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Proteins, Catalysts and enzymes

Proteins are made up of chains of amino acids, different arrangements make different proteins. They act as:

  • structural components such as muscles and tendons
  • hormones such as insulin
  • antibodies, which destroy pathogens
  • catalysts in the form of enzymes

Enzymes (large protein molecule) are biological catalysts. The amino acid chains are folded into certain shapes so the reactant (substrates) can fit into the active site on the enzyme. Enzymes are involved in building large molecules from smaller ones; changing on molecule into another and breaking down large molecules into smaller ones.

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Factors affecting enzyme action


Like other reactions, the rat of enzyme-controlled reactions increase with temperature increase, but only up to 40(degrees). After this point, the amino acid chains begin to unravel and the shape of the active site changes (it has been denatured). It can no longer act as a catalyst and the rate of reaction drops dramatically.


The shape of the active site comes from forces between the different parts of the protein molecule. A change in the pH affects these forces and changes the shape of the molecule so the active site is lost.

Different enzymes have different pH levels that they work the best at.

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Enzymes in digestion

Most enzymes work inside the cells, but digestive enzymes work outside them. The enzymes pass out of the cells in the gut and then come into contact with as much food as possible when the digestive juices and food are mixed.

Carbohydrases are the enzymes that break down carbohydrates. Starch is broken down into sugars in your mouth and small intestine by amylase which is made in your salivary glands, pancreas and small intestine.

Protease breaks down protein food like meat, fish and cheese into amino acids. Protease is produced by your stomach, pancreas and small intestine. The break down takes place in your stomach and small intestine.

Lipids are broken down into fatty acids and glycerol in your small intestine. The reaction is catalysed by lipase enzymes made in your pancreas and small intestine.

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Speeding up digestion

The proteases in your stomach work best in an acid pH so the stomach also produces a concentrated solution of hydrochloric acid which allows the enzymes to work effectively and it also kills any bacteria that is taken in with food. Finally, the stomach also produces a thick layer of mucus that coats the walls to protect them from being digested by the enzymes and the acid. Then, the enzymes made in the pancreas and small intestine work best in an alkaline environment. Bile is made in the liver and stored in the gall bladder untill needed when it is squirted onto the acidic food as it enters small itnestine from the stomach to neutralise the acid and make the semi-digested food alkaline.

It is important for enzymes in the digestive system to have a large surface area to work on which isn't a problem with carbohydrates and proteins however fats don't mix well with watery liquids in your gut and stay as large globules that make it difficult for lipase to work. Bile emulsifies the fats breaking it up into smaller droplets.

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Making use of enzymes

Biological detergents are used to remove stans. The contain proteases and lipases which work best at lower temperatures so are more economically and environmentally friendly.

Proteases are used to make baby foods as they 'predigest' some of the protein which babies aren't very good at which helps provide the baby with the amino acids it needs.

Carbohydrases are used to convert sugar in starch (glucose) syrup which is used in food production. Starch is made by plants and is very cheap so is a good source of sweetness for food manufacturers. Sometimes isomerase is used to convert the glucose syrup into fructose syrup - both contain the same energy but fructose is sweeter so less is needed.

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