Oxidation - Reduction Reactions in Yeast

Purpose:
To demonstrate oxidation - reduction reactions in living systems

Equipment:
3 culture tubes (13 mmX 100mm)
Culture tube rack
5 ml pipette
pipette pump
2,6 dichlorophenol indophenol solution (Dipip) ( 0.2 gram in 1 liter distilled water)
yeast solution (2%)
glucose solution (5%)
NaCl solution (5%)
parafilm

Background:
Organisms have certain pathways where electrons are passed from one molecule to the next in a chain of reactions. Of course, when a molecule accepts an electron it is reduced and when it loses an electron it is oxidized. In order for ATP to be synthesized from ADP and P, energy must be transferred to ADP to allow for the attachment of the third P. This is a process which occurs continually in most cells. The pathway of electrons is necessary, since their movement through a succession of electron transport molecules allows for a transfer of protons through a membrane. This bulds up an excess of protons on one side of the (mitochondrial) membrane creating a proton gradient which can be used to do work. In this case, the work is the transfer of energy to ATP. In this laboratory activity, some of the electrons headed for this electron pathway will be intercepted by the indicator (Dipip) and turn from the blue, oxidized state to colorless which is the reduced state.

Procedure:
1. Number 3 culture tubes and add the solutions listed below to each tube.
2. Add 8-10 drops of Dipip to each tube. Cover tube with parafilm and invert 2 or 3 times to mix. Record the starting time.
3. Observe until the blue color disappears. Record the time of disappearance for each tube.

Tube 1: 5ml yeast, 10ml H2O
Tube 2: 5ml yeast, 10ml dextrose, H2O
Tube 3: 5ml yeast, 10 ml 5% NaCl

Data:
Share your results with class members. Find the class mean for each tube.

References:
http://www.blc.arizona.edu/interactive/metabolism2.95/atp.html
http://www.tayloru.edu/~bio/authorware/cell%20respiration/atpsyn.html
http://www.bio.ilstu.edu/arkins/Lecture%2021A.html
http://www.sp.uconn.edu/~terry/images/anim/ATPmito.html

Bruce Faitsch
Guilford High School
Guilford, Connecticut