Have a look at the diagram below. What molecules/enzymes do 1, 2, 3 and 4 represent?

Question

BlackTom AI · Accepted Answer

To tackle this diagram question, I will evaluate each option by matching the labeled parts (1–4) with the known roles of the enzymes and molecules in the reactive oxygen species (ROS) detoxification pathway.

Option a: '1= superoxide dismutase, 2=glutathione oxidase, 3=glutathione reductase, 4= superoxide'
- Here, 1 being superoxide dismutase is reasonable, but 2 is labeled as glutathione oxidase and 3 as glutathione reductase, which do not align with the diagram components shown (the diagram labels 2 as a whole molecule consistent with hydrogen peroxide, not an enzyme). Also 4 as superoxide is incorrect because 4 corresponds to a product of the pathway, not a reactant/enzyme. Overall, this option mismatches the actual species and enzymes depicted and is inconsistent with the flow of ROS scavenging.

Option b: '1= catalase, 2=glutathione reductase, 3=glutathione peroxidase, 4= superoxide dismutase'
- The sequence here places catalase at position 1, but the diagram clearly shows the initial step producing or handling superoxide, which is the role of superoxide dismutase, not catalase. Glutathione reductase and superoxide dismutase roles are also shuffled relative to the depicted steps, and the final label of 4 as superoxide contradicts the diagram where 4 is a downstream product (likely water or oxygen). This option is not consistent with the pathway in the image.

Option c: '1=superoxide dismutase, 2=hydrogen peroxide, 3=glutathione peroxidase, 4=catalase'
- This aligns with the standard ROS detox pathway shown: step 1 corresponds to superoxide dismutase converting O2•− to H2O2, step 2 corresponds to hydrogen peroxide accumulation, step 3 involves glutathione peroxidase reducing H2O2 using glutathione, and step 4 corresponds to catalase decomposing H2O2 into water and oxygen. The diagram labels 1 as SOD activity, 2 as H2O2, 3 as the enzyme activity of glutathione peroxidase, and 4 as catalase action, matching the canonical sequence.

Option d: '1= catalase, 2=glutathione oxidase, 3=glutathione reductase, 4= superoxide dismutase'
- This arrangement places catalase at the first step, which would imply direct breakdown of H2O2 at the initial stage, not the generation or handling of superoxide in the first step. The other components (glutathione oxidase, glutathione reductase, and superoxide dismutase) do not correspond to the depicted flow of species in the diagram. Thus, this option mislabels both enzymes and reactive species relative to the shown pathway.

Overall, comparing all options, option c provides the correct mapping that follows the ROS detoxification sequence depicted: 1 is superoxide dismutase, 2 is hydrogen peroxide, 3 is glutathione peroxidase, and 4 is catalase.

PHR1122 S2 2025 PA Tox CYL

Have a look at the diagram below. What molecules/enzymes do 1, 2, 3 and 4 represent?

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