IMAT 2020 Q31 [Catabolism]

Which one of the following is an example of catabolism in healthy human cells?

A. formation of RuBisCo
B. replication of DNA
C. oxidation of NADH
D. ATP made during glycolysis
E. attachment of tRNA to mRNA


The correct answer is C.

What is catabolism ?

It is a process through which a complex molecule is broken down into a simpler one or is degraded.

Based on this definition alone, we can already eliminate the following items :

  1. replication of DNA
  2. attachment of tRNA to mRNA

Now, let’s review each item one by one

  1. Formation of RuBisCo : it is a protein that helps assimilate CO2 from the atmosphere into organic matter that can be used as a source for carbon. It is found in chloroplasts is obtained through the Calvin cycle :

    • 1st phase is the reduction of 3-phosphoglycerate
    • 2nd phase the regeneration of ribulose
    • 3rd phase is carbon fixation

    It does NOT fit the definition of “catabolism” (the end molecule is more complex than the staring one).

  2. The oxidation of NADH is shown by the following reaction : NADH → NAD+ + H+ +2e-.

    It is a loss of electrons, and is therefore a form of catabolism.

  3. ATP made during glycolysis : it is made through the phosphorylation of ADP, thus turning it into a more complex molecule.

    It does NOT fit the definition of “catabolism”.