MET - ATP [LESSON]

ATP

Adenosine Triphosphate

Adenosine triphosphate (ATP) is typically synonymous with “cellular energy.” 

 The image shows the ATP and ADP cycle with ATP labeled as the charged battery and ADP as the uncharged battery.

You can think of ATP and ADP as being sort of like the charged and uncharged forms of a rechargeable battery (as shown above). ATP, the charged battery, has energy that can be used to power cellular reactions. Once the energy has been used up, the uncharged battery (ADP) must be recharged before it can again be used as a power source. The “charger” is cellular respiration which will be discussed in the next lesson.

 Image shows structure of ATP with a 5 carbon sugar, an adenine nucleotide, and 3 phosphate groups connected.

The image above shows the chemical structure of ATP.  ATP is very angry and unstable because of its structure.  

Can you find the reason why ATP is so angry and unstable

The large amount of negative charges in the oxygens of the phosphate groups repel each other and so they want very badly to move further away from each other. 

Remember that it takes an input of energy to break any bond. This is even true for ATP.  The bonds between the phosphate groups in ATP do not require very much energy to break, but once they do, an exorbitant amount of energy is released as the whole molecule relaxes since the negatively charged oxygens are not pushed so far into each other anymore. Therefore, the conversion of ATP to ADP is extremely exergonic and is typically coupled with endergonic reactions to help them along.

Watch the ATP's Structure and Function video below to learn more about how ATP affects the energetics of an endergonic reaction.

How does ATP affect an endergonic reaction pathway?

The addition of ATP raises the free energy (G) of the reactants, making the overall pathway exergonic and spontaneous.

Energy Coupling

Reactions that are endergonic are non-spontaneous and cells must use energy to get them to proceed. In most cases, cells use a strategy called energy coupling, in which an energetically favorable (spontaneous) reaction (like ATP hydrolysis) is directly linked with an energetically unfavorable (non-spontaneous, endergonic) reaction.

 

Now, see what you know using the ATP Practice Quiz below.

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