Reading Comprehension
Multiple Choice Quiz

Digestion is the breakdown of large particles of food into smaller, more soluble molecules that can be absorbed into the body.
Digestion happens inside the gut, and relies on enzymes.

Enzymes pass out into the gut, where they catalyse the breakdown of food molecules.

Different enzymes
Different enzymes catalyse different digestion reactions.
Enzymes and their reactions catalysed

Enzyme Reaction catalysed
amylase starch to sugars
protease proteins to amino acids
lipase fatty acids to glycerol

Different parts of the gut produce different enzymes. This is shown in the table below:
Where produced
salivary glands, small intestine, pancreas
pancreas, stomach, small intestine
pancreas, small intestine

Overall, this means that:
        Amylase catalyses the breakdown of starch into sugars in the mouth and small intestine.
        Proteases catalyse the breakdown of proteins into amino acids in the stomach and small intestine.
        Lipases catalyse the breakdown of fats and oils into fatty acids and glycerol in the small intestine.

Different enzymes work best at different pH values. The digestive enzymes are a good example of this.
The stomach
The stomach produces hydrochloric acid which helps to begin digestion. Tjhis acid kills many harmful microorganisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions - in other words, at a low pH.
The small intestine
After the stomach, food travels to the small intestine. There, the enzymes work best in alkaline conditions. But the food is acidic after being in the stomach. A substance called bile neutralises the acid to provide the alkaline conditions needed in the small intestine.

Naming enzymes
The names of the different types of enzymes usually end in the letters -ase. Three of the most common enzymes with their chemical actions are:
  • lipase - breaks down fats
  • protease - breaks down proteins
  • carbohydrase - breaks down carbohydrates
Uses of Enzymes in the home
Enzymes allow certain processes to be carried out at normal temperatures and pressures, thereby reducing the amount of energy and expensive equipment needed.
Below are some common enzyme uses you should be familiar with.
used, together with protease, in biological detergents to break down the substances in stains into smaller, water soluble substances
used to pre-digest proteins during the manufacture of baby foods
used to convert starch syrup, which is relatively cheap, into sugar syrup, which is more valuable - for example, as an ingredient in sports drinks
used to convert glucose syrup into fructose syrup. Fructose is sweeter than glucose, so it can be used in smaller amounts in slimming foods