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Speeding up reactions: biological vs. chemical catalysts

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Most chemical reactions go pretty slowly at room temperature. This is good news most of the time, otherwise random parts of the environment would be exploding at regular intervals, but bad news for industrial processes which need reactions to occur. In order to speed them up, catalysts are used. A catalyst is any substance that speeds up a reaction without taking part in it so at the end of the reaction you have the same amount of catalyst as you started with.

A pathway for the process of catalysis. X and Y are reactants (input) while Z is the final product. C is the catalyst.

Industrial catalysts are often metals, as most metals have a large number of electrons which are a little cavalier about exactly how close to the central atom they need to be. This allows the metals to use these electrons to help out in reactions before claiming them back once the reaction is over. Examples are iron-based catalysts used for making ammonia (the Haber-Bosch process) and the nickel catalysts used for making saturated fats.

Biological catalysts work on a very different principle. Rather than being metals with fast-and-loose electrons, biological catalysts are large complex molecules called enzymes, which contain specific pockets for the reactants to fit into. Once they are trapped inside the enzyme aids the reaction, either by forming temporary bonds with the reactants to help them fit together, or by simply holding them close enough to each other to actually react and form the product.

A simplified diagram for the mechanism of enzyme catalysis. In reality there's a lot more interactions, bonding, and exciting biochemistry involved, but this is a good approximation of the overall process. Image creative commons via wikimedia, credit link below.

Most enzymes are found inside organic lifeforms, which means that they do not need high temperatures to function while metal catalysts tend to need a bit of an energy kick to get going. In fact enzymes will denature, or break, if heated up too far beyond their optimum temperature (for most around 40 degrees, although some bacterial enzymes can work at 100 degrees). In some cases, such as in biological washing powders, this can be a huge benefit as it means less energy is needed for the reaction and the clothes can be washed at lower temperatures. In some industrial processes, however, high temperatures are needed to increase the rate of reaction so cooling everything down to 40 degrees is impractical.

Another important point about enzymes is that unlike the metal catalysts they are incredibly specific. As the reactants fit into pockets inside the enzyme each enzyme can only fit the molecules it’s meant to be catalysing. And as enzymes are large and complex molecules it’s not so simple to just design them to fit the reactants you need. Again, this is fine for biological washing powders, as there are plenty of enzymes that have evolved to break down egg stains, blood stains, and form strange little bobbles on jumpers. For chemical processes it can be a bit more difficult – not many organisms have evolved to remove the toxic gases from petrol, or synthesise sulfur dioxide.

There is some work being done designing enzymes for specific purposes, to hopefully increase the number of reactions that can be catalysed by biological means. It’s not the easiest job in the world though, as enzymes are made up of massive protein chains folded in strange and interesting ways and tweaking one part of them can have unforeseen repercussions on the whole molecule. It’s an exciting area of research though, with implications for industrial and medical research as well as the academic.

Credit link for image 2.

Other posts in the Chemistry series: Watervan der Waals forcesIonic bondsMetallic bondsCarbonAcids and pH

S.E. Gould About the Author: A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs. Follow on Twitter @labratting.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Uncle.Al 4:40 pm 01/12/2014

    Most chemical reactions go pretty slowly at room temperature” Thermodynamics proposes, kinetics disposes. Don’t mistake a kinetic barrier for slow kinetics thereafter. “Industrial catalysts are often metals” What part of the Periodic Table lower 92 isn’t metals? One trelide, two tetralides, two pnictides, two chalcogenides, the halogens – 11/92 elements other than the inert gases.

    Biological catalysts work on a very different principle.” Like cyanide vs. thiamine catalyzing the benzoin condensation? If biochemistry really knew stuff about catalysis, it would gene-gineer RuBisCO – the slowest, least efficient enzyme on Earth. RuBisCO is the carbon fixation bottleneck in photosynthesis. RuBisCO is the reason growing fuel is madness. We could end hunger forever with a year in the lab, but it would be wrong.

    unlike the metal catalysts they are incredibly specific.” Lipases as a class will swallow most anything short of sucrose polyester. “Most enzymes are found inside organic lifeforms” as opposed to what, rock? (But wait! The horta!)

    Site-directed mutagenesis can spin pretty much anything enzymatic, then to be banned for having “unknown hazards.” We live in a Golden Age, complaining about all the yellow.

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  2. 2. S.E. Gould in reply to S.E. Gould 5:30 pm 01/12/2014

    Thanks for your comment! I think the response to most of your issues is that I try to write my posts, especially the chemistry ones, for a wide audience, rather than just the scientifically educated. Hence the lack of thermodynamic discussion, the extra clarification of what enzymes are and my use of ‘metals’ to mean ‘transition metals’ (as although potassium is a metal very few people generally think of it as such).

    Rubisco is indeed an ‘inefficient’ enzyme but only from the point of view of someone wishing to make photosynthesis happen as rapidly as possible. From the point of view of a plant, which is simply aiming to survive and propagate, Rubisco has evolved to a specific enzymatic niche. There is certainly a large amount of current research being done on it, as its such a fascinating molecule.

    As a final word, I’m pretty sure that world hunger is no longer caused by a physical lack of food. Your respect for the abilities of plant science is admirable but even if a more efficient Rubisco could be designed and constructed within a year, and even if plants could photosynthesise and grow with such a molecule, I doubt poverty and hunger would he eradicated. There are queues for food banks in the UK at the moment, and its not the fault of Rubisco.

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  3. 3. Uncle.Al 7:54 pm 01/12/2014

    Eradicate hunger, homelessness, poverty; the lame, halt, dim-witted, and proven unable; by outlawing mandated charity. Anyone may voluntarily give of his own wallet, but nobody can give by fiat from another’s. Mediocrity is a vice of the doomed. March or die.

    Government solves the paradox of want amidst plenty by destroying the plenty. An advocate makes virtue of failure. The worse the cure the better the treatment – and the more that is required. Elitism insists the better is preferable to the worse. I am an elitist.

    Science can do near anything given budget, freedom to pursue, and personal reward for success. That is exactly the way a managed enterprise does not operate. Rather than foster brilliance we allocate for its suppression. Night is dark so you can imagine your fears without distraction.

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  4. 4. S.E. Gould in reply to S.E. Gould 5:29 am 01/13/2014

    No, taxes do not cause hunger either. You insist the better is preferable to the worse, yet your definition of “better” is that huge numbers of people should he left to suffer so that you can feel more brilliant without them.

    I don’t know what kind of world you live in, but we are not exactly living in an age with a shortage of scientific advancement. Over the last century huge leaps in medical, industrial and blue sky research have been made, and continue to be made, by scientists all over the world. People are living longer, experiencing more, travelling further. There are more scientists now and more scientific discovery than there has ever been.

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  5. 5. Uncle.Al 5:09 pm 01/13/2014

    huge numbers of people should he left to suffer” Not at all. Huge numbers of people should be left to die of their own hands and beliefs.
    How much more can you survive?

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  6. 6. S.E. Gould in reply to S.E. Gould 5:37 pm 01/13/2014

    I do not support leaving people to die and find the idea of doing so utterly repulsive, particularly coming from someone fortunate and comparatively well off. Any further comments that are not directly related to the content of this blog post will be deleted.

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  7. 7. Christotheb 2:01 pm 03/8/2014

    I would absolutely have loved to quote “most metals have a large number of electrons which are a little cavalier about exactly how close to the central atom they need to be.” in an essay I’m currently working on in Chemistry, but alas, my teacher said it was not to be.
    All being well, I’ll be studying Biochemistry next year, and your blog is a good read to keep me excited!

    Link to this
  8. 8. S.E. Gould in reply to S.E. Gould 4:53 am 03/13/2014

    Thanks for the comment! Good luck with your biochem studies, it’s a tough subject but really fascinating.

    Link to this

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