Lab Respiration

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Tube 2 will contain alcohol and will give a positive result for the presence of alcohol.

You will use these tubes to interpret the results of the alcohol tests performed by the instructor.

Slide 11

CELL RESPIRATION

Introduction to the Krebs Cycle and the Action of Succinic (Acid) Dehydrogenase.

Succinic acid dehydrogenase is and enzyme that oxidizes succinic acid into fumaric acid as part of the Krebs cycle. During this reaction the coenzyme FAD is reduced to FADH2. This reaction is shown as Figure 7.4 in your lab manual.

This reaction represents a typical enzymatic reaction that involves a substrate (succinic acid), an enzyme (succinic acid dehydrogenase), and a product (fumaric acid).

We will use methylene blue as an indicator that this reaction is taking place. Methylene blue will remove the electrons from FADH2 and turn from blue to colorless. Thus we will be able to determine the rate of the reaction by noting how long it takes the methylene blue to turn from blue to clear.

Slide 12

CELL RESPIRATION

Introduction to the Krebs Cycle and the Action of Succinic (Acid) Dehydrogenase.

We will use methylene blue as an indicator that this reaction is taking place. Methylene blue will remove the electrons from FADH2 and turn from blue to colorless. Thus we will be able to determine the rate of the reaction by noting how long it takes the methylene blue to turn from blue to clear.

The methylene blue will clear as FADH2

is produced.

<====

The methylene blue

will start out blue.

===>

Slide 13

CELL RESPIRATION

Experimental procedure for The Krebs Cycle and the Action of Succinic (Acid) Dehydrogenase.

Tube 1: Place approximately 2 cm of liquid hamburger into a test tube. Then add 10 drops of succinic acid and 3 drops of methylene blue to the hamburger and mix. Note the time as you mix. This is a timed experiment and it is important to know the time the reaction started. Once the reagents are mixed do not mix them again (Your instructor will explain why). Not the time when the only blue remaining is a thin band at the surface of the reagents.

Tube 2: Place approximately 2 cm of liquid hamburger into a test tube. Then add 10 drops of distilled water instead of succinic acid and 3 drops of methylene blue to the hamburger and mix. Note the time as before and watch for the color to change.

Slide 14

CELL RESPIRATION

Experimental procedure

for The Krebs Cycle and the Action of Succinic (Acid) Dehydrogenase (cont.).

Tube 3: Place approximately 2 cm of liquid hamburger into a test tube. Then add 10 drops of malonic acid instead of succinic acid and 3 drops of methylene blue to the hamburger and mix. Note the time as before and watch for the color to change.