AQA AS Biology Unit 1: Carbohydrate Digestion

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Carbohydrate Digestion
Starch Digestion
Enzymes are specific; therefore it usually takes more than one enzyme to completely break
down a large molecule.
Typically one enzyme breaks down the molecule into smaller sections and then other
enzymes break down these sections further into their monomers.
These enzymes are usually produced in different parts of the digestive system.
This is because each enzyme works fastest at a different pH.
It is obviously important that enzymes are produced in the correct sequence.
Firstly, the enzyme amylase is produced in the mouth and the pancreas.
Amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the
disaccharide maltose.
The maltose is in turn hydrolysed into the monosaccharide a-glucose by a second enzyme,
Maltase is produced by the lining of the intestine.

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In humans the process takes place as follows:
Food is taken into the mouth and chewed by the teeth
This breaks it into smaller pieces, giving it a large surface area
Saliva enters the mouth from the salivary glands and is thoroughly mixed with the
food during chewing
Saliva contains salivary amylase
This starts hydrolysing any starch in the food to maltose
It also contains mineral salts that help to maintain the pH at around neutral
This is the optimum pH for salivary amylase to…read more

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Disaccharide Digestion
In addition to the digestion of maltose, there are two other common disaccharides in the
diet that need to be broken down.
Starch Digestion
In natural foods sucrose is usually contained within cells and there must be physically
broken down by the teeth in order to release it.
The sucrose passes through the stomach and into the small intestine, whose epithelial lining
produces the enzyme sucrase.…read more

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Lactose Intolerance
Lactose is a sugar found in milk and that is hydrolysed by the enzyme lactase.
Milk is the only food of young babies and so they produce relatively large amounts of
As milk forms a much smaller part of the diet in adults, the production of lactase naturally
diminishes during childhood.
However, in some people, this reduction is so great that they end up producing little or no
lactase.…read more


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