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How do inactive enzymes act?

  1. Apr 19, 2012 #1
    enzymes are considered inactive at low tempertaures, and denatured at high temps.both these terms have different meanings, with inactive meaning enzyme having "low activation energy"and denatured meaning the enzyme is destroyed.
    when an enzyme is inactive, it does not lower the activation energy of a chemical reaction, and it does not react with the substrate. i am not exactly sure how the enzyme lowers the activation energy of the chemical reaction, so i am actually guessing that there is no form of lowering of activation energy when the temp is very low.please correct me if i am wrong. according to my bio teacher, she claims that an inactive enzyme has low activation energy and this can be explained using the collisive particle theory. so i am again assuming that what she meant was when the temp is too low, rate of reaction is low as the enzyme molecules are unable to lower the activation energy hence it takes a longer time for the chemical reaction to occur as the enzyme and substrate molecles need more energy to have sufficient activation energy for the chemical reaction to occur.
    is my theory correct?

    and, can someone please explain to me what it means exactly for an enzyme to be inactive, does it just purely mean that it doesnt react with the substrate? enzyme cannot be inactive at high temps right? it is denatured, right?

    help is really appreciated thanks!
  2. jcsd
  3. Apr 19, 2012 #2
    Enzymes effectively bind to the transition state of a reaction and putting the reactants in a favorable position to react. When the temperature is low, it merely means there either isn't enough kinetic energy in the system for the reaction to occur or the movement of the reactants themselves is hindered to the point where they don't bind nearly as much.

    It depends on the temperature and the enzyme itself, as some are more stable at higher temps than others, but generally yes, enzymes will denature at high temps and since function is directed by structure, the enzyme becomes useless.
  4. Apr 19, 2012 #3


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    Chemical reactions occur when the reactants collide with enough energy for bonds to start breaking and rearranging. The minimum amount of energy required for the collision to result in a reaction is known as the activation energy. Enzymes lower the activation energy of reactions, for example, by helping the reactants collide in the correct orientation or by placing strain on one or more of the reactants so that its bonds are more easily broken. By lowering the activation energy of a reaction, the enzyme speeds up the rate of the reaction.

    Of course, activation energy is not the only factor that determines the rate of a chemical reaction. The energy of the collisions that leads to chemical reactions depends on the temperature of the solution: the warmer the solution, the more energetic the collisions. Conversely, if the temperature is too low, very few molecules in solution will carry enough thermal energy to provide the activation energy for a chemical reaction. Even if an enzyme is present, the chemical reaction will proceed very slowly if there isn't enough thermal energy available.

    When we say an enzyme is inactive, we just mean that we can't see the enzyme catalyzing a certain reaction (or the enzyme is catalyzing the reaction very inefficiently). There are many things that can cause an enzyme to be inactive. If the temperature is too low, the reaction will proceed very slowly and the enzyme will appear inactive. However, denatured enzymes also cannot function properly to lower the activation energy of a reaction. Therefore, denatured enzymes are also inactive.
  5. Apr 20, 2012 #4
    huh but my bio teacher said that denatured and inactive are two different meanings!

    had my bio test today, was a killer paper.i only knew how to do one question.>.<
    there was a confusing graph showing the decrease of lactose concentration with time, with the concentration of the enzyme lactase being a fixed factor. from the graph, we are supposed to deduce the rate of reaction in relation to the substrate concentration . how am i supposed to answer this? i put that the rate of reaction is increasing, some others said it was increasing at a decreasing rate, increasing then decreasing, or just decreasing. sol which exactly is the answer? please help thanks!
  6. Apr 20, 2012 #5
    Enzymes can be inactivated through a wide variety of means, beyond just denaturing the enzyme. One can have an inhibitor bound to the enzyme, a critical residue for catalytic activity can be covalently modified, an allosteric mechanism for enzyme function could be at work, and so on.

    Denaturation of a protein refers to the loss of its three-dimensional tertiary structure. This can be done through high temperature, although it can also be done through chemical means (high concentrations of urea or guanidine). There is even "cold denaturation," where cold temperatures induce the loss of a protein's tertiary structure.

    While there is a connection between these concepts, one cannot say that all inactive enzymes are denatured.

    Without the actual graph in front of me, I would not dare to venture a guess. However, you might find


    to be useful/educational.
  7. Apr 20, 2012 #6
    Are you pointing out my typo?

    Edit: Ah, I see. If any moderators see this, guistra199 is a spammer for Infoocean . info. All of his posts are automated mimics of somebody else's post, but with an invisible hotlinked image that counts toward their traffic. I've seen the same thing on another forum I frequent.
    Last edited by a moderator: May 5, 2017
  8. Apr 21, 2012 #7
    I always considered inactive to be a general term, and to mean that an enzyme simple doesn't catalyse a reaction. I suppose saying an enzyme is inactive can encompass 'deactivated' enzymes, non-functioning (e.g. through mutation) enzymes or zymogens. Denatured enzymes aren't generally able to be reactivated.
  9. Apr 21, 2012 #8
    A reaction has a particular activation energy in order to proceed. An enzyme acts as a catalyst, reducing the activation energy for the reaction to occur in the presence of the enzyme when compared to the reaction without the enzyme.

    If the enzyme is heated to a high temperature such that its conformation changes too dramatically and its binding sites and affinities change too much, it will no longer be able to work as an enzyme. When this occurs, the enzyme usually changes conformation such that even when it is cooled back down, it will remain "misfolded" -- that is to say, it will be unable to catalyze the reaction. Such an enzyme is said to be "denatured." This is a consequence of thermodynamics.

    Now, instead, suppose an enzyme is cooled. If the enzyme is cooled too dramatically along with the surrounding reagents, the average collision frequency will be reduced, and the probability of an effective reaction will decrease. The enzyme will also have less thermal energy and may change its conformation to a more energetically stable state. This would correspond to moving toward a local minimum on a potential energy curve as a function of the free varying parameters of folding. The enzyme would then be said to be in an "inactive" state since it is no longer functioning effectively as a catalyst. When heated again, the enzyme will absorb the thermal energy and it will assume a higher energy conformation and normally return to an active state.
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