Investigating a factor that affects the rate starch is digested by Amylase.

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Investigating a factor that affects the rate starch is digested by Amylase

Factors that affect the rate of digestion: 

  • Temperature affects the rate of digestion because most enzymes have a specific temperature that they work best at. This is usually body temperature for body enzymes.
  • pH affects the rate of digestion because most enzymes have a specific pH level at which they work best.

  • Concentration of substrate affects the rate of digestion because the more concentrated the substrate, the slower the rate of digestion will be for a constant amount of enzyme. This happens because there is too much substrate for the enzyme to digest quickly.
  • Concentration of enzyme affects the rate of digestion because the more concentrated the enzyme, the faster the rate of digestion will be for a constant amount of substrate. This happens because there are more enzymes available to digest the substrate.

Aim:

I am going to investigate how pH affects the rate that amylase digests starch.

Prediction:

I would expect that the rate of reaction between amylase and starch would be higher when it takes place at around pH 6. I think this because in the human mouth, the saliva is slightly acidic, pH 6. In the body, a delicate balance needs to be maintained between the optimal pH for each of it’s many enzyme reactions.

The pH an enzyme prefers depends on the enzyme itself. Enzymes work on substances called substrates. These react with the enzyme on part of the surface of the enzyme. This area is called the active site. There are two types of enzymes, breakers and builders. Breaker enzymes break up large molecules into smaller ones and builder enzymes join small molecules together to form larger ones. The diagram below shows how the two different types of enzymes work:

Amylase is a breaker enzyme because I am going to use it to digest starch. The active site of an enzyme can be changed by very acidic or very alkaline conditions. This happens because an acid has spare electrons called H+ ions, an alkali has spare electrons called OH- ions. It is these spare ions that attract or repel the enzymes. They can attach onto or break bits away from the enzyme’s active site and change its shape. This means that the substrates can no longer react with the enzyme because they don’t fit its active site. This will prevent a reaction taking place and is why I predict that the amylase will digest the starch at the fastest rate, when working at a pH of 6-7, around neutral.

Plan:

Preliminary Work:

Aim: to find out how fast Amylase breaks down starch

Method: we filled every well in a spotting tile with one drop of iodine solution. We then put 5ml of starch solution into a boiling tube. We also added 1ml of distilled water to the boiling tube and mixed the contents. Next we added 1ml of amylase into the boiling tube, starting the stop clock as we did so. Every 30 seconds, we removed a drop of the solution using a pipette and added it to the iodine in one of the wells in the spotting tile. We did this until the iodine stopped changing colour.

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Diagram:

Results: It took 5 minutes for the iodine to stop changing to a blue/black colour.

Evaluation: The change of the iodine’s colour to blue/black indicates that there is still starch present. After 5 minutes, when the iodine stopped changing colour, remaining brown/orange, we can tell that the amylase has digested all the starch, as there is no longer any starch present. The starch has been broken down into another substance by the amylase.

Because I am only investigating one factor, pH, I ...

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