Why do enzymes denature at high temperatures

The enzyme, including its active site, will change shape and the substrate no longer fit. The rate of reaction will be affected, or the reaction will stop. A graph to show the effect of temperature on enzyme activity:. Enzymes are also sensitive to pH. Changing the pH of its surroundings will also change the shape of the active site of an enzyme. Many amino acids in an enzyme molecule carry a charge. Within the enzyme molecule, positively and negatively charged amino acids will attract.

This contributes to the folding of the enzyme molecule, its shape, and the shape of the active site. Changing the pH will affect the charges on the amino acid molecules. Amino acids that attracted each other may no longer be. Again, the shape of the enzyme, along with its active site, will change. Extremes of pH also denature enzymes.

The changes are usually, though not always, permanent. Enzymes work inside and outside cells, for instance in the digestive system where cell pH is kept at 7. Cellular enzymes will work best within this pH range. Different parts of the digestive system produce different enzymes.

These have different optimum pHs. The optimum pH in the stomach is produced by the secretion of hydrochloric acid. The optimum pH in the duodenum is produced by the secretion of sodium hydrogencarbonate. The following table gives examples of how some of the enzymes in the digestive system have different optimum pHs:.

A graph to show the effect of pH on an enzyme's activity:. Suggest an enzyme that would produce a trend as shown in the graph above. Pancreatic protease trypsin. Enzymes will work best if there is plenty of substrate available. As the concentration of the substrate increases, so does the enzyme activity. This means that more substrate can be broken down by the enzymes if there is more substrate available. This does not mean that the enzyme activity does not increase without end.

Like all proteins, enzymes are linear chains of amino acids that fold to produce a three-dimensional structure. The sequence of the amino acids specifies the structure which in turn determines the catalytic activity of the enzyme. Although structure determines function, a novel enzyme's activity cannot yet be predicted from its structure alone.

Enzyme structures unfold denature when heated or exposed to chemical denaturants and this disruption to the structure typically causes a loss of activity. Protein folding is key to whether a globular protein or a membrane protein can do its job correctly.

It must be folded into the right shape to function. But hydrogen bonds, which play a big part in folding, are rather weak, and it does not take much heat, acidity, or other stress to break some and form others, denaturing the protein.