Enzymes

• Large food molecules are digested by enzymes into smaller molecules. These products of digestion are then absorbed into the bloodstream.
• Enzymes catalyse (speed up) chemical reactions.
• Enzymes are large protein molecules and they have a groove on their surface called the active site. The active site is where the substrate attaches to.

  
• The substate fits perfectly into the active site.

  
• The enzymes now breaks down the substrate into the products.

  
• However, this it not always the case. As enzymes are specific. The substrate must fit perfectly into the active site. (the lock and key theory)
• Proteins are broken down by enzymes called proteases. We find these in the stomach, the pancreatic fluid, and the small intestine.

  
• Proteins are long chains of chemicals called amino acids. When we digest proteins, the protease enzymes convert the protein back to the individual amino acids. Which are then absorbed into the bloodstream. When the amino acids are absorbed by the body cells, they are joined together in a different order to make human proteins.
• Like this...

  
• Starch (which is a carbohydrate) consists of a chain of glucose molecules. Carbohydrates are broken down by enzymes called carbohydrases. In the case of starch this is called amylase.
• When carbohydrates like starch are digested, we produce simple sugars. Amylase is found in the saliva and pancreatic fluid. Like this...

  
• A lipid molecule, consists of a molecule of glycerol attached to three molecules of fatty acids. Like this...

  
• Lipid molecules are digested by the enzyme lipase. This produces glycerol and fatty acids. We find lipase in the pancreatic fluid and also in the small intestine. Like this...

  
• Enzymes act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up in the reaction.

  • Enzymes reduce the need for high temperatures.
  • They are biological as they are made in cells.
• Enzymes are necessary to all living organisms as they allow all metabolic reactions to occur at a rate that can sustain life.

  • Different biological reactions all have a specific enzyme to help control the reaction.
  • Enzymes are made of protein and have a unique shape to help them function.
• The active site

  • Chemical reactions usually involve changing a particular molecule.
  • which can be split apart or joined to another molecule.
  • The molecule being changed is known as the substrate.
  • Each enzyme has a specially shaped region known as an active site.
  • The active site allows the enzyme to bind to the substrate.
  • Once bound to the active site, the chemical reaction takes place.
• The lock and key theory diagram.

  
• The enzyme is like a lock and the substrate is the key that fits into the active site (like a keyhole).

  • For an enzyme to work the substrate has to fit in the active site.
  • If the substrate is not the correct shape it will not fit into the active site.
  • Then the reaction will not be catalysed.