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Enzymes and activation energy.

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Enzymes and activation energy.

Postby NewtoBiology » Wed Jul 08, 2009 2:09 am

Hello Biologists,

Q: Enzymes greatly decrease the activation energy. Explain two of the way they do this and be specific in terms of chemical mechanisms.

A: I have read my chapter 2 times, and have come up with the following answer. I must admit, I am stumped on the 'terms of chemical mechanisms' part of the Question. Would you please be so kind to read my answer and tell me if I am correct or totally in the wrong baseball field. Furthermore, if it is totally off, could you please give me a clue as to help me get back on track. THANK YOU for your time!!


Enzymes greatly decrease the activation energy in 2 distinct ways:
i. Lowering required energy: An enzyme’s selective three dimensional shape, brings the reactants (or substrates) closer together into its active site, therefore allowing the chemical bonds to weaken and change with less energy. An enzyme therefore lowers the entropy of substrate, freeing them from translational and rotational movements.
ii. Increasing reaction time: An enzyme acts as a biological catalyst, increasing the rate of the reaction without being changed into a different molecule, and without raising the temperature. However, an enzyme does not add energy to a reaction but rather it speeds up a reaction by altering the electrostatic character of the substrate molecule, by utilizing its charged or non polar side chains. This in turn increases the rate of reactivity of the substrate and stabilizes the transition state.

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Postby MrMistery » Wed Jul 08, 2009 3:20 am

i think chemical mechanisms means talk about acid-base catalysis and the like
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Re: Enzymes and activation energy.

Postby jonmoulton » Wed Jul 08, 2009 3:25 pm

Two comments:
1. The second section should be titled "decreasing reaction time". An increased rate means a decreased time.

2. In your first section, you comment on the three dimensional shape of the enzyme (I assume you specifically mean its active site). It is more than just shape that is of concern here, it is the electrostatic topology of the active site. Areas of higher or lower electron density relative to the nuclear charge in that region lead to binding or repulsion of substrate molecule(s) and make groups more or less reactive. Changing local electron density directly affects reaction mechanisms, which are for the most part driven by electronic interactions (though other factors, such as kinetic energy and entropy change, also play a role). Take a look at the "Visualizing surface potentials" image in: http://cardon.wustl.edu/MediaWiki/index.php/How_do_I_visualize_the_electrostatic_potential_around_my_biomolecule%3F
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Re: Enzymes and activation energy.

Postby kolean » Wed Jul 08, 2009 5:04 pm

From Wikipedia on Enzymes:

The mechanism of enzyme catalysis is similar in principle to other types of chemical catalysis. By providing an alternative reaction route and by stabilizing intermediates the enzyme reduces the energy required to reach the highest energy transition state of the reaction. The reduction of activation energy (ΔG) increases the number of reactant molecules with enough energy to reach the activation energy and form the product.

So I really think you answered the question in your first paragraph.
NewtoBiology wrote:An enzyme’s selective three dimensional shape, brings the reactants (or substrates) closer together into its active site,

This is the alternative route, and:
NewtoBiology wrote:allowing the chemical bonds to weaken and change with less energy

This is the stabilizing intermediates, or transition states.

All of your other answers support this as affects from the chemical catalysis.
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Postby prokaryotics » Sat Jul 11, 2009 9:09 am

Enzymes attach to a substrate and weaken intermolecular forces within the substrate and thus weaken their bonds so the reaction takes place much quicker.
As you see otherwise it would take a greater amount of time for a reaction to occur as a reaction requires the breaking of bonds (sometimes covalent) within a compound.

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Re: Enzymes and activation energy.

Postby misunderstandingbio » Sun Sep 15, 2013 3:37 pm

QUESTION: Explain how enzymes lower activation energy
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