Biology B2 Unit 4

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Enzyme structure - part 1

An enzyme is a biological catalyst, a substance that changes the rate of reaction without being used up

They control all body chemical reactions

Enzymes are involved in:

  • building larger molecules from smaller ones
  • breaking down large molecules into smaller ones
  • changing one molecule into another

Enzymes lower the activation energy needed for a reaction to take place

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Enzyme structure - part 2

Enzymes are large protein molecules made from long chains of amino acids coiled and folded together to give an enzyme with a special shape with a hole in it, an active site

How enzymes work:

  • the substrate (reactant) of the reaction fits into the active site of the enzyme
  • the reaction takes place rapidly and the products are released from the surface of the enzyme
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Factors affecting enzymes - temperature


  • the rate of enzyme-controlled reactions increases as temp increases
  • optimum temp 40ºC - after that, the enzymes denature (the long chains of amino acids uncoil)


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Factors affecting enzymes - pH


  •  A change in pH changes the shape of the active site disabling it from functioning
  • different enzymes have different pH levels which they work best at like pepsin works best at pH 2.5 whereas amylase works best at pH 8
  • (http://www.bbc.co.uk/schools/gcsebitesize/science/images/gcsechem_18part1.gif)
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Aerobic respiration

Glucose + Oxygen   →   Carbon dioxide + Water (+ Energy)

C6H12 + O2   →   6CO2 + 6H2O (+ Energy)

Most of the chemical reactions in the body take place in the mitochondria:

  • Mitochondria are tiny rod-shaped bodies (organelles) which are found in almost all plants and animal cells
  • they have a folded inner membrane which provides a larger surface area for the enzymes involved in aerobic respiration

Uses of respiration:

  • releases energy from the food we eat so the body can use it
  • basic functions of life - building up large molecules from smaller ones to make new cell material (synthesis reaction)
  • making muscles contract (movement)
  • maintaining a constant body temp.
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Enzymes in digestion - part 1

The food you eat is made up of large insoluble molecules which need to be broken down or digested to form smaller, soluble molecules

These can be absorbed by your body and used by your cells. This chemical breakdown is controlled by your digestive enzymes

Digesting carbohydrates:

  • Starch is broken down to glucose by carbohydrases like amylase
  • Starts in the mouth and also takes place in the small intestine
  • Amylase is made in the salivary gland, pancreas and small intestine
  • The glucose made is used by the cells in the body for respiration
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Enzymes in digestion - part 2

Digesting proteins:

  • Protein food (meat) is broken down to amino acids by proteases
  • done in the stomach and small intestine
  • Protease made in stomach, pancreas and small intestine
  • the amino acids produced can be built up into all the proteins you need and new enzymes

Digesting fats:

  • Lipids (fats and oils) are broken down into glycerol and fatty acids by lipases
  • lipases are made in the pancreas and small intestine
  • glycerol and fatty acids can be used as source of energy or to build cell membranes, make hormones and as fat stores
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Speeding up digestion - part 1

The enzymes of the stomach work best in acidic conditions whereas enzymes made in the pancreas and small intestine work best in alkaline conditions

To cope with the different pH levels your enzymes need, your body produces different chemicals

The glands in the stomach produce hydrochloric acid to allow your protease enzymes to work effectively

Food produced in the stomach is acidic and the enzymes in the small intestine work best in alkaline conditions. The liver produces bile which is squirted onto the food, neutralising it and then making it alkaline which is ideal for the enzymes in the small intestine

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Speeding up digestion - part 1

The larger the surface area of the food = the faster the enzymes work on the food

Carbohydrates and proteins are easy to increase the surface area but fats don't mix with the watery liquids in the gut. They stay as large globules. To solve this, bile emulsifies the fats, giving it a larger surface area

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Uses of enzymes

Some micro-organisms produce enzymes which pass out of cells and can be used in different ways:

  • biological detergents contain enzymes to remove all kinds of stains from clothes to give a cleaner wash a lower temps

Pure enzymes have many uses in industry:

  • Proteases - used in the manufacture of baby foods. They pre-digest some of the protein in the food, making it easier for them to get the amino acids they need
  • Carbohydrases - converts starch into sugar (glucose) syrup. Used in food
  • Isomerise - converts glucose syrup into fructose syrup. Glucose and fructose syrup have the same amount of energy but fructose is sweeter so less is used to sweeten food. Good for slimming food
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A very useful set of cards, which I personally will be using to revise for my mocks. Thank you!



A clearly written set of cards with useful basic information on enzyme action. It might be useful to state that not all enzymes have a temperature optimum of 40 degrees C.  Some bacteria have optima as high as 70 degrees C. Use these cards with a set of revision notes that show some clear diagrams of enzyme action and the digestive system.



Cameron Mcnally




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