• The purpose of digestion is to?break down large, insoluble molecules?into?smaller, soluble molecules that can be absorbed into the bloodstream
• Food is partially digested?mechanically?(by chewing, churning and emulsification) in order to break large pieces of food into smaller pieces of food which?increases the surface area for enzymes?to work on
• Digestion mainly takes place?chemically, where bonds holding the large molecules together are broken to make smaller and smaller molecules
• Chemical digestion is?controlled by enzymes?which are produced in different areas of the digestive system
• Enzymes are?biological catalysts?– they speed up chemical reactions without themselves being used up or changed in the reaction
• There are three main types of?digestive enzymes?–?carbohydrases, proteases and lipases

• Carbohydrases are enzymes that break down?carbohydrates?to simple sugars such as?glucose
  • Amylase?is a carbohydrase which is made in the salivary glands, the pancreas and the small intestine
  • Amylase?breaks down?starch?into?maltose
  • Maltase?then breaks down maltose into?glucose

   

Starch is broken down into glucose using two enzymes: amylase and maltase.

• Proteases are a group of enzymes that break down?proteins?into?amino acids
  • Pepsin?is an enzyme made in the?stomach?which breaks down proteins into smaller?polypeptide chains 
  • Proteases?made in the?pancreas?and?small intestine?break the peptides into?amino acids

   

Proteins are broken down using pepsin and other proteases

• Lipases are enzymes that break down?lipids?(fats) to?glycerol?and?fatty acids
  • Lipase enzymes are produced in the?pancreas?and secreted into the?small intestine

   

Diagram showing the digestion of lipids

轉載自savemyexams