Which of the following is FALSE about ribose and nucleotide

Which of the following is FALSE about ribose and nucleotide and nucleic acid synthesis?

a) Ribose can be synthesized in virtually all tissues

b) Since ribose is not a significant constituent of systemic blood,tissues must satisfy their own requirement for this important precursor of nucleotides.

c) It is necessary to have a completely functioning pentose phosphate pathway for a tissue to synthesize ribose phosphates.

d) The pentose phosphate pathway provides ribose residues for nucleotide and nucleic acid synthesis.

e) Although muscle tissue contains only very small amounts of glucose-6- phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, it is capable, like most other tissues, of synthesizing ribose 5-phosphate for nucleotide synthesis by a reversal of the nonoxidative phase of the pentose phosphate pathway utilizing fructose 6-phosphate.

Solution

a) True: Ribose sugar is formed by Pentose Phosphate Pathway. But high PPP following cells and more enzymes for PPP are found in liver, adipose tissue, adrenal cortex, testis, lactating mammary glands, erythrocytes, neutrophils and macrophasges.

b) False: Ribose if formed in blood cells.

c) True: As PPP will give Ribose-5 phosphate which in turn will form 5-phosphoribosyl-1-pyrophosphate. This will form IMP (hypoxanthine. IMP will then on reaction form AMP and GMP (Nucleotides). Therefore initial requirement of proper functioning is mandatory to produce Ribose phosphate.

d) True: The PPP pathway gives Ribose-5 phosphate which in turn will form 5-phosphoribosyl-1-pyrophosphate. This will form IMP (hypoxanthine. IMP will then on reaction form AMP and GMP (Nucleotides) and binding of two more Phosphates will form ATP and GTP.

e) True: The last step in PPP is formation of glyceraldehyde-3-phosphate and fructose 6-phosphate. This is non-oxidative phase (only rearrangement of carbon atoms) and also reversible. Therefore, synthesis from F6P is possible.