Question

specify how pentose sulphate is a CO2 acceptor in dark reaction of photosynthesis?? ​

Answer 1

Answer:

The carbon-fixing reaction of photosynthesis involves a cyclic series of reactions, often called as the Calvin cycle or C_3C3 pathway. In carboxylation or fixation, three molecules of CO_2CO2 combine with three molecules of 5C compound called ribulose-1, 5- bisphosphate (RuBP), which is the acceptor molecule of CO_2CO2, giving rise to an unstable 6- carbon compound. Carboxylation of a molecule of CO_2CO2 to RuBP is catalyzed by the enzyme RuBP carboxylase or Rubisco. The resulting 6C compound is highly unstable. This molecule quickly breaks down to give two molecules of 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA).

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Answer 2

Answer:

Reductive pentose phosphate cycle (the Calvin-Benson-Bassham cycle)

The reductive pentose phosphate cycle is the predominant pathway of carbon fixation on Earth, used by all oxygenic photosynthetic organisms, including cyanobacteria, land plants, and algae (Table 4.2). It is also the pathway of carbon fixation for purple anoxygenic phototrophs as well as numerous chemolithoautotrophic and mixotrophic organisms of the bacterial domain, including sulfide oxidizers, nitrifiers, and various iron oxidizers (Fuchs, 1989; Buchanan, 1992; Tabita, 1995). The reductive pentose phosphate pathway has also been found active among members of the anoxygenic photosynthetic genus Oscillochloris, located within the deep-branching phylum Chloroflexi (Pierson, 2001). Rubisco (ribulose-1,5-bisphosphate carboxylase⧸oxygenase) activity (Rubisco is the key enzyme in the reductive pentose phosphate cycle; see below) has also been identified among some aerobic halophilic Archaea (Altekar and Rajagopalan, 1990), although little is known about the role of Rubisco in these organisms and whether it is linked to active CO2 fixation. A gene encoding for a primitive form of Rubisco also has been found among the genome of several strictly anaerobic members of the Archaea (see Tabita, 1999) and among the green sulfur phototrophs (Chlorobium sp.) (Hanson and Tabita, 2001). These Rubisco-like proteins, however, are apparently not involved in CO2 fixation.