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Skip to 0 minutes and 10 secondsThis practical is an engaging class practical which illustrates the use of immobilised enzymes, in the form of alginate beads, to catalyse the breakdown of lactose in milk into glucose and galactose. Many humans are lactose intolerant and commercially produced lactose free milk is available. Surprisingly, cats are also lactose intolerant. The context of producing milk for cats makes this interesting for students. Sodium alginate reacts with calcium chloride to make the gel we are using to immobilise the enzyme. This can be quite difficult to dissolve. It needs warm water and lots of stirring. It is important that all of the solutions are made up using distilled water.

Skip to 0 minutes and 59 secondsMix 2ml of lactase with 8ml of sodium alginate.

Skip to 1 minute and 15 secondsTo ensure even sized immobilised enzyme beads, cut the end of a 1ml plastic pipette and attach it to the end of the syringe. This will control the volume of mixture dripping into the calcium chloride. Drop the mixture through the syringe into the calcium chloride solution. This will form the beads.

Skip to 1 minute and 41 secondsWhen all of the enzyme mixture has passed through pour the beads into a tea strainer and rinse with distilled water.

Skip to 1 minute and 52 secondsNow we will use the immobilised enzyme to catalyse the breakdown of lactose into glucose and galactose. First, we will test for the presence of glucose in the milk with an easy semi-quantitative method.

Skip to 2 minutes and 15 secondsAs the strip shows, there isn’t any glucose present. Connect a short piece of tubing to the end of the syringe. Clip it shut with a Hoffman clip.

Skip to 2 minutes and 29 secondsPour the enzyme beads into the syringe.

Skip to 2 minutes and 39 secondsPour the milk into the syringe and leave for 10 minutes.

Skip to 2 minutes and 47 secondsLet the milk run out of the syringe and test it for glucose using a fresh test strip.

Skip to 2 minutes and 58 secondsWhen the strip changes colour this indicates the presence of glucose. A different colour indicates different quantities of glucose.

Immobilised enzymes

This is our second of three videos as part of the learning intentions activity.

Students will love this very simple technique for immobilising enzymes in alginate beads. The protocol for this practical is linked below.

You can use exactly the same technique to immobilise algae to look at the rate of photosynthesis with quantifiable and replicable results. Put the algae/alginate beads in hydrogen carbonate indicator solution (also called bicarbonate indicator) and watch the colour change as carbon dioxide is produced. This can be used to investigate the rate of photosynthesis under different environmental conditions.

Take a look at the STEM Resource for this alternative practical.

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This video is from the free online course:

Teaching Practical Science: Biology

National STEM Learning Centre

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