July 18, 2021
- The digestive system breaks down large insoluble food molecules into smaller, soluble molecules
- This chemical breakdown of food depends on digestive enzymes
- Different types of digestive enzyme break down the three main types of food molecules: carbohydrates, proteins and fats, you will only have to know about these 3 in I/GCSE Biology
Digesting carbohydrates😅
- Food like break and potatoes are full of carbohydrates (substances made of carbon, hydrogen and oxygen)
- The simplest carbohydrates are called sugars and these can be built upinto more complex carbohydrates, such as starch
- Digestive enzymes that break down carbohydrates are known as carbohydrases
- Amylase is a carbohydrase that breaks starch down into sugars, which can then be absorbed by the small intestine or broken down into glucose by other carbohydrases
- An amylase is present in saliva
- Another amylase is made in the pancreas and released into the small intestine
Digesting proteins😁
- Proteases are enzymes that digest proteins, breaking them down into shorter chains and then into amino acids
- Pepsin is a protease made in the stomach. It works best in acidic conditions
- The stomach walls produce an acid, which makes the pH 2-3. This is the optimum pH for pepsin to break down portein as fast as possible
- However, the contents of the small intestine are alkaline and so the proteases released into the small intestine work best at about pH 8
Digesting fats🧐
- Lipases are enzymes that digest fats.
- Lipases chemically break down fat into fatty acids and glycerol
- Fat and water dont mix so the fats and oils you eat form globules in the watery digestive juices
- Large globules have a veyr small surface area to volume ratio, which means the lipases can only break down the fat molecules very slowly
- However, bile physically breaks down the large globules into tiny droplets, form as emulsion
- We say that bile emulsifies the fat
- The smaller droplets have a larger surface area, which makes it possible for lipase to break down the fat molecules far more rapidly
- More bile is released after a fatty meal
- Bile makes faeces brown
- The bile from the gall bladder is alkaline
- this helps neutralise the acid from the stomach and produces a slightly alkaline environment for the protease enzymes of the small intestine to work in
Reference: https://3dmss.bscs.org/static/45df82fd9164dd224e7f38c81f09c7b8/2f1b1/2_vil_3xpln1_webc2.jpg
Drafted by Catrina (Biology)