Question

You would like to test the effect of Compound X, a plant extract on mitochondrial function, more precisely on the succinate dehydrogenase function. You set 5 tubes, adding the solutions indicated from the table below in each of them. Once ready, you add a mitochondrial suspension you previously prepared from bean extract to each tube. Finally, you measure the absorbances for the 5 tubes every 5 minutes for 35 minutes. You obtain the results and record then in Table 1.

Tube	Assay Medium	Azide	DPIP	Coumpound X	Succinate	Mitochondrial Suspension
Blank 1	3.4 ml	0.5 ml	---	---	0.5 ml	0.6 ml
1	2.9 ml	0.5 ml	0.5 ml	---	0.5 ml	0.6 ml
2	3.4 ml	0.5 ml	0.5 ml	---	---	0.6 ml
3	2.7 ml	0.5 ml	0.5 ml	0.2 ml	0.5 ml	0.6 ml

Table 1: Absorbance Readings (A₆₀₀) at Each Time Interval

Tube #	5 min	10 min	15 min	20 min	25 min	30 min	35 min
1	0.48	0.36	0.25	0.15	0.07	0.05	0.04
2	0.67	0.75	0.67	0.67	0.83	0.68	0.70
3	0.58	0.55	0.56	0.55	0.54	0.55	0.52

1. Which is the control tube? (1pt)
2. What is the role of DPIP? (1 pt)
3. Why does the absorbance decreases with time? (3 pts)
4. What happens if you do not add succinate to your preparation? What is the role of succinate? (3 pts)
5. How does Compound X affect the reaction rate? (5 pts)

Answer 1

Answer - Test tube no - 2 is a control

Answer - DPIP substitutes as an electron acceptor in place of NADP +. During photosynthesis, as the electrons of DPIP are being used, the blue colour of DPIP becomes colourless. Therefore, a dye-reduction experiment can be assessed, where a higher light transmittance signals active photosynthesis

Answer - According to this law, absorbance and concentration are directly proportional. If you increase the original concentration, the absorbance increases and if you dilute the solution(which means you decrease the original concentration), the absorbance will decrease in direct proportion.

Answer - Reactive oxygen species (ROS) are signalling molecules that regulate plant development and responses to stresses. Mitochondria are the source of most ROS in heterotrophic cells, and mitochondrial complex I and complex III are regarded as the main sites of ROS production in plant mitochondria. Recent studies have demonstrated that succinate dehydrogenase (SDH) also contributes to mitochondrial ROS production. However, the ability of SDH to generate ROS in plants is unclear. The aim of this study was to evaluate the role of SDH in mitochondrial ROS production.

Answer - Arabidopsis thaliana and Oryza sativa, and the induction of ROS production by specific SDH inhibitors impaired plant growth. In addition, this effect was accompanied by the down‐regulation of cell cycle genes and the up‐regulation of stress‐related genes