B2 Chapter 3

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  • Created on: 22-12-15 10:33

Proteins, catalysts and enzymes 3.1

Protein molecules have different functions and can act as:

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

Catalyst- Speeds up a chemical reaction but is not used up in the reaction

Enzymes- Biological catalysts that control reactions in the body. Enzymes are large protein molecules made of amino acids with a specific shape. This allows other molecules (substrates) to fit into the enzyme protein. This is called the active site. Enzymes are involved in:

  • Building large molecules from lots of smaller ones
  • Changing one molecule into another
  • Breaking down large molecules into smaller ones

Enzymes work by the substrate (reactant) fitting into the active site like a lock and key. The reaction takes place rapidly and products are released from the surface of the enzyme. Enzymes can join small molecules together as well as break up large ones.

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Factors affecting enzyme action 3.2

Denatured- The enzyme has changed shape so can no longer speed up a reaction.

The rate of enzyme-controlled reactions increases as temperature increases until it gets up to about 40°C. After this the amino acid chains begin to unravel therefore the shape of the active sites change. Most human enzymes work best at 37°C.

A change in pH effects the enzyme action. The shape of the active site comes from forces between different parts of the protein molecule and a change in pH changes these forces. Therefore, it changes the shapes of the molecule and the active site is lost.

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Enzymes in digestion 3.3

Food is made up of large insoluble molecules that the body can't absorb so they are digested to form smaller, solube molecules which can be absorbed and used by your cells. This is controlled by digestive enzymes.

Digestive enzymes work outside your cells and are produced in glands (salivary glands, pancreas and lining of your gut). Enzymes then pass out of these cells into the gut itself. The gut is a hollow, muscular tube that squeezes your food. It breaks up food into smaller pieces and has a large surface area for the enzymes to work on. It uses digestive juices so enzymes come into contact with as much food as possible.

Carbohydrases- Enzymes that break down carbohydrates. They are broken down into sugars in your mouth and small intestines. It is catalysed by an enzyme called amylase.

Amylase- Enzyme produced in your salivary glands (also in your pancreas and small intestine).

Protease- Catalyst produced in stomach, pancreas and small intestine. It breaks down proteins.

Lipids (fats and oils) are broken into fatty acids and glycerol. It is catalysed by lipase (made in the pancreas then passed to small intestine).

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Speeding up digestion 3.4

Enzymes work best at different temperatures and pH so your body makes a variety of chemicals to keep conditions ideal for your enzymes throughout the gut.

Enzymes of the stomach work best in acid conditions so it produces hydrochloric acid.

The enzymes made in the pancreas and the small intestine work best in alkaline conditions. The acidic liquid from the stomach needs to become an alkaline mix in your small intestine. The liver makes an alkaline liquid called bile which is stored in the gall bladder till needed. Bile is squirted onto food as it comes into the small intestine from the stomach which neutralises the acid and provides ideal condtions for the enzymes.

You need the largest possible surface area of food for enzymes to work on. Fats stay as large globules (like oil in water) which makes it hard for lipase enzymes to act. Bile emuslifies the fats which means it breaks up large drops of fat into smaller ones.

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Making use of enzymes 3.5

Biological detergents- These contain proteases and lipases which break down the proteins and fats in stains. They work better at lower temperatures so it is also uses less electricity.

Uses for enzymes in the industry:

  • Proteases are used to make baby food as they predigest some of the protein in the food. It makes it easier for the baby's digestive system to cope with so they can get the amino acids they need from the food.
  • Carbohydrases convert starch into sugar syrup. It provides a cheap source of sweetness.
  • The sugar syrup can also be passed through the enzyme isomerase to change it into fructose syrup. Fructose contains the same amount of energy but is sweeter than glucose.


  • They catalyse reactions quickly and at low temperatures.


  • Denature at high temperatures and the pH needs to be controlled. They can also be expensive.
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High-tech enzymes 3.6

Enzymes in detergents- Biological detergents contain enzymes which break down biological stains. They work best at low temperatures so use less electricity. They did cause problems with allergies and although this has been fixed they were given bad publicity.

Enzymes and medicine:

  • Diagnose diease- If your liver is damaged or diseased, your liver enzymes might leak into your blood stream so your blood can be tested for these.
  • Diagnose and control disease- People with diabetes have too much glucose so get it in their urine. They can test for this using a strip that changes colour if it is present.
  • Cure disease- If the pancreas is damaged it can't make enzymes so you can take extra enzymes (E.g. Lipase) to allow you to digest food. If you have a heart attack, streptokinase is injected into your blood which is an enzyme that dissolves clots in the arteries. An enzyme is also being used to treat a type of blood cancer in children as the cancer cells cannot make one particular amino acid.
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