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What Is ATP's Phosphate Energy That Powers All Cellular Interactions?

  1. Aug 19, 2012 #1
    Hopefully someone can assist me here as i've searched the internet (google searches, wikipedia, youtube videos) in vain for this answer and yet i'm still stumped about just what is the actual ''energy'' being transfered from when after ATP leaves the ETC and then binds with a receptor (Organelles, DNA Transcription etc.) and releases it's high energy phosphate to then energize that cellular component. So what is actually inside that phosphate molecule? Is it transfering electrons?

    Thanks!
    Jess
     
    Last edited: Aug 19, 2012
  2. jcsd
  3. Aug 20, 2012 #2
    Yes, the general answer is moving electrons. Somewhere in the reaction there is a step where moving electrons, most probably from the phosphate, move an ATPase molecule that does work. However, the detailed answer involves physical chemistry.
    What you are asking is really a question about physical chemistry, rather than biology. The most general answer regards how energy is moved around in chemical reaction.
    When a chemical bond is broken, energy is absorbed as chemical potential energy. When a chemical bond is formed, chemical potential energy is released by changing it to some other form. The form the energy takes on release depends on the chemical reaction.
    One can visualize the process as chemical energy being first transformed into kinetic energy of the electrons in the bond. The electrons because of their electric charge move around the surrounding nuclei and electrons. So the energy gets turned into vibrational, rotational and translational kinetic energy of molecules. Because the electrons are electrically charged, moving around the electrons can also generate electromagnetic energy like light.
    Thus, chemical reactions absorb and release energy by the motion of electrons. The moving electrons drag the nuclei in the molecules around. For example, a proton can be moved in a direction against the electric field in a cell membrane. This results in electrical potential energy.
    The ATP molecule is connects temporarily with an ATPase, which is an enzyme that speeds up the decay of ATP. The bond between the adenosine and the phosphate is broken by absorbing some of the kinetic energy from the ATPase. The formation of bonds between the phosphate anion, the adenosine diphosphate cation and the ATPase releases energy that forces the ATPase molecule to move. The specific motion of the ATPase molecule then forces other molecules and ions to move in certain directions, absorbing most of the energy. The phosphate and the adenosine diphosphate disconnect from the ATPase molecule, absorbing most of the remaining energy.
    One example would be the proton pump molecules that exist in the cell membrane. In the case of a proton pump, ATPase, when the ATP loses a phosphate the ATPase is forced to spin. Thus, chemical potential energy in the ATP is turned to rotational kinetic energy in the ATPase. The spinning ATPase molecule forces a proton to move against a chemical gradient, or electric field. Thus, the rotational kinetic energy is turned into electrical potential energy.
    Different types of ATPase exist in the muscle cells, the nerve cells, and other cells. There are many such reactions known, and probably a lot that are unknown.

    http://en.wikipedia.org/wiki/ATPases
    “ATPase
    ATPases are a class of enzymes that catalyze the decomposition of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and a free phosphate ion. This dephosphorylation reaction releases energy, which the enzyme (in most cases) harnesses to drive other chemical reactions that would not otherwise occur. This process is widely used in all known forms of life.
    Some such enzymes are integral membrane proteins (anchored within biological membranes), and move solutes across the membrane, typically against their concentration gradient. These are called transmembrane ATPases.

    The ATP synthase of mitochondria and chloroplasts is an anabolic enzyme that harnesses the energy of a transmembrane proton gradient as an energy source for adding an inorganic phosphate group to a molecule of adenosine diphosphate (ADP) to form a molecule of adenosine triphosphate (ATP).
    This enzyme works when a proton moves down the concentration gradient, giving the enzyme a spinning motion. This unique spinning motion bonds ADP and P together to create ATP.
    ATP synthase can also function in reverse, that is, use energy released by ATP hydrolysis to pump protons against their thermodynamic gradient.”
     
  4. Aug 20, 2012 #3

    Drakkith

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    Staff: Mentor

    I think this also requires an understanding of what energy is according to physics. In its basic definition energy is simply the ability to perform work. Work is the result of a force acting on an object, causing a displacement at the point of interaction. You could say work is change in a system.

    Please understand that energy is NOT some mystical "substance" that gets moved around. If an electron is accelerated by an electric field it gains energy in the form of kinetic energy. The electron is not carrying a blob of energy with it now that it is moving, it is the movement of the electron itself which we define to have energy since that electron can now perform work on another charged particle if it interacts with it.

    Because keeping track of particles and objects and forces can get complicated when talking about a complex system, it is very useful to have the concept of "energy" when we just want to talk about the input and output of something such as a machine, a cell, or a chain of chemical reactions.
     
  5. Aug 21, 2012 #4
    This requires understanding the concept of spontaneity and free energy.

    Chemical reactions are spontaneous i.e. they happen on their own when the reaction releases free energy, called Gibbs Free energy represented by ΔG. This is mathematically defined as

    ΔG=ΔH-TΔS,
    where ΔH is change in enthalpy (can be loosely equated to energy)
    ΔS is change in entropy (can be loosely called the amount of order)
    T is Temperature

    Therefore for spontaneity, ΔG should be negative (release) and not positive (absorption).

    Note that like Drakkith said, when we talk about energy being released we don't mean a sphere of glowing and shining energy coming out of the molecule, but instead the energy manifesting itself in the environment i.e. making other surrounding molecules move faster (heat).

    Now there are many reactions that happen in a cell. Many of them are energetically favourable (release free energy) but are very slow (due to large activation energies) so enzymes act as catalysts to speed them up (lower activation energy by providing an alternate reaction path). However they cannot force energetically unfavourable reactions where ΔG is positive (call endergonic reactions). In such situations cells make these reactions by happen by coupling them to another highly exergonic reaction (where ΔG is very negative) via a shared intermediate or ATPases so that the overall ΔG is negative. In biological systems this exergonic reaction is ATP hydrolysis (ATP --> ADP + Pi). NOTE: Not to be confused with Coupling Reaction

    You can visualize coupling in a mechanical system. Now suppose we have to raise a bucket of water to a certain height. The bucket won't rise on it's own of course since that will increase it's potential energy (analogous to an endergonic reaction). Water falling from a great height (in a water fall) has a lot of kinetic energy (our exergonic process). If we attach a rope to the bucket and the other end to a turbine which is kept under the waterfall, the spinning turbine will raise the bucket. Something similar happens in chemical systems as well.

    BTW Drakkith you might want to change your sig so that you don't confuse people :wink: :biggrin:
     
  6. Aug 21, 2012 #5

    Drakkith

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    Staff: Mentor

    Buahaha!
     
  7. Aug 21, 2012 #6
    Thanks a million to Darwin, Drakkith and Mishrashubham as i really appreciate your well written detailed answers as i was growing frustrated with empty searches to this perplexing biochemical reaction until i stumbled across this site and intuitively figured that someone(s) on here would know the answer. Lol, now i can sleep better tonight :wink:

    Again thank you!!

    Jess
     
  8. Aug 21, 2012 #7
    You're welcome :smile:
     
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