enzymes basics

enzymes

• Enzymes are soluble protein molecules that can speed up chemical reactions in cells. These reactions include respiration, photosynthesis and making new proteins. For this reason enzymes are sometimes called biological catalysts.
• Each enzyme will only speed up one reaction as the shape of the enzyme molecule needs to match the shape of the molecule it reacts with (the substrate molecule). The part of the enzyme molecule that matches the substrate is called the active site.

enzymes, temperatures and ph

• At low temperatures, enzyme reactions are slow. They speed up as the temperature rises until an optimum temperature is reached. After this point the reaction will slow down and eventually stop.
• Most enzymes work fastest in neutral conditions. Making the solution more acid or alkaline will slow the reaction down. At extremes of pH the reaction will stop altogether. Some enzymes, such as those used in digestion, are adapted to work faster in unusual pH conditions and may have an optimum pH of 2 (very acidic) if they act in the stomach.

enzymes and shape (higher tier)

• Enzyme molecules are protein molecules that are folded into very precise shapes. Changing the order of amino acids would cause it to fold into a different shape – and the substrate molecules would no longer fit into the active site.
• Each enzyme's active site is suitable for one specific type of substrate – just like a lock that has the right shape for only one specific key.
• Changing the shape of the active site of an enzyme will cause its reaction to slow down until the shape has changed so much that the substrate no longer fits. When this happens the reaction stops. At this point we say the enzyme is denatured and is permanently damaged.
• Denatured enzymes
• Enzymes can be denatured by high temperatures and extremes of pH. Both high temperatures and extremes of pH change the bonds between amino acids in the enzyme, so changing its shape.
• Enzymes work slowly at low temperatures too – but this is because the substrate molecules have less energy and move into the active site more slowly. This is not a permanent change.