Assays of Metabolism
Content Objectives
1. Define endergonic and exergonic reactions.
2. Define oxidation, reduction.
Process Objectives
1. Apply cytochemical assays.
2. Discuss application of the tetrazolium assay.
Introduction
Chemical reactions can consume energy (endergonic) or release energy (exergonic).
Endergonic and exergonic reactions are coupled in metabolic pathways. Catabolic
reactions yield a net release of energy. Anabolic reactions require a net input of energy.
Iodine is a chemical assay for starch., a storge carbohydrate in plants. If starch is
present, it will react with iodine to produce a very dark purple color. Tetrazolium is a
chemical assay for oxidation-reductions (“redox”) reactions. In its oxidized state
(donated electrons), tetrazolium is clear; in its reduced state (accepted electrons),
tetrazolium is red.
Protocols
Chemical Reactions
Enderthermic Reaction:
Obtain 1 50 ml plastic centrifuge tube. Add about 3 gm of Ammonium chloride (NH4Cl2)
Add about 25 ml of water. Place cap on securely and shake the tube.
Exergonic Reaction:
Obtain 1 50 ml plastic centrifuge tube. Add about 3 gm of Calcium chloride (CaCl2).
Add about 25 ml of water. Place cap on securely and shake the tube.
Protocol
Assay of Oxidation-Reduction Reactions
1.
Use a razor blade to cut three corn seeds longitudinally.
2.
Place each cut corn seed in a petri dish, numbered 1-3.
3.
Add about two drops of water on seed #1.
4.
Add about two drops of iodine on seed #2.
5.
Add about two drops of Tetrazolium on seed #3; if needed, add two more
drops.
6.
Incubate the seeds at room temperature for about 15 minutes.