Question

Tylenol Case Study

In 1982, seven people near Chicago, Illinois, died soon after taking Tylenol. The symptoms that they experienced before dying were dizziness, confusion, headache, and shortness of breath. Autopsy results indicated that they died from suffocation, even though the oxygen level in their blood was above normal. The concentrations of other metabolites associated with cellular respiration were also measured and the results are shown in the table below:

Metabolite	Average Level for Victims	Normal Level
Glucose	99 μM	100 μM
Pyruvate	27 μM	25 μM
NAD+	10 μM	75 μM
NADH	400 μM	50 μM

1. According to this data, which of the major chemical reactions of cellular respiration appears to not be occurring?

Answer 1

Answer: Electron transport chain is non-functional
Explanation:
Aerobic respiration involves four major steps
i. Glycolysis
ii. transition reaction
iii. TCA cycle
iv. Electron transport chain

The first three stages produce ATP, NADH, and FADH2.
NADH and FADH2 enter the electron transport chain to produce ATP by oxidative phosphorylation.
Molecular oxygen is the terminal electron acceptor in aerobic respiration.

If Cytochrome oxidase is inhibited, electrons cannot be donated to molecular oxygen (Any defect in the electron carriers would result in the same phenotype)
This results in the reduced oxidation of NADH and FADH2 to NAD+ and FAD.
ATP cannot be produced by oxidative phosphorylation

From the given data, there is no problem with the conversion of glucose to pyruvate.
However, NADH levels are elevated and NAD+ levels are reduced.
This shows that NADH is not getting oxidized to NAD+ i.e. the electron transport chain is not functional.