Notes on the kinetics experiment Fall 09 Read the write-up on how enzymes work o

Question

Notes on the kinetics experiment Fall 09 Read the write-up on how enzymes work on pages 15.21 from this handout Set up the apparatus shown on page 22. If we do not have the glass tubes needed for that set-up we can use the set ups shown on the figures on the next page It may be wise to do a trail run as outlined on page 23 to get used to the set-up before you collect your data indicated on this page. l)Use a 600 mL beaker as a water bath set at 37 c (use a hot plate to get this tempor try the hot water faucet to see ifthe water from it reaches 37 C. Note: 37C mirrors the temperature of living organisms so we want to carry out our experiments under biological temperature as well. However, depending on how potent the yeast is and how fresh the hydrogen peroxide is it may be necessary to raise the temperature to 50 C to increase the reaction rate to get reasonable results if our system is sluggish. If we go to 50 C for the reaction temperature you will not be able to get to this temperature with the hot water from the faucet and therefore mustuse the hot plate to warm the water bath to 50 2) Use a 125mL Erlenmeyer flask for the reaction vessel. Again if the glassware for the set-p o page 22 is not available we can use either the 125ml filtering flask (with the ide-arm) or a large test tube with a side arm as the reaction vessel in either case using a cork or rubber stopper to seal the test tube or flask Place the reaction vessel in the 37 c (500C) water bath. 3)Add 0.300 grams of dry yeast to the 100mL volumetric flask, then fill to the mark with distilled water, stopper the flask then gently invert the flask several times to mix the contents, then place the flask into a pan of ice and water to keep the solution cool. 4) Measure out 10ml of this solution (mixing the contents of the volumetric flask immediately before measuring out the 10mLs and place it into the reaction vessel. MAKESURE YOU CHECK THE TEMPERATURE OF THE 10mLsOF SOLUTION IN THE 125ml FLASK TOMAKE SURE THE TEMPERATUREHAS RISEN TO 37 cor 50°C before continuing with step 5 5) Stopper the gas delivery tube to the reaction vessel, then add the hooked end of the gas delivery tube to the water filled inverted graduated cylinder in the second 600mL beaker (see diagram in lab write-up ge 22) or for the modified system stopper the flask or test tube, then add the rubber hose attached to the side amm of the flask or test tube into the water-filled inverted graduated cylinder in the second 600ml beaker. 6) Lift the stopper from the 125mL flask, then add 4mL of hydrogen peroxide to the flask, re-stopper the flask, and swirl for about 30 seconds. Note any initial displacement of water in the graduated cylinder, and start timing the reaction for 3minutes Indicate the volume of water displaced only during the 3-minute period. Ex 1.00mL displaced during 30-second swirl, and a total volume of 9mL displaced after 3:00 minutes longer. The volume displaced during the 3:00 minute interval is 8mL. This process is repeated 8 times with the following variations: a) Use 4mL of 3% (0.88M) hydrogen peroxide.

Explanation / Answer

1. In the experiment, the temperature of the water bath is maintained at 37C. Human body temperature is 37C under normal conditions and therefore, the temperature of the bath is maintained at 37C so that the experimental temperature replicates the biological system.

However, the above temperature may not be effective in bringing about the desired reaction and therefore, to increase the efficiency of the reaction, the temperature of the water bath is raised to 50C by heating gradually on a hot plate.

2. Chemical reactions mainly differ in the mode of operation in animate and inanimate objects. The rate of the reaction in animate and inanimate objects is different.

Reactions in inanimate objects are usually much slower and less efficient that reactions taking place in animate beings. Almost all the chemical reactions in biological systems are responsible for a particular function of the organism and hence are highly efficient.

The mechanisms by which reactions occur also differ. In non-living objects, chemical reactions take the agency of catalysts. Catalysts are chemicals which alter the rate of a chemical reaction by increasing or decreasing the activation energy of the reaction.

On the other hand, chemical reactions in biological systems require an enzyme to work. The enzyme is a chemical species which attaches to the chemical substrate and on a particular tissue and brings about a conversion of the substrate to the desired product. The enzyme is recovered at the end of the reaction.

3. Catalysts are chemical species which alter the rate of chemical reaction. Catalysts lower the activation energy barrier for a reaction and speed up the rate of the reaction. Catalysts remain unchanged during the course of the reaction and can be recovered at the end of the reaction.

4. Water is displaced in the graduated cylinder because of evolution of oxygen gas. Hydrogen peroxide is oxidized to oxygen, which displaces water and occupies volume in the graduated cylinder.

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