Enzymes

A CATALYST IS A SUBSTANCE WHICH INCREASES THE SPEED OF A REACTION, WITHOUT IT BEING CHANGED OR USED UP IN THE REACTION

Enzymes are large proteins and all proteins are made up of chains of amino acids.

Enzymes have special shapes so they can catalyse reactions:

• Every enzyme has an active site with a unique shape that fits onto the substance and they usually only catalyse one specific reaction.
• For the enzyme to work, the substrate has to fit into its active site. If the substrate doesn't match the enzyme's active site, then the reaction won't be catalysed.

Enzymes need the right temperature...

• Changing the temperature changes the rate of an enzyme-catalysed reaction.
• A higher temperature increases the rate, at first.
• But if it gets too hot, some of the bonds holding the enzyme together break and this changes the shape of the active site, so the substrate won't fit anymore. The enzyme has DENATURED.

...and they need the right pH:

• If the pH is too high or too low, it interferes with the bonds holding the enzyme together.
• This changes the shape of the active site and denatures the enzyme.
• All enzymes have an optimum pH (like it has an optimum temperature which is usually 37.5 degrees) and it is often neutral pH7, but not always.
  • For example: pepsin is an enzyme used to break down proteins in the stomach. It works best at pH2, which means it is well-suited to the acidic conditions there.
• Enzymes in the small intestine like a higher pH, whilst stomach enzymes work best at a low pH.

Carbohydrases convert carbohydrates into simple sugars...

• Amylase is an example of a carbohydrase and it is broken down into starch.
• Amylase is made in three places:
  • The salivary gland
  • The pancreas
  • The small intestine

Lipases convert lipids into glycerol and fatty acids...

• Lipids are fats and oils.
• Lipases are made in two places:
  • The pancreas 
  • The small intestine

Bile neutralises the stomach acid and emulsifies fats...

• Bile is produced in the liver and is stored in the gall bladder before it's released into the small intestine.
• The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline, so it neutralises the acid and makes conditions alkaline.
• It emulsifies fats (it breaks the fat into tiny droplets). This gives a much bigger surface area of fat for the enzyme lipase to work on- which makes digestion faster.

Proteases convert proteins into amino acids:

• Proteins are made in three places:
  • The stomach (pepsin)
  • The pancreas
  • The small intestine

The breakdown of food is catalysed by enzymes...

Salivary glands-These produce amylase enzyme in the saliva

Stomach:

• 1) It pummels the food with its muscular walls 
• 2) It produces the protease enzyme, pepsin
• 3) It produces hydrochloric acid for two reasons:
  • To kill bacteria
  • To give the right pH for the protease enzyme to work 

Liver- Where bile is produced. Bile neutralises stomach acids and emulsifies fats.

Gall bladder- Where bile is stored before it's relased into the small intestine.

Large intestine- Where excess water is absorbed from the food.

Rectum- Where the faeces are stored before it is released through the anus

Pancreas- Produces protease, amylase and lipase enzymes. It releases these into the small intestine.

Small intestine: 

• 1) It produces protease, amylase and lipase enzymes to complete digestion.
• 2) This is also where the digested food is absorbed out of the digestive system into the blood.