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9.1: Role of enzymes

Microbiology for Earth Scientists · LibreTexts

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    From LibreTexts, under CC BY-SA 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    Enzymes help make life possible by speeding up (i.e., catalyzing) many biological reactions. They are usually composed of protein although some RNA-based enzymes are known to exist. Enzymes speed reactions by providing a reaction pathway with a lower activation energy \(\left(E_{A}\right)\), the energy barrier that exists between reactants and products in a chemical reaction (Fig. \(9.1\)).

    Diagram showing the energetic effects of enzymatic catalysis. Net Gibbs free energy of the reaction is the same with and without the enzyme, but the activation energy required for the reaction is lower with the enzyme present.
    Figure \(9.1\): Activation energy \(\left(E_{A}\right)\) of a biological reaction with and without enzymatic catalysis. \(\Delta G_{r}\) is the Gibbs free energy change of the reaction. Figure based on figure 14.1 of Garrett and Grisham (1999).
    https://commons.wikimedia.org/wiki/File:Enzymatic_reactions.png

    During an enzymatic reaction, reactant molecules bind with an enzyme to form a transitional state and ultimately reaction products. Molecules that can bind with an enzyme are referred to as substrates. The site on an enzyme where a substrate binds and catalysis can occur is known as the active site. The structure of an enzyme affects which molecules can bind to its active site, and thus determines which specific reaction the enzyme catalyzes. Figure \(9.2\) illustrates this aspect of enzymes based on an early conceptual model known as the lock and key model.

    Diagram illustrating the induced fit model of enzyme activity.
    Figure \(9.2\): Schematic illustration of the lock and key model. Substrates enter the active site, form a transitional complex, which can then form reaction products. Image source: public domain.
    https://commons.wikimedia.org/wiki/File:Induced_fit_diagram.svg

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