Enzyme structure and function

Enzymes are catalysts. Enzymes are usually proteins and are built up by amino acids connected by peptide bonds, just as pearls on a necklace. By interactions between the side-chains of the amino acid residues, the necklace folds into a unique three-dimensional structure. The specific sequence of amino acids affects both the three-dimensional protein structure and the catalytic properties of the enzyme.

Enzymes lower the activation energy of a reaction - that is the required amount of energy needed for a reaction to occur. They do this by binding to a substrate and holding it in a way that allows the reaction to happen more efficiently. 

The part of the enzyme where the substrate binds is called the active site. Here, the enzyme changes shape slightly, fitting tightly with the substrate and forming the enzyme/substrate complex.

Factors affecting enzyme activity

Enzyme activity can be affected by a variety of factors, such as temperature, pH, concentration and more. Enzymes work best within specific temperature and pH ranges, but it will vary a lot dependent on each enzyme and what organism that the enzymes derive from. Any sub-optimal conditions can cause an enzyme to reduce its ability to bind to a substrate which affects the activity of the enzyme.

  • Temperature: Increasing temperature generally speeds up a reaction, and lowering temperature slows down a reaction. However, extreme high temperatures can cause an enzyme to lose its shape (denature).
  • pH: Each enzyme has an optimum pH range where the activity will be at its highest. Changing the pH outside of this range will slow enzyme activity and in very extreme pH values it can lose its shape (denature).
  • Enzyme concentration: Increasing enzyme concentration will speed up the reaction, as long as there is substrate available to bind to. Once all the substrate is bound, the reaction will no longer speed up, since there will be nothing for additional enzymes to bind to.
  • Substrate concentration: Increasing substrate concentration also increases the rate of reaction to a certain point. Once all the enzymes have bound, any substrate increase will have no effect on the rate of reaction, as the available enzymes will be saturated and working at their maximum rate.

Common mistakes and misconceptions

  • "Enzymes are specific": The character of the enzyme active site gives each different type of enzyme its unique specificity to select substrates among many. However, the degree of specificity and selectivity is not always absolute. Some enzymes can act on a range of molecules, as long as they contain the type of bond or chemical group that the enzyme targets. Other enzymes are very specific towards their substrate and biotransformation. 
  • "Enzymes are consumed in the reaction": Enzymes are not reactants and are not used up during the reaction. Once an enzyme binds to a substrate and catalyses the reaction, the enzyme is released, unchanged, and can be used for another reaction. This means that for each reaction, there does not need to be a 1:1 ratio between enzyme and substrate molecules.
  • "Enzymes work best at 37 °C and neutral pH (human body)". Enzymes are found in a variety of organisms all over the world which includes organisms that exist in extremes of cold temperature such as the arctic, or very warm temperatures such as hot springs. These organisms produce enzymes which must be functional in the existing conditions. Enzymes which are found in very extreme conditions are sometimes called extremozymes as they are found in highly acidic/basic conditions (pH), high/low temperatures, high salinity, or other factors, that would otherwise denature typical enzymes.

Environmentally friendly catalysts

Generally, enzymes are considered as biodegradable, renewable and environmentally friendly catalysts. Therefore, the industry applies enzymes as active ingredients in various types of products (especially foods, diagnostics, detergents and personal care products) and in manufacturing processes (such as leather, paper, textiles, chemicals and pharmaceuticals). 

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