### Passage I Researchers investigated the regulation of the electron transport chain (ETC… — ACT

### Passage I

Researchers investigated the regulation of the electron transport chain (ETC) in isolated mammalian mitochondria by measuring the rate of oxygen ( $O_2$ ) consumption (in $\text{nmol } O_2/\text{min}/\text{mg protein}$ ) under different biochemical conditions.

In all trials, a fixed concentration of isolated mitochondria was suspended in a reaction chamber containing a physiological buffer solution at $37^\circ\text{C}$ . The baseline concentration of dissolved $O_2$ in the buffer was monitored. Respiration substrates, adenylates, and metabolic inhibitors were added sequentially or in combination to study their effects on the rate of mitochondrial $O_2$ consumption. The components added to each trial are shown in Table 1.

### Table 1

Trial	Mitochondria	Succinate (substrate)	ADP	Oligomycin (ATP synthase inhibitor)	FCCP (proton gradient uncoupler)
1	Yes	Yes	No	No	No
2	Yes	Yes	Yes	No	No
3	Yes	Yes	Yes	Yes	No
4	Yes	Yes	Yes	Yes	Yes
5	Yes	No	Yes	No	No
6	No	Yes	Yes	No	Yes

An investigator wants to establish a baseline condition to prove that the decrease in dissolved $O_2$ in Trials 1–5 is due to the biological activity of the electron transport chain in the mitochondria, rather than abiotic chemical reactions or gas leakage from the reaction chamber. Which of the trials listed in Table 1 serves as the most appropriate control group for this purpose?

A
Trial 1, because it contains mitochondria and succinate but lacks ADP, isolating resting state respiration.
B
Trial 5, because it contains mitochondria and ADP but lacks succinate, isolating the respiration fueled by endogenous substrates.
Trial 6, because it lacks mitochondria but contains all other components, isolating biological oxygen consumption from abiotic processes or gas leaks.Cevap
D
Trial 3, because it contains oligomycin to halt ATP synthase, serving as a baseline for the proton leak rate.

Cevap

Trial 6 serves as the most appropriate control group because it lacks the biological component (mitochondria) while retaining the chemical substrates, uncoupler, and physical conditions, thereby isolating any potential abiotic oxygen consumption or apparatus leakage.

The trial that lacks mitochondria but contains the other reaction components serves as the appropriate negative control. If any oxygen decrease occurs in this setup, it must be due to abiotic oxidation or chamber leakage. Comparing the rates of Trials 1–5 to this baseline allows the investigator to isolate the oxygen consumption directly caused by biological mitochondrial activity.

Adım Adım Çözüm

Identify the confounding variables that need to be controlled based on the investigator's goal.

The investigator needs to prove that the oxygen consumption is due to biological mitochondrial respiration, rather than abiotic chemical reactions or gas leakage.

This requires identifying a baseline or negative control setup that removes the biological component (mitochondria) while keeping all other potential variables constant.

Examine the composition of the trials in Table 1 to find a setup that isolates mitochondrial biological activity.

Trial 6 contains the substrate (succinate), the phosphate acceptor (ADP), and the uncoupler (FCCP), but does not contain any mitochondria.

By omitting the mitochondria, any oxygen depletion measured in Trial 6 must be due to abiotic factors or leaks, establishing the non-biological baseline rate.

Compare the proposed trial to other potential baselines to confirm it is the correct control group.

Trial 6 is the only trial without mitochondria, whereas Trials 1 and 5 contain mitochondria but test physiological variables (lack of ADP and substrate, respectively).

Only a trial completely lacking mitochondria can isolate biological activity from abiotic oxygen loss.

Anahtar Kavram

Determining Control Groups and Baseline Conditions

Tahmini Süre:2m 0s

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru

Trial	Mitochondria	Succinate (substrate)	ADP	Oligomycin (ATP synthase inhibitor)	FCCP (proton gradient uncoupler)
1	Yes	Yes	No	No	No
2	Yes	Yes	Yes	No	No
3	Yes	Yes	Yes	Yes	No
4	Yes	Yes	Yes	Yes	Yes
5	Yes	No	Yes	No	No
6	No	Yes	Yes	No	Yes

Trial	Mitochondria	Succinate (substrate)	ADP	Oligomycin (ATP synthase inhibitor)	FCCP (proton gradient uncoupler)
1	Yes	Yes	No	No	No
2	Yes	Yes	Yes	No	No
3	Yes	Yes	Yes	Yes	No
4	Yes	Yes	Yes	Yes	Yes
5	Yes	No	Yes	No	No
6	No	Yes	Yes	No	Yes

Trial	Mitochondria	Succinate (substrate)	ADP	Oligomycin (ATP synthase inhibitor)	FCCP (proton gradient uncoupler)
1	Yes	Yes	No	No	No
2	Yes	Yes	Yes	No	No
3	Yes	Yes	Yes	Yes	No
4	Yes	Yes	Yes	Yes	Yes
5	Yes	No	Yes	No	No
6	No	Yes	Yes	No	Yes