Question

The first pentose sugar formed in PPP of respiration in
(a) Ribulose 5-Phosphate
(b) Ribose 5-Phosphate
(c) Xylulose 5-Phosphate
(d) Deoxyribose 5-Phosphate

Answer 1

Hint: This is 1 of the end-products of the pentose phosphate pathway. It is also an intermediate, formed in the Calvin cycle. It is formed by the phosphogluconate dehydrogenase, and it can be acted on by these phosphopeptide isomerases and phosphopeptide epimerase.

Complete Step by Step answer:
The process of the pentose phosphate pathway involves the oxidation of glucose-6-phosphate to make 6-phosphogluconolactone which successively is converted into pentose phosphates. Within the initiative, glucose-6-phosphate is converted into 6-phosphogluconic acid within the presence of coenzyme $NADP$. Within the 2nd step, 6-phosphogluconolactone is then hydrolyzed to supply 6 molecules of 6-phosphogluconic acid. Within the 3rd step, 6-phosphogluconic acid is oxidatively decarboxylated by the enzyme 6-phosphogluconic acid dehydrogenase to supply 6 molecules of $CO^2$, 6 molecules of $NADPH$ are produced, and 6 molecules of ribulose-5-phosphate are produced. This is often the primary pentose sugar formed within the process. Thus, the right answer is option A.
So, the correct answer is, ‘Ribulose 5-phosphate.’

Note:
- The pentose phosphate pathway(PPP) is an alternative for the process glycolysis. It is also called as the shunt because glucose is shunted instead of going through the glycolytic pathway. Pentose phosphate pathway (PPP) plays a very important role in regulating cancer cell growth by supplying enough cells with not only ribose-5-phosphate but also NADPH for detoxification of intracellular ROS, reductive biosynthesis, and ribose biogenesis.
- The correct enzyme of the pathway is 6-phosphogluconate dehydrogenase. Subsequent breakage of the pentose phosphate typically produces glyceraldehyde 3-phosphate and acetate or acetyl phosphate (depending on the enzyme system) . The final yield of ATP for this pathway is usually just one ATP per glucose molecule.