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ATP hydrolysis: Gibbs free energy

How does ATP provide energy for biosynthesis reactions? Use an understanding of Gibbs Free Energy to understand how ATP is coupled to energy-requiring processes. By Jasmine Rana.

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Created by Jasmine Rana.

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  • blobby green style avatar for user eehartkopf
    May be worthwhile discussing G<0 as being "favored" or "spontaneous" vs G=0 as equilibrium vs G>0 as "unfavored" or "non-spontaneous" for completeness (maybe discussed in Gen chem section)
    (6 votes)
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    • blobby green style avatar for user merriken777
      Feel free to correct me if I'm wrong, but I believe the term "favorable" refers to being energetically favorable, a.k.a. the process does not use energy because it is spontaneous (G<0). "Unfavorable" means that energy is being used, and therefore the process is non-spontaneous (G>0). Ms. Rana did a video on Gibbs free energy without an emphasis on ATP that would help with understanding this.
      (10 votes)
  • male robot donald style avatar for user Christopher Michael GuanzOn
    Why is ATP preferred to be used as the energy currency of the cell than other nucleoside triphosphate?
    (4 votes)
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    • leafers sapling style avatar for user Peter Collingridge
      I don't think there's any real reason, it's just how life evolved. In fact other nucleoside triphosphates are used for some reactions. A molecule of GTP is generated by the citric acid cycle and is used to catalyse microtubule polymerisation and translation. UTP is used to drive the synthesis of glycogen from glucose. CTP is involved in glycosylation. Other phosphate carriers such as creatine phosphate, arginine phosphate and various inositol phosphates are also used a short term energy stores.
      (10 votes)
  • blobby green style avatar for user hcianci
    In previous videos, you've stated that Gibbs Free Energy has a unit of Joules/mol, but here it is stated that the unit is Joules. Which is correct or are they somewhat interchangeable?
    (5 votes)
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    • aqualine seed style avatar for user pinkmd
      This might be a little late but the units of Gibbs free energy is technically joules but it can be converted to joules/mol by using Avogadro's constant. You can confirm Gibbs free energy units by memorizing that the units for enthalpy is J, units for entropy is J/K and temperature is in K.
      (5 votes)
  • blobby green style avatar for user Anika Gupta
    I'm a little confused. In the previous video, He says that the -OH group of the water bonds to the Phosphate molecule and that the extra Hydrogen left over bonds to the ADP. But You say that the extra hydrogen becomes apart of another water molecule in the solution forming a hydronium ion. What gives?
    (3 votes)
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    • leaf green style avatar for user Hieronymus Bosch
      A hydrogen ion and a hydronium ion are both ways of saying that there's a free proton (or hydrogen ion) in the solution. Since the positive hydrogen ion is just a proton, it can bond with electrons like the lone pairs on the water molecule to yield the hydronium ion
      (1 vote)
  • leafers sapling style avatar for user Ashmita Pilania
    What exactly is energy?(please don't say it is the ability to do work)
    (2 votes)
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  • piceratops ultimate style avatar for user Firedrake969
    From an answer to a question on this page, there's A-, U-, G-, and CTP. Is that a coincidence that they start with the RNA bases?
    (1 vote)
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    • blobby green style avatar for user kira.premack
      Good question. It is not a coincidence! The A/U/G/C stand for the nitrogenous base that is part of the overall *TP molecule, and they are the same bases as are used in nucleotides like RNA. For ATP, the nitrogenous base is adenine. For GTP, it's guanine. For CTP it's cytosine, and Uracil for UTP. There is a good diagram of the structure that shows very clearly how the nitrogenous base is part of the overall molecule in the Overview of ATP hydrolysis article.
      (2 votes)
  • starky tree style avatar for user clarinsun
    Why is it that the conversion of a monomer to a polymer isn't a favorable reaction on its own (without the reaction coupling with ATP)? It seems to me that if you're making more bonds, the polymeric state should be more favorable and therefore make the conversion of monomers to polymers have a negative delta G.
    (1 vote)
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  • starky seedling style avatar for user Sofiya Smirnova
    Hello!
    How do you know that free energy (delta G) in the ATP hydrolysis is negative?
    (1 vote)
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  • blobby green style avatar for user zehrashahdr
    what are the conditions affecting to free energy in hydrolysis of ATP?
    (1 vote)
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  • blobby green style avatar for user isabella bennett
    Why can't organisms just use energy as soon as they get it without storing it in ATP?
    (1 vote)
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Video transcript

So let's talk about one of the most famous molecules in all of biochemistry, ATP. So why is ATP so famous? Well, it's the energy currency of the cell. And the reason it's called the energy currency of the cell is because it powers, it essentially fuels, many life sustaining reactions inside of our body. So some examples of these include biosynthesis of biomolecules. So remember fats, proteins, carbohydrates, and nucleic acids are all essential to life, and building these molecules requires energy in the form of ATP. In addition, ATP is also used to contract our muscles. And this is very important in order to allow living organisms to move. And additionally, ATP is also involved in some ion movement across cell membranes. And of course, moving ions across membranes is really important to maintain a comfortable internal environment within the cell. Now, you could take my word for it that somehow ATP magically powers all of these life-sustaining processes, but you really don't have to. In fact, in this video, we're going to review some topics from general chemistry to really understand how ATP, on a chemical level, really fuels these reactions. Now, the topic we want to review in introductory chemistry is a thermodynamic parameter called Gibbs free energy, or as it's more often written as just simply delta G. So now recall that delta G is a quantitative number. And it's a number that's measured in units of joules, which is a measurement of energy. And depending on whether this value is positive or negative, it tells us whether or not a reaction requires energy, or whether a reaction releases energy. Now remember that delta G is equal to the free energy of the products of a reaction, minus the free energy of the reactants in a reaction. So if the change in Gibbs free energy is negative, which means that the products have a much smaller free energy than the reactant, we say that this reaction releases energy. On the other hand, if we have a positive value of delta G, which means that our products are at a much higher energy level than our reactants, we say that that reaction requires an input of energy. And I know I've been kind of nebulous about this term energy here. And so, briefly, I want to remind you that the change in free energy going from reactants to products of a reaction takes into account both the change in enthalpy, as well as the change in entropy, which are two topics that you might be familiar with from general chemistry. So how does this all relate to ATP? Well, it turns out that there is a reaction involving ATP that has a very large negative delta G value. That is to say it releases a lot of free energy. Specifically, this reaction involves ATP combining with water, and when it combines with water, we call this a hydrolysis reaction. So I'll just write that here to remind us. And the products of this reaction are a molecule called ADP and a free phosphate group. And like I mentioned before, the change in Gibbs free energy is very negative. So what's going on here? So ATP starts out with triphosphate, three phosphate groups, loses a phosphate group because it becomes diphosphate. And then it forms a free phosphate group that it cleaved off. So on first glance, it might seem that this reaction is not balanced because we don't have this hydrogen or oxygen on the right side of our equation. But I just want to note here that the negatively charged hydroxyl group becomes a part of the phosphate group. And the remaining hydrogen ion of the water combines with another molecule of water in solution to become a positively charged hydronium ion. And usually, these two things are left out just for the sake of convenience. But I wanted to point them out here so that you wouldn't be confused by the stoichiometry. On the other hand, many biosynthesis reactions in the body have a positive delta G value. So remember, a positive delta G value means it requires an input of energy. And an example of this type of reaction is when we take a monomer, such as an amino acid for example, and we string them together covalently to form a polymer. So in the case of an amino acid, that would mean we're forming a long peptide chain. Now here's where our knowledge of introductory chemistry comes in. So in thermodynamics, the study of energy changes, there's an important principle that states that the overall delta G for a reaction-- I'm going to scroll down here to give us some more space. So the overall delta G for a reaction is equal to the sum of the delta G values for the individual steps of a reaction. So let's actually go ahead and add these two reactions together and see what happens. So let's write that out. So we have ATP as a reactant, as well as water, as well as our monomer subunits. And we are producing ADP, a free phosphate group, and a polymer. Now what is the delta G for our overall reaction? Well, we just simply have to add the delta G values for each step. Now I didn't give you actual numerical values for each of these steps. But in general, the hydrolysis of ATP produces energy in excess of the energy needed for biosynthesis reactions, such as this one. So essentially what I'm saying is that if we add a very large negative number to a smaller positive number, we will get an overall negative delta G value. In other words, we have just taken a previously energetically unfavorable reaction with a positive delta G value and turned it into an energetically favorable reaction with a negative delta G value. And we have done this by what we call coupling a reaction that has a favorable delta G value, such as the ATP hydrolysis, with a reaction that has an unfavorable delta G value. I want to mention that the ability to add these delta G values tells us nothing about the path that the reaction actually takes. And in fact, generally speaking, almost never does a reaction proceed in two discrete steps like it's written here. Instead, this coupled process often occurs simultaneously. But as you can see, it's still beneficial to separate these two reactions into two discrete steps, so you can prove to yourself essentially why ATP, with its negative delta G value, is able to fuel energetically unfavorable processes.