Why enzymes denature at high temperatures

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. This is one reason why tight homeostasis is physiologically necessary in many life forms. 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. This is because the enzyme can't work any faster even though there is plenty of substrate available.

So when the amount of available substrate exceeds the amount of enzymes, then no more substrate can be broken down. The enzyme concentration is the limiting factor slowing the reaction. As the concentration of the enzyme is increased, the enzyme activity also increases. This means that more substrate will be broken down if more enzyme is added. Again, this increase in enzyme activity does not occur forever.

So when the amount of available enzyme exceeds the amount of substrate then no more substrate can be broken down. The substrate concentration is the limiting factor slowing the reaction. Factors affecting enzyme action Physical factors affect enzyme activity. Temperature At low temperatures, the number of successful collisions between the enzyme and substrate is reduced because their molecular movement decreases.

How temperature affects enzyme action Higher temperatures disrupt the shape of the active site, which will reduce its activity, or prevent it from working.

A graph to show the effect of temperature on enzyme activity: The effect of pH Enzymes are also sensitive to pH.