6.9 - Enzymes and digestion Flashcards
What is the function of the salivary gland
- Produces amylase
- produces saliva to lubricate food to make it easier to swallow
What is the function of the oesophagus
- muscular tube (smooth muscle)
- moves food to stomach by peristalsis movement
What is the function of the stomach
- Hydrochloric acid hydrolyses bacteria in food
- produces protease enzyme (pepsin)
—>it’s the beginning of protein digestion
What is the function of the pancreas
- secretion of digestive enzymes; amylase, lipase and protease
- secretion of neutraliser (sodium hydrogen carbonate)
What is the function of the liver
- produces bile
- stores glycogen, iron and vitamins A,D,E,K
- removes toxins/urea
What is the function of the gall bladder
- stores bile which emulsifies lipids to increase SA for lipase action
What is the function of the small intestine
- Absorption of soluble food
- also produce some enzymes: lipase, protease and carbohydrase
What is the function of the large intestine
- Absorption of water
- storage of faeces
What enzyme is used to break down starch and what is the product(s)
- amylase
- maltose
What enzyme is used to break down maltose and what is the product(s)
- Maltase
- glucose
What enzyme is used to break down sucrose and what is the product(s)
- sucrase
- glucose + fructose
What enzyme is used to break down lactose and what is the product(s)
- lactase
- glucose + galactose
What enzyme is used to break down triglycerides and what is the product(s)
- lipase
- 3 fatty acids + 1 glycerol
What enzyme is used to break down protein and what is the product(s)
- 3 enzymes
1: endopeptidase (acts on the middle) —produces —> peptides
2: exopeptidase (acts on the ends) —produces —> peptides
3: Dipeptidases —produces —> amino acids
Define ingestion
Putting food into the alimentary canal / digestive system
Define digestion
Hydrolysis of large insoluble food molecules into small soluble ones
Define absorption
The uptake of soluble food molecules into body cells
Define assimilation
Incorporation and use of soluble food molecules in cells and tissues
Define egestion
Removal of undigested food from the body
What are the different stages of digestion
- Physical digestion
- Chemical digestion
What is physical digestion
- Large food = broken down into smaller molecules (done by the teeth)
- it makes it possible to ingest food and provides a larger SA for chemical digestion
- food is churned by muscles in the stomach wall to further break it down
What is Chemical digestion
- hydrolyses large insoluble molecules into smaller soluble ones
- carried out by enzymes which function by hydrolysis (adding water to split up the chemical bonds holding the molecule together)
- enzymes are specific, so we need a whole range of them:
1. Carbohydrates (hydrolyses carbohydrates into monosaccharides)
2. Lipases (hydrolyse lipids into glycerol and fatty acids)
3. Proteases (hydrolyse proteins into amino acids)
Describe the process of carbohydrate digestion
- saliva enters the mouth from the salivary glands and is mixed with food when chewing
- saliva contains amylase which hydrolyses the alternate glycosidic bonds of any starch molecule into maltose. It also contains mineral salts that help to maintain the pH at neutral (optimum pH)
- swallowed food enters the stomach where conditions are acidic (denatures amylase, preventing further hydrolysis of starch)
- food then moves into the small intestine, where it’s mixed with secretions of enzymes from the pancreas
- this secretion contains pancreatic amylase which continues hydrolysis of any remaining starch to maltose. Alkaline salts are produced by both pancreas and intestine wall = maintains the pH at around neutral so that amylase can function
- Muscles in intestine wall push food along the ileum. Ileum epithelial lining produces maltase which is released into the lumen of the ileum, attached to the CSM of the epithelial cells that line the lumen (referred to membrane-bound disaccharidase)
- maltase hydrolyses the maltose from starch breakdown into alpha glucose
As well as maltase, what other disaccharidases are produced
- sucrase
—> hydrolyses the single glycosidic bond in the sucrose molecule. This hydrolyses produces the 2 monosaccharides glucose and fructose - lactase
—> hydrolyses the single glycosidic bond in the lactose molecule. This hydrolysis produces the 2 monosaccharides glucose and galactose
Describe the process of lipid digestion
- bile (produced by liver) is released into the small intestine, where it emulsifies lipids and neutralises stomach acid
- lipases are made in the pancreas and work in the ileum
- bile salts (produced by liver) emulsifies the lipids (larger SA, better for lipases to work on them)
- once lipids are broken down into the fatty acids and monoglycerides, they stick to bile salts to form micelles
- the micelles help to transport the fatty acids and monoglycerides to the epithelial cells which moves by diffusion
- the micelles constantly break up and reform so they can release fatty acids and monoglycerides allowing them to be absorbed
- it’s important to remember that whole micelles aren’t taken up across the epithelium
- monoglycerides and fatty acids are lipid-soluble, so can diffuse across the epithelial cell membrane without the need for a transporter
What are the 2 advantages of lipid digestion
- lipid droplets increases the SA for enzyme action for faster hydrolysis of lipids
- Micelle formation carry fatty acids and glycerol to the cell
Describe the process of protein digestion
- proteins are large + complex = so they need to be hydrolysed by a group of different enzymes called peptidases (proteases). There are 3 types:
1) Endopeptidases: hydrolyses the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
2) Exopeptidases: hydrolyse the peptide binds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way they progressively release dipeptides and single amino acids
3) Dipeptidases: hydrolyse the bond between the 2 amino acids of a dipeptide. Dipeptides are membrane-bound, being part of the CSM of the epithelial cells lining the epithelium
