enzymes and digestion

• Ileum

  • a long muscular tube. Food is further digested in the ileum via enzymes produced by its walls and glands that pour their secretions into it. Inner walls are folded into a villi giving it a high surface area. Surface area is further increased by millions of tiny projections called microvilli on epithelial cells of each villus. Adapting the ileum for its purpose to absorb the products of digestion into the bloodstream.
• Large intestine

  • absorbs water, most water absorbed is water from secretions of many digestive glands
• Rectum

  • faeces stored before periodically removed by the anus in a process called egestion.
• Salivary glands

  • pass secretions via a duct in the mouth, contains amylase which hydrolyses starch into maltose
• Pancreas

  • large gland producing a secretion called pancreatic juice containing protease, lipase and amylase.
• Oesophagus -

  • carries food from mouth to the stomach
• Stomach

  • muscular sac with an inner layer that produces enzymes. ROLE: store and digest foods especially proteins, has glands producing enzymes which digest proteins.
• Physical digestion (step one of digestion)

   if food is large it is broken  down into smaller pieces by structures like teeth, making ingestion possible and also provides a large surface area for chemical digestion. Food is also churned up by muscles in the stomach walls also physically breaking it up.
• Chemical digestion

  • hydrolyses large insoluble molecules into smaller soluble ones, this is carried out by enzymes. All digestive enzymes function by hydrolysis.
• • It usually takes more than one enzyme to completely hydrolyze a large molecule. Typically one enzyme hydrolyses the molecule into small sections then other enzymes hydrolyse these sections into their monomers.
• Summary of carbohydrate digestion:

  • first the enzyme amylase is produced in the moth and the pancreas, amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose. Maltose is then hydrolysed into monosaccharides of alpha glucose by a second enzyme MALTASE produced in the lining of the ileum.
• Process of carbohydrate digestion up to stomach:

  1. Saliva enter the mouth via the salivary glands and mixes with food whilst chewing
  2. Saliva contains salivary amylase, this starts to hydrolyse any starch in food to maltose. Only has mineral salts to maintain pH to neutral as amylase works properly at this pH.
  3. Food is swallowed and enters the stomach where the conditions are acidic. This denatures the amylase preventing further hydrolysis of starch.
• Carbohydrate digestion from small intestine

  1. Food enters small intestine

  2. Mixing with pancreatic juice (secretion from pancreas)

  3. Pancreatic juice contains pancreatic amylase, continuing hydrolysis of remaining starch

  4. Alkaline salts produced by pancreas and intestinal walls to maintain neutral pH

  5. Muscles in intestine wall push food along ileum

  6. Epithelial lining produces disaccharide maltase

  7. Maltase hydrolyses maltose into monosaccharides, alpha glucose
• Sucrase = hydrolyses single glycosidic bonds in sucrose molecules . producing monosaccharides of fructose and glucose

  Lactase= hydrolyzes single glycosidic bonds in lactose molecules, hydrolysis produces monosaccharides of glucose and galactose.
• Lipid digestion

  • Lipids are hydrolysed by enzymes called lipase (produced in the pancreas) hydrolyze the ester bonds found in triglycerides to form monoglycerides and fatty acids.
  • Lipid first splits into tiny droplets called micelles by bile salts, produced in the liver. This process is emulsification and increases the surface area of lipids so action of lipase is speeded up.
• Protein digestion

  • Proteins are hydrolysed by a group of peptidases (proteases)
  • Endopeptidase -  hydrolyses peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules.
  • Exopeptidase = hydrolyse the peptide bonds on terminal amino acids of peptide molecules formed by endopeptidase release dipeptides and single amino acids.
  • Dipeptidase = hydrolyses peptide bonds between two amino acids of a dipeptide.