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Experiment 14. Dehydrogenase in yeast
During respiration, hydrogen atoms are removed from glucose molecules by enzymes called dehydrogenases and passed to various chemicals called hydrogen acceptors. As the hydrogen atoms pass from one hydrogen acceptor to another, energy is made available for chemical reactions in the cell. In this way, substances such as glucose provide energy for vital reactions in living organisms.
In this experiment, a dye called methylene blue acts as an artificial hydrogen acceptor. When this dye is reduced by accepting hydrogen atoms it goes colourless.
(a) Place about 30 mm of yeast suspension in a test-tube and, using a test-tube holder, heat this suspension over a small Bunsen flame until the liquid boils for about half a minute.
Then cool the tube under the tap.
(b) Label three test-tubes 1-3.
(c) Using a graduated pipette or syringe, place 2 cm3 of the boiled yeast suspension in tube 1.
(d) Using the graduated pipette or syringe, draw up 4 cm3 unboiled yeast suspension and place 2 cm3 in tube 2 and 2 cm3 in tube 3.
(e) Rinse the pipette or syringe and use it to place 2 cm3 distilled water in tubes 1 and 2.
(f) With the pipette or syringe, place 2 cm3 1 % glucose solution in tube 3.
(g) Prepare a water bath by mixing hot and cold water from the tap to obtain a temperature between 35 and 45 °C. Place all three tubes in this water bath. Rinse the pipette or syringe.
(h) Copy the table given below into your notebook.
(i) After 5 minutes draw up 6 cm3 methylene blue solution in the pipette or syringe and place
2 cm3 in each tube. Shake all three tubes thoroughly and return them to the water bath, noting the time as you do so. Do not shake the tubes again.
(j) Watch the tubes to see how long it takes for the blue colour to disappear, leaving the creamy colour of the yeast. A thin film of blue colour at the surface of the tube may be ignored but the tubes should not be moved. Record the times in your table.
(k) The experiment
During respiration, hydrogen atoms are removed from glucose molecules by enzymes called dehydrogenases and passed to various chemicals called hydrogen acceptors. As the hydrogen atoms pass from one hydrogen acceptor to another, energy is made available for chemical reactions in the cell. In this way, substances such as glucose provide energy for vital reactions in living organisms.
In this experiment, a dye called methylene blue acts as an artificial hydrogen acceptor. When this dye is reduced by accepting hydrogen atoms it goes colourless.
(a) Place about 30 mm of yeast suspension in a test-tube and, using a test-tube holder, heat this suspension over a small Bunsen flame until the liquid boils for about half a minute.
Then cool the tube under the tap.
(b) Label three test-tubes 1-3.
(c) Using a graduated pipette or syringe, place 2 cm3 of the boiled yeast suspension in tube 1.
(d) Using the graduated pipette or syringe, draw up 4 cm3 unboiled yeast suspension and place 2 cm3 in tube 2 and 2 cm3 in tube 3.
(e) Rinse the pipette or syringe and use it to place 2 cm3 distilled water in tubes 1 and 2.
(f) With the pipette or syringe, place 2 cm3 1 % glucose solution in tube 3.
(g) Prepare a water bath by mixing hot and cold water from the tap to obtain a temperature between 35 and 45 °C. Place all three tubes in this water bath. Rinse the pipette or syringe.
(h) Copy the table given below into your notebook.
(i) After 5 minutes draw up 6 cm3 methylene blue solution in the pipette or syringe and place
2 cm3 in each tube. Shake all three tubes thoroughly and return them to the water bath, noting the time as you do so. Do not shake the tubes again.
(j) Watch the tubes to see how long it takes for the blue colour to disappear, leaving the creamy colour of the yeast. A thin film of blue colour at the surface of the tube may be ignored but the tubes should not be moved. Record the times in your table.
(k) The experiment