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Enzyme, Catalysts and Reactions

Enzymes, or biological catalysts, are three-dimensional globular proteins. Enzymes are integral in biological systems, they function to speed up metabolic reactions by lowering the activation energy of the reaction. Activation energy is the minimum amount of energy that is required to initiate atoms or molecules to a condition in which they can undergo chemical transformation of physical transport1. Examples of enzymes are amylases, proteases, and lipases found in the human digestive system.

Due to the complex folding in proteins, enzymes have substrate specificity. Binding of substrates occur at the active site, and this process can be shown through the ‘Lock and Key’ model or the ‘Induced Fit’ model. Enzymes can use cofactors, helper molecules, in catalyzing reactions. Cofactors can be classified as tightly bound or loosely bound to the enzyme, and organic or inorganic.  

Factors that affect enzyme activity are enzyme concentration, substrate concentration, temperature, pH and inhibitors. Derivation from optimal temperature and pH conditions denature the enzyme – the quaternary, tertiary and secondary structure of the protein is modified. Denaturation causes the enzyme’s active site to lose substrate specificity, and overall enzyme function.  Inhibitors act to decrease enzyme activity by binding and effectively blocking the active site, and there are four main types: competitive, uncompetitive, non-competitive and mixed.

Enzyme catalysis can be defined by their Vmax and Km which are both important in the Michaelis-Menten formula of enzyme kinetics. Vmax is the maximal velocity of enzyme catalysis, or how fast the enzyme can degrade the substrate. Km is substrate concentration where half of the enzyme’s active site are occupied (½ Vmax), this is called the Michaelis Constant. 

 

References

1 Activation Energy. (n.d.). In Encyclopedia Britannica online. Retrieved from http://www.britannica.com/EBchecked/topic/4535/activation-energy

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