Botany - Photosynthesis in Higher Plants Question with Solution | TestHub
The Calvin cycle proceeds in three stages:
1. Reduction, during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH.
2. Regeneration, during which the carbon dioxide acceptor ribulose-1,5-biphosphate is formed.
3. Carboxylation, during which carbon dioxide combines with ribulose-1,5-biphosphate.
Identify the correct sequence.
Options:
Answer:
Solution:
Calvin cycle (C3 cycle) occurs in three steps:
(i) Carboxylation: In the presence of Rubisco (RuBP carboxylase, most abundant protein), carbon dioxide combines with ribulose biphosphate (acceptor molecule) to form first a transitory 2-carboxy 3-keto 1,5-biphosphoribotol and then two molecules of 3-phosphoglyceric acid or PGA (first stable product).
(ii) Glycolytic reversal: With the help of ATP and triosephosphate kinase, 3-PGA is converted into 1,3-biphosphoglyceric acid. In the presence of enzyme triosephosphate dehydrogenase and NADPH, 1,3-BPGA is changed to glyceraldehyde-3-phosphate (3 phosphoglyceraldehydes). A part of glyceraldehyde-3-phosphate is changed into its isomer with the help of enzyme phophotriose isomerase. The isomer is dihydroxyacetone-3-phosphate. In the presence of enzyme aldolase, GAP and DiHAP combine giving rise to fructose-1,6-biphosphate, from which glucose and its polymers are produced.
(iii) Regeneration of RuBP: RuBP is regenerated through the formation of 4-C, 5-C and 7-C intermediates.
