28) The first (and most critical) step of the Calvin-Benson Cycle involved in CO

Question

28) The first (and most critical) step of the Calvin-Benson Cycle involved in CO2 fixation in many microbes, including cyanobacteria, is catalyzed by which of the following enzymes: a. Nitrogenase b. Methyl reductase c. RuBisCO d. APS kinase e. ATP sulfurylase 29) Proteorhodopsin & bacteriorhodopsin proteins provide energy to photoheterotrophs. These proteins function as: a. Photoprotective proteins b. Light-driven proton pumps c. Redox shuttles for anoxygenic photosynthesis d. ): scavengers for anoxygenic photosynthesis e. Chlorophyll accessory pigments

Explanation / Answer

(28)

Calvin- Benson Cycle is also known as Calvin Cycle. This cycle takes place during the photosynthesis in the chloroplast in a set of chemical reactions. It is a light independent cycle as it happens when there is a capture of energy from the sunlight.

(a) Nitrogenase: These enzymes are helpful in the conversion of atmospheric N2 in the useful products during the biological nitrogen fixation by some organisms. Hence, option (a) is incorrect.

(b) Methyl Reductase: this enzyme is produced by the MTHFR gene and it plays its role in the methyl cycle. Hence, option (b) is incorrect.

(d) APS kinase: This enzyme along with ATP Sulfurylase is helpful in PAPS synthesis in fungi, bacteria and plants. Hence, option (d) is incorrect.

(e) ATP Sulfurylase: This enzyme helps by catalyzing the sulfate activation. It transfers the sulfate to ADP (Adenine Monophosphate) to form the APS (Adenosine 5' phosphosulfate) and PPi (Pyrophosphate). Hence, option (e) is incorrect.

Correct Answer is option (c): RuBisCO

Reason: Ribulose-1,5- Bisphosphate carboxylase/oxygenase enzyme is also called as RuBisCO. It takes part in the very first most important and critical step of this Calvin cycle and helps in fixing of atmospheric CO2 in an organic molecule which further undergoes the 2 more stages of calvin cycle to produce energy rich compounds. Hence. option (c) is correct.

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