works inside the cell.
This depends on a strategy.
The cells couple the reaction.
A transmembrane ion pump is very important for cellular function and is an example of energycoupling using ATP.
The Na+/K+ pump is used to drive sodium out of the cell.
The pump is powered by a large percentage of a cell's ATP, which is brought into the cell by cellular processes.
The pump works to keep cellular concentrations stable.
One ATP molecule must hydrolyze in order for the pump to turn one cycle.
When ATP hydrolyzes, it actually transfers itsgammaphosphate onto the pump.
Scientists call this process of binding a phosphate group to a molecule.
The Na+/K+ pump undergoes a conformational change when it is phosphorylated.
Na+ can be released to the cell's outside.
The binding of extracellular K+ causes thephosphate to detach from the pump.
The K+ is released to the cell's inside.
The energy released from the ATP hydrolysis couples with the energy required to power the pump and transport Na+ and K+ ionized water.
This basic form of energy is used to perform cellular work.
An example of energycoupling is the sodium-potassium pump.
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