NEET 2025 Botany Question 131 Solution

Enzymes can be simple proteins or conjugated holoenzymes consisting of a protein part (apoenzyme) and a non-protein part (co-factor):

• • Co-factors are of three types: prosthetic groups, co-enzymes, and metal ions.
• • Prosthetic groups are organic compounds characterized by being tightly or permanently bound to the apoenzyme.

NCERT explicitly cites Catalase and Peroxidase as the prime examples:

• • Catalase catalyzes the rapid decomposition of hydrogen peroxide into water and molecular oxygen: $2 H_2O_2 \xrightarrow{\text{Catalase}} 2 H_2O + O_2$.
• • Haem (an iron-protoporphyrin complex) is the prosthetic group tightly integrated into the catalytic active site of catalase.
• • The central iron ($Fe^{3+}/Fe^{4+}$) undergoes reversible redox changes during the catalytic cycle.

Reviewing the other candidate enzymes:

• • RuBisCo: Requires $Mg^{2+}$ as an essential divalent activator ion.
• • Carbonic anhydrase: Contains a zinc ($Zn^{2+}$) metal ion at its active site, not haem.
• • Succinate dehydrogenase: Uses FAD (flavin adenine dinucleotide) and iron-sulfur clusters ($Fe-S$), but not haem as its prosthetic group.

Catalase is the enzyme containing haem as its prosthetic group, matching Option (4).