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Metabolism and Chemical bonds

  1. Sep 13, 2003 #1
    Recently, my Biology teacher was explaining about metabolism (unlike my other teachers, this one is a good teacher).
    He said : "catabolism produces energy on the form of ATP because it involves breaking chemical bonds".
    Now i feel a little confused about this.
    As far as i know, chemical bonds are there due to force(s) between atoms, and when you want to break a bond, you are taking the atoms apart from each other, in other words the direction of movement of each atom is in the opposite direction of the bonding force. From physics we would conclude that this (breaking the bonds) need energy and does not produce energy.
    Still, it is obvious that Catabolism produces energy, which makes the confusion for me.

    I tried to find a way out of this confusion, and this is what i reached :
    -To break the chemical bond, you actually need energy (only a confirmation to my previous conclusion)
    -When the certain bonds gets broken in the chemical compounds, new bonds will be formed (but not the same original bond)
    -In catabolism, the energy of the new bond (= the energy needed to break the new bond) must be more than the energy of the original bond, this way the difference of energies will make the whole proccess energy producive.

    Am i right or wrong ? If i am wrong please tell me how breaking bonds produces energy.
    Thanks in advance.
  2. jcsd
  3. Sep 13, 2003 #2
    You are wrong. Breaking a bond releases energy. It also takes energy to make a bond. Confused?

    Consider sugar. Plants take energy from the sun. They use it to make carbohydrates, bonding CO2 and water together. When we eat sugar, we break those bonds, releasing CO2 and H2O and energy. What do we do with the energy? We make a bond between ADP and inorganic phosphate. Then, when we're done eating and need energy again, we break the ATP back down again and we've got the energy back.

    Think of it as chemical potential energy. Sure, you never get the same amount of energy back, due to entropy, but since it al starts with the sun, we don't have to worry.
  4. Sep 13, 2003 #3

    But how would you explain that even though the bonding force is doing work against the movement of the atoms when breaking a bond, it will still release energy ?
  5. Sep 14, 2003 #4
    Consider a bond as a spring, vibrating very fast. Now cut the string, and the masses will go flying apart from each other, creating "useful work". It's not really the masses flying apart that does the work, but the heat released, or a redox reaction, or some other such thing. But you can still think of it as storing potential energy in a spring to be used later by breaking said string.
  6. Sep 14, 2003 #5


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    You are absolutely correct in your understanding and analysis of bond energies vs. REACTION energies. What you've run into is A difference (one of many) in the ways people in different scientific fields use same/similar words in different ways --- for the life of me, I don't know whether it's a deliberate technique to confuse the rest of the world, or not, but it is the way things have been for a long time.
    Again, you have stated a very good understanding --- energy HAS to be put into a bond to break it --- net energy release for a reaction is gained as a result of a subsequent bond formation process.[/QUOTE]

    Thanks in advance.

    Just bite your tongue in class, and learn your instructor's definitions for "bond, reaction, and energy."
  7. Sep 14, 2003 #6
    Now we have contradiction !
    I started a search on the internet, i found some sites that stated that energy is needed to break a chemical bond, and other stating that chemical bonds are a shape of potential energy.
    Eventually, i remembered that that wolfram research have a chemistry Encyclopedia, and i thought that most people on the forums would trust wolfram (The makers of Mathematica).
    I found Bond energy and Dissociation energy which both suggest that energy is released when chemical bonds are formed.

    A third opinion would be appreciated.
  8. Sep 14, 2003 #7


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    Ask CSF what he means when he says "cut;" I'd call it "adding" energy.
  9. Sep 14, 2003 #8
    It takes energy to cut a string, it takes energy to break a bond. If you cut a string you use scisssors, in biology you typically use a conformational change of an enzyme.

    Consider ATP as a boulder on a steep hill. It takes a lot of energy to get the boulder up the hill (making ATP from ADP). Now the hydrolysis of ATP is highly exothermic, it releases a lot of energy rolling down the hill. Now ATP is what they call metastable. It can just roll down the hill by itself, but the odds of that happening are small, practically for the organism. An enzyme comes along and nudges the boulder. It takes energy to move the boulder, the free energy of activation, is much smaller than the energy produced.
  10. Sep 15, 2003 #9


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    So basically you put in a little bit of energy just enough to 'push it over the edge' after which you gain more than you've put in.
  11. Sep 15, 2003 #10
    You gained more energy than it took to give it the nudge yes. But at some point in the past somebody had to push the boulder up the hill. So energy is still conserved.
  12. Sep 16, 2003 #11

    Another God

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    Re: Re: Metabolism and Chemical bonds

    Sorry for the slightly off topic post, but I couldn't let this one slide:
    I'd recommend against biting your tongue. If you ever don't understand or think the teacher is wrong etc, then I think you should be as vocal about it as possible until you are shown explicitly why you should accept what they are telling you.

    I am not sure whether it is better to perhaps wait until after class and ask in private so you don't interupt the class (the indoctrination of 'knowledge' to the mindless mass)m or whether you should interupt the class and ask hard questions, thereby perhaps causing other people to maybe think a little. Its a hard call, but whatever the answer, don't stop yourself from thinking about these things, and if something doesn't fit, say so.

    Good work.
  13. Sep 16, 2003 #12


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    Re: Re: Re: Metabolism and Chemical bonds

    Never be silent when you do NOT understand.

    Things may be different in Oz or in Jordan --- in the U.S. this is an excellent way to pick up a reputation as a troublemaker, smarta**, or get involved in a power struggle for control of a classroom --- rocks the boat. It's a "user's" call whether the instructor is open to correction/dialogue on topics, but, as a rule, not worth it --- hence, the advice (paraphrased) to learn what IS useful material presented in the classroom, sorting out the errors/chaff, and to also reply in the instructor's terms (errors and chaff) when interrogated.

    STAii is a sharp kid, and has been since he(?) showed up on these forums --- very pointed questions, not a lot of tangents, and the analytical skills to take HS level text/classroom presentations and see the holes that have been left in the arguments/developments of topics that interest him. Then he brings the questions here --- he's alluded once or twice to "conservative" approaches to teacher-pupil relationships, and that was what I had in mind when I suggested that he "bite his tongue" regarding the classroom line about "breaking bonds...release of energy."

    The kid's got the idea beautifully in hand ATP plus water vs. ADP plus phosphoric acid, break two bonds, make two bonds, and the energy of the reaction is the difference between the sums of the bond energies of reactants and products --- the bond energies are all attractive (release of energy on formation). He DOESN'T need to straighten out the misconceptions of everyone on the planet while he's still in HS(? No offense intended if I've misunderstood the point you've reached in your education, STAii). He's got much better things to do with his mind, and appears to be doing a damned good job of it without taking off on Quixotic quests against public education windmills. It IS really his call, and judgment, whether to initiate dialogues with instructors on the points he is continually finding and raising in these forums.
    Last edited: Sep 16, 2003
  14. Sep 17, 2003 #13
    Thanks all for your replies.
    Let me put you into the picture.

    About 7 years ago, 8 of the best teachers in Jordan (in different subjects) decided to start a project (to make more money i guess), that project was a school.
    When that school was built, they started to teach in it, and they hired other teachers too, they decided to teach the year 12 students (or so called Tawjihi in Jordan). But they were tricky, they decided to give scholarships for the best students in other schools to come and study for free in their school, and (of course), students were happy, since those 8 teachers were well-known.
    So, since they had the best students in their school, the best results of Tawjihi came from their school, and the school became famous. All people now wanted their children to study there, althought (as a student in that school) i can tell you it is not as good as it seems.
    Now (7 years later), this school is almost the biggest in Jordan (about 8000 students), and each year at least 3 of the 10 best-ranked students in Tawjihi (the year 12 exam) are from this school, and normally the first is one of those 3.
    Those teachers that originally founded it now think they are too good to do errors, they think they are some kind of the Gods-of-Tawjihi, and that they shouldn't and won't do any mistakes, and that they know everything.
    This is more like something they believe in (well most of them), and not something they can give up easily.
    Therefore, none of them accepts to be corrected, they don't accept any questions that are not included in the original textbook, and they can't admit being wrong.

    I have lot of examples:
    -I once asked my chem. teacher (while he was explaining about the continuous spectrum (sp?)) why the spectrum of a heated iron needle would be continuous (which is something he said), instead of answering me he started to ask me. He asked me "Why is the spectrum of the sun continuous", i answered what i believe was the right answer, and he started to ask and ask, and eventually, he didn't answer my original question.
    -The math teacher once was solving a limit problem (2 days ago), his answer was clearly wrong, i told him so, and tried to explain why, i was able to write 3 ways of prooving his answer was wrong, but he refused to listen to me. The next day he came saying that his answer was "inaccurate" (althought it was wrong, and not innacurate), and he said the reason was that his way of solving the question was too hard for the students (i wonder how this is related to the whole thing, he was solving the question alone, he could have chosen the way he wanted !).
    -My physics teacher once threatened me of "cutting my tongue" if i didn't stop asking questions. And once, when i asked him a question privately, instead of answering me he said (ironically) "Your ideas are good, i hope they will be useful for you in the Tawjihi exam", like and indirect way of saying that he expects a bad result from me in the exam. I still wonder, if i was asking him, why did he talk about my ideas ? It was not an idea, it was a question !

    Anyway, those are just some examples, the point is that the way my enviroment currently is, talking would only get me into more and more trouble, althought i personally think (in normal conditions) that the person should talk when he sees something wrong.

    Now back to the topic
    Knowing that my biology teacher wouldn't admit being wrong, i headed to my chemistry teacher.
    I asked him the question (in a main way, without showing its relation to metabolism), and he confirmed that energy would be needed to break a bond, and released when breaking a bond. Agreeing with the definitions from Wolfram.

    Your idea seems cool, It is true that cutting the string in your analogy will (in most of times) release more energy than needed to cut the string. But still, can you show how you reached the analogy between the string and the chemical bond, how are they alike ?

    Another God and Bystander
    Thanks for your care :smile:. I think i will not have a main idea of either trying to correct the teacher or not, i think the best is to look at each situation as a seperate case, sometimes i would be better to try to correct the teacher, and maybe sometimes it would just be worst (and a waste of time), althought i mainly think (as i said before) that correcting someone wrong is a good thing.

    Btw Bystander, i am a male. and :
    Well, it is the same in Jordan

    Thanks all. I guess i will have more questions coming with time.
    Last edited: Sep 17, 2003
  15. Sep 17, 2003 #14


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    Thanks for sketching your situation for us --- I don't know that it will improve the quality of any help we offer, but it gives us a context in which to understand the questions you bring to the forums.

    Sounds like you don't need advice from us on how to conduct yourself in class --- you're doing fine.
  16. Sep 22, 2003 #15

    jimmy p

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    Trying to answer

    Ok from what im trying to follow, you're thinking that catabolism would take energy instead of making energy.

    From what i can remember about my biology lessons, consider aerobic respiration for an example. The cells break down glucose into ATP but require ADP + P to break the glucose into 2 pyruvates etc. (boring biology bit) until all the ATP is produced. For every 1 ATP used up, 18 more are produced so yes catabolism requires energy, but the yield of produced energy is far greater
  17. Sep 23, 2003 #16
    I think you misunderstood me, i did not think that catabolism would take energy instead of making it.
    The only thing i was arguing about is the mechanism in which energy is made during catabolism.
    Anyway, everything is clear for me now.
  18. Sep 23, 2003 #17
    Actually, my favorite analogy for a chemical bond is two masses attached by a spring. It obeys simple harmonic motion and has a quantum mechanical equivalent of Hooke's law. There is a spring constant, a reduced mass, etc. This becomes very important in IR spectroscopy.
  19. Sep 23, 2003 #18


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    different viewpoint

    Staii, although you said you get the idea, I would just like to point out the role of ENZYMES in making these catalytic processes feasable.

    First one needs to understand two properties of enzymes:
    1. although an enzyme (a catalyst) participates in a reaction process, it stays UNCHANGED by it
    2. catalysts only change RATES of processes, they do not change the direction of equilibrium

    Now, I hope the following applies sufficiently to your question about breaking bonds.. otherwise it might be a good lesson by itself :)

    So let’s think in energy diagrams, a simplified catabolic reaction would start out in the initial state (reactants) at a HIGH FREE ENERGY (Ga) and the final state (products) at a LOWER FREE ENERGY (Gb). Obviously, such a reaction would occur automatically.

    But there is an intermediate state where there is a free energy barrier, energetic bonds need to be broken or conformations need to be changed – the concept of a TRANSITION STATE in the reaction. So here is the hill that chemicalsuperfreak was talking about.

    Now, a molecule can enter such a transistion state for instance by an energetic collision, once it is activated to the transition state, it can go either side of the barrier.

    Now, what a catalyst does is lower the energy barrier in a reaction, thus increasing the fraction of molecules that have enough energy to enter the transition state and make the reaction go faster. The equilibrium has not changed though! But if the concentration of the substrate is increased slightly, the reaction will tip.

    And how enzymes can do this feat, I know two models:

    LOCK AND KEY, where the reactant is brought together on the surface of the enzyme which fits nicely or the INDUCED FIT MODEL, where both enzyme and substrate are distorted upon binding, forcing it into the transition state. Once the substrate molecules have reacted, the enzyme will again change its conformation and bind new molecules.

    The enzyme Catalase, for instance, increases the uncatalyzed rate of H2O2 decomposition by about 1 billion-fold, without undergoing change itself.
  20. Sep 24, 2003 #19
    Actually, the energy diagram exactly expresses my idea.
    I am assuming you are talking about the energy diagram of the potential energy of molecules/atoms in the reaction.
    As it is obvious from the diagram, starting the reaction needs energy (i think this is something all the repliers agreed on), and starting the reaction is actually breaking (some of) the bonds in the reactants.
    What i was arguing about from the begining is whether or not breaking those bonds is actually the source of energy in catabolism.
    When the bonds are broken, we will actually be in the transition state (since it will be the highest point of potential energy), note that so far we needed energy.
    After the transition state the products start to form, now if the potential energy of the products is lower then the potential energy of the reactants, the whole process (=the reaction) will produce energy (therefore we conclude that in catabolism the potential energy of the products is lower than the potential energy of the reactants (as Monique said) since the reaction produces energy).
    Still, if the potential energy of the products is higher than the potential energy of the reactants, the whole proccess (=the reaction) will need energy (something not related to catabolism).
    Note that in both cases, the original bonds were broken.
    So, i conclude, that breaking the bonds does not produce energy, making them again is what produces the energy.

    Now, about enzymes, i understand enzymes will make the energy in the transition state lower, but will not change the (potential) energy of the reactants nor the products, therefore a reaction that needs energy will still need energy whether or not there was an enzyme, and a reaction that produces energy will still produce energy (the same ammount actually) whether or not there is an enzyme. So i guess my topic is a little more about chemistry than biology.

    My topic was only to know if i was right that the energy is produced while making the products of the reaction (iow, after the transition state) or before it.

  21. Sep 24, 2003 #20


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    I’d have to disagree.

    First I would have to say though, that energy is not produced or made, only converted. Normally the energy of breaking a bond would dissipate in heat..

    the cell utilizes this potential (free) energy by capturing it by coupling the release of free energy “-dG” (mainly heat) to an energetically unfavorable reaction (such as the formation of ATP out of ADP) so that it can be used at a later point in anabolism. Energy is lost in this system, not gained!!

    So I’d have to conclude that breaking bonds DOES release energy.. making them again DOES NOT produce energy. The point here IS that the energy type created in the second step is more usefull for the cell than the energy that was available in the first step.

    Just simply look at nuclear fission.. the amount of energy released by breaking bonds is very clearly demonstrated by the tremendous amount of heat that is released.
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