Enzymes

A catalyst is a substance which increases the speed of a reaction without being changed or used up in the reaction.

• Living things produce enzymes which act as biological catalysts. Enzymes reduce the need for high temperatures and we only have enzymes to speed up the useful chemical reactions in the body. 

• Enzymes are all proteins, and they work can work inside or outside of the cells, for example:
  • DNA replication - enzymes help copy a cells DNA before it divides by mitosis or meiosis.
  • Protein synthesis - enzymes hold amino acids in place and form bonds between them.
  • Digestion - various enzymes are secreted into the gut to digest different food molecules.

• Chemical reactions usually involve things either being split apart or joined together.

• The substrate is the molecule changed in the reaction.

• Every enzyme has an active site, and enzymes have a high specificity for thier substrate.

• This is because for the enzyme to work, the substrate has to fit into the active site. If the substrates shape doesnt match the active sites shape, then the reaction wont be catalysed. This is called the 'lock and key' mechanism, because the substrate fits into the enzyme just like a key fits into a lock.