Question

Enzymes PEP carboxylase and RuBP carboxylase are located in chloroplasts of
a. $C_3$ plants
b. CAM plants
c. $C_4$ plants
d. Both B and C

Answer 1

Hint: Chloroplasts are that organelles are found in plant cells and eukaryotic algae that conduct photosynthesis. Chloroplasts absorb sunlight and then use it in conjunction with water and carbon dioxide gas to produce food for the plant. Rubisco subunit is universally encoded by the chloroplast genome.

Complete answer:
- The initial product of the assimilation in $C_3$ plants is carbon dioxide through photosynthesis is 3-phosphoglycerate, which contains 3 carbon atoms.
- RuBP carboxylase is present in $C_3$ plants.
- The majority of plants produce 3-phosphoglyceric acid (PGA) as a first product during carbon dioxide fixation. This pathway is known as the $C_3$ pathway which is also called the Calvin cycle.
- In the first step, the two molecules of PGA are produced with the help of the enzyme called RuBP carboxylase. In the subsequent steps, the ATP and NADPH phosphorylate the 3-PGA and ultimately produce glucose. Then the cycle restarts again by regeneration of RuBP.
- CAM (Crassulacean acid metabolism) plants minimize photorespiration and save water by separating these steps in time, between night and day. In this pathway, both PEP carboxylase and RuBP carboxylase are present.
- $C_4$ plants are defined as the plants that use the $C_4$ pathway or Hatch-slack pathway during the dark reaction.
- In the $C_4$ pathway, both PEP carboxylase and RuBP carboxylase are present.
- The $C_4$ pathway initiates with a molecule called phosphoenolpyruvate which is a 3-carbon molecule. This is the primary Carbon dioxide acceptor and the carboxylation takes place with the help of an enzyme, PEP carboxylase. They yield a 4-Carbon molecule called oxaloacetic acid (OAA).

Hence, the correct answer is option (D).

Note: PEP carboxylase is found in mesophyll cells of $C_4$ plants that help in the formation of oxalo acetic acid. RuBP carboxylase is found in the chloroplast of both $C_3$ and $C_4$ plants and it helps in the fixation of carbon dioxide in the Calvin cycle. In the $C_4$ cycle, yield a 4-Carbon molecule called oxaloacetic acid (OAA).