Digestion and Absorption

• What happens to the large molecules in food? (Starch, proteins)

  They are broken down into smaller molecules, which can then move across the cell membranes - they are easily absorbed from the gut and into the blood to then be transported around the body
• What are carbohydrates broken down into?

  Disaccharides and then monosaccharides
• What are fats broken down into?

  Fatty acids and then monoglycerides
• What are proteins broken down into?

  Amino acids
• What are digestive enzymes used for?

  To break down biological molecules in food - they are released from specialised cells to mix with food.
• What is amylase?

  Digestive enzyme which catalyses the breakdown of starch (carbohydrate).
• How does amylase work?

  Catalyses hydrolysis reactions that break the glycosidic bonds in starch to produce maltose (disaccharide)
• What is amylase produced by?

  The salivary glands and then amylase is released into the mouth.

  The pancreas, which then releases amylase into the small intestine
• What is starch?

  Mixture of two polysaccharides which are each made from long chains of alpha glucose molecules
• What are membrane bound disaccharidases?

  Enzymes that are attached to the cell membranes of epithelial cells lining the ileum
• What do membrane bound disaccharidases do?

  They help break down disaccharides into monosaccharides by catalysing the hydrolysis of glycosidic bonds
• What is the enzyme which breaks down sucrose into glucose and fructose?

  Sucrase
• What is the enzyme which breaks down maltose into two glucose molecules?

  Maltase
• What is the enzyme used to break down lactose into glucose and galactose?

  Lactase
• What do lipase enzymes do?

  Catalyse the breakdown of lipids into monoglycerides and fatty acids by the hydrolysis of ester bonds in lipids
• Where are lipases made?

  Pancreas - then they are secreted into the small intestine
• What are bile salts and where are they produced?

  They are produced by the liver and they emulsify lipids - they make the lipids into smaller droplets.
• Why are bile salts important in lipid digestion?

  Smaller lipid droplets have a bigger surface area, therefore the formation of smaller droplets increases the surface area of the lipid which the enzyme lipase can work on
• What happens once the lipid is broken down?

  The monoglycerides and fatty acids stick to the bile salt, therefore forming tiny structures (micelles)
• What do micelles do?

  They help the product of lipid digestion to be absorbed
• How do peptidases break down proteins?

  They catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids
• What are endopeptidases?

  They hydrolyse the peptide bonds within the protein (in the middle)
• What are some examples of endopeptidases?

  Trypsin & chymotrypsin - synthesised in the pancreas and secreted into the small intestine
• What is an exopeptidase?

  They hydrolyse the peptide bonds on the end of a protein molecule - they remove single amino acids from the protein
• What are dipeptidases?

  Exopeptidase which work specifically on dipeptides and they separate two amino acids that make up a dipeptide by hydrolysing the peptide bond between them.
• Where are dipeptidases located?

  Cell surface membrane of epithelial cells in the small intestine
• Where are the products of digestion absorbed?

  Across the ileum epithelium and into the bloodstream
• How are different monosaccharides absorbed?

  Glucose - absorbed by active transport with sodium ions via a co-transporter protein

  Galactose - absorbed using the same co-transporter protein as glucose

  Fructose - absorbed via facilitated diffusion through a different transporter protein
• What do micelles do to help absorption?

  They move monoglycerides and fatty acids towards the epithelium and they release them to be absorbed since micelles constantly break up and reform.
• What are the benefits of monoglycerides and fatty acids?

  They are lipid soluble so they can diffuse directly across the epithelial cell membrane
• How are amino acids absorbed?

  Via co-transport - sodium ions are actively transported out of the ileum epithelial cells and into the blood which then this creates a concentration gradient. The sodium ions diffuse from the lumen of the ileum and into the epithelial cells through sodium dependent transporter proteins, carrying the amino acid with them.