Enzymes+experiment

=INVESTIGATING THE EFFECT OF TEMPERATURE AND pH ON ENZYME ACTION=

1. Which tube shows that starch digestion has occurred? Give your reasons. Test tube B shows that starch digestion has occurred. When iodine is added to the mixture in test tube B to test for presence of starch, there was no observable change in colour. This means to say that no presence of starch was detected, and hence it could be deduced that the starch has been catalyzed by enzymes, whereby catabolic reactions cause starch to be broken down into glucose. Therefore, starch digestion has occurred. In test tube A, however, the mixture turns dark brown instead of yellowish-brown. One explanation we could offer for this observation was that the enzymes were less active at a lower temperature, hence the rate of reaction was slower, resulting in a more gradual change in colour of the mixture.
 * Part A**
 * Test Tube || Observations after adding iodine solution to mixture ||
 * A – 3cm3 of amylase solution placed in ice water reacting with 5cm3 of starch solution || Turns dark brown ||
 * B – 3cm3 of amylase solution placed in a water bath of 370c before reacting with 5cm3 of starch solution || No observable change in colour ||
 * C – 3cm3 of amylase solution placed in boiling water before reacting with 5cm3 of starch solution || Turns dark blue ||
 * D – 3cm3 of distilled water placed in water bath of 370c before reacting with 5cm3 of starch solution || Turns dark blue ||

2. Which of the test-tubes contained mixtures that gave a blue-black colour? Test tubes C and D contained mixtures that gave a blue-black colour.

3. Why did the mixtures in tubes stated in (2) remain blue-black? The mixture in test tube C remained blue-black because the enzymes were denatured when exposed to high temperature such as the boiling water. The enzymes' shapes are altered, resulting in them no longer being able to bind to their substrates. Hence, starch was unable to be catalyzed by enzymes, leading to a positive test for starch when iodine solution is added to the mixture. The mixture in test tube D remains blue-black because distilled water does not contain enzymes which can undergo catabolic reactions with the starch, hence the mixture remains blue-black.

4. What purpose does the tube D1 serve? Tube D1 serves as a control. A control is necessary in this particular experiment because results are only being recorded at the end of the experiment. Hence, its purpose is to allow us to compare the results.

5. Using your knowledge of the structure of starch, describe the test you would use to detect the presence of the substance produced as a result of the reaction in test tube stated in (1) above? Starch is composed of polymers of glucose. Long linear chains are called amylose. Amylose coils into a helical secondary structure resembling a tube with a hollow core. Certain molecules including fatty acids and iodine can lodge inside the core. The complex of iodine lodged inside the amylose tube produces a characteristic blue-black color.

6. What conclusion(s), based on the observations in this experiment, can be made about the effect of temperature on enzyme action? In conclusion, the rate of enzyme reaction increases as temperature increases. However, the enzyme molecules themselves also gain energy as the temperature rises so that they begin to vibrate; eventually, when the temperature is too high, the enzymes vibrate too much and become denatured - they lose their 3D shape and can no longer bind to their substrates. This results in a sharp drop in enzyme activity.

After – no observable change || After – turns yellowish-brown || After – no observable change || After – no observable change || 1. Which test tube shows that starch digestion has occurred? Give your reasons. Test Tube X shows that starch digestion has occurred. When iodine is added to the mixture in test tube X to test for presence of starch, there was no observable change in colour. This means to say that no presence of starch was detected, and hence it could be deduced that the starch has been catalyzed by enzymes, whereby catabolic reactions cause starch to be broken down into glucose. Therefore, starch digestion has occurred.
 * Part B**
 * Test tube || Contents || Iodine test ||
 * W || 2cm3 of starch solution + 2cm3 of HCL + 2cm3 of amylase || Before – turns dark blue
 * X || 2cm3 of starch solution + 2cm3 of distilled water + 2cm3 of amylase || Before – turns dark blue
 * Y || 2cm3 of starch solution + 2cm3 of NH4OH + 2cm3 of amylase || Before – turns dark blue
 * Z || 2cm3 of starch solution + 4cm3 of distilled water || Before – turns dark blue

2. Which of the test tubes contained mixtures that gave a blue-black colour? Test tubes W, Y and Z contained mixtures that gave a blue-black colour.

3. Why did the mixtures in tubes stated in (2) remain blue-black? The mixture in test tube W contained hydrochloric acid, a very strong acid with a very low pH. Hence, the enzymes might have been denatured by this extreme pH, resulting in it not being able to undergo catabolic reactions with the starch, so there was a positive test for starch was iodine solution is added to the mixture. In test tube Y, the mixture also turned blue-black. However, ammonium hydroxide is a relatively weak base, hence it should not have denatured the enzymes. The only plausible reason is that we might have made some errors during the experiment, such as adding a little too much NH4OH. In test tube Z, there was no presence of amylase, hence the starch was not catalyzed by any enzyme, resulting in the mixture turning dark blue when iodine solution is added.

4. What conclusion(s), based on the observations in this experiment, can be made about the effect of pH on enzyme action? In conclusion, extremes of pH may denature an enzyme, resulting in it not being able to undergo catabolic reactions with its substrate.

5. How does temperature and pH affect enzyme action? The rate of enzyme reaction increases as temperature increases. However, the enzyme molecules themselves also gain energy as the temperature rises so that they begin to vibrate; eventually, when the temperature is too high, the enzymes vibrate too much and become denatured - they lose their 3D shape and can no longer bind to their substrates. This results in a sharp drop in enzyme activity.

Extremes of pH may denature an enzyme, resulting in it not being able to undergo catabolic reactions with its substrate.

Part A involves recording the results only after the end of the experiment, but Part B involved recording results before and after the experiment. Hence, there would be a need for a control in Part A.
 * Differences between Part A and Part B

The good point about Part A is that it allows the substances to adapt to the conditions first (e.g. putting test tubes in various temperatures for 10 minutes) before mixing them together. This is so as to ensure that the mixtures are really exposed to the various conditions. This is unlike Part B, which mixes all the substances together and allow them to react. **