Revision notes for Biology AS Unit 1 – Carbohydrates hydrolysis

Maltose + Water            makes             2 alpha    glucose

 

Sucrose + Water            makes           alpha Glucose + Fructose

 

Lactose + Water           makes            Glucose + Galactose

 

Starch + Water             makes                 Maltose

 

 

LOCATION ENZYME WHAT ITS BREAKING DOWN
Salivary glands Amylase Starch
Stomach Pepsin Proteins
Pancreas Amylase

Trypsin

Chymotrypsin

Carboxypeptidase

Lipase

Starch

Protein

Protein

Protein

Lipids

Ileum/small intestine Maltase

Sucrase

Lactase

Peptidase

Maltose

Sucrose

Lactose

Protein

 

Carbohydrate digestion

Enzymes are specific so it usually takes more than one enzyme to completely break down a large molecule. Enzymes are produced in different parts of the digestive system. Each enzyme works fastest at a different pH.

Firstly, amylase is produced in the mouth and pancreas. Amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose. The maltose is hydrolysed by maltase into the monosaccharide a-glucose. Maltase is produced by the lining of the intestine.

The process in humans:

  • Food in mouth and chewed by teeth to break it into smaller pieces, increasing surface area.
  • Saliva contains salivary amylase which hydrolyses starch in the food to maltose. It also contains mineral salts to help maintain pH at neutral which is the optimum pH for salivary amylase.
  • Food swallowed and enters the stomach where conditions are acidic. The amylase is denatured by the acid which prevents further hydrolysis of the starch.
  • After some time, food is passed into the small intestine where it mixes with the secretion from the pancreas (pancreatic juice).
  • Pancreatic juice contains pancreatic amylase which continues the hydrolysis of starch into maltose. The pancreas and intestinal wall produce alkaline salts to maintain the pH at neutral which is optimum pH for the amylase to function.
  • Muscles in intestine wall push the food along the small intestine. Its epithelial lining produces maltase. The maltase hydrolyses the maltose from starch breakdown into a-glucose.
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