Electron Transport Chain Experiment

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LAB REPORT PLANT BIOCHEMSITRY (SAP 1123)

EXPERIMENT 4: ELECTRON TRANSPORT CHAIN

DATE: 22/2/2017

GROUP 7

NAME OF LECTURER: Asst. Prof. Dr. SAHENA FERDOSH

SEMESTER: SEM 2 16/17

OBJECTIVE

1. To indirectly measure photosynthesis by observing rate of electron transfer.

2. To demonstrate that the dark reaction is a separate and independent event from light reaction.

INTRODUCTION

         Photosynthesis is the process in which light energy is converted to chemical energy in the form of sugars. In a process driven by light energy, glucose molecules or other sugars are constructed from water and carbon dioxide, and oxygen is released as a byproduct. The glucose molecules provide organisms with two crucial resources which are energy and fixed-organic-carbon. Photosynthesis consists of two reactions which includes the light-dependent reaction and dark reaction.

        The light-dependent reactions take place in the thylakoid membrane and require a continuous supply of light energy. Chlorophylls absorb this light energy, which is converted into chemical energy through the formation of two compounds, ATP and NADPH. In this process, water molecules are also converted to oxygen gas.

         The Calvin cycle, also called the dark reactions, takes place in the stroma and does not directly require light. Instead, the Calvin cycle uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide and produce three-carbon sugars—glyceraldehyde-3-phosphate, or G3P.

         In the experiment performed, 2, 6-dichlorophenol-indolephenol (DCPIP) was added to chloroplast cells, which replaced the NADP+ along the electron transport chain. DCPIP is an alternate electron acceptor and functions in the experiment to transfer electrons. DCPIP is a dye which is dark blue in color when oxidized and colorless when reduced. The rate of DCPIP decoloration depends on its concentration and the rate of electron flow. Thus, by using DCPIP as an artificial electron-acceptor, electron transfer can be monitored in the absence of carbon dioxide fixation.

PROCEDURE

1. Label the test tube
2. Add the buffer and water to each test tube
3. Add 0.5ml of chloroplast mixture (test tube 1,2,4)
4. Add 0.5ml of DCPIP as the last step (test tube 2,3,4)
5. Cap all the test tube
6. Wrap test tube 4 only with aluminium foil
7. Mix the contents of each tube
8. Record the colours of each test tube before place it in front of the light
9. Keep an eye for the test tube within 5 minutes
10. Record the colours after the test tube place in front of the light
11. Record expectations for each tube while wait

RESULTS (Table 4.2)

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