A deficiency of substance Folate can result in an anemia. Choose the type of anemia that would occur if the substance were deficient.
Correct Answer: Megaloblastic anemia
Description: a. The 1-carbon groups that FH4 receives are transferred to various compounds (see Figure I below, steps 5 to 8).(1). Purine precursors obtain carbons 2 and 8 from FH4 . Purines are required for DNA and RNA synthesis.(2). dUMP forms dTMP by accepting a 1-carbon group from FH4 (Figure II). This reaction produces the thymine required for DNA synthesis.(a). The methylene group is reduced to a methyl group in this reaction, and FH4 is oxidized to FH2 .(b). FH2 is reduced to FH4 in the NADPH-requiring reaction catalyzed by FH2 reductase.(3). Glycine obtains a 1-carbon group from FH4 to form serine.(4). Vitamin B12 obtains a methyl group from 5-methyl-FH4 . The methyl group is transferred from methyl-B12 to homocysteine to form methionine (see Figure III, reaction 8). This is the only fate of 5-methyl-FH4 .Folate deficiency results in a megaloblastic anemia because of decreased production of purines and the pyrimidine thymine. Thus, lack of folate causes decreased DNA synthesis. In contrast with a vitamin B12 deficiency, neurologic problems do not occur in a folate deficiency. A hypochromic, microcytic anemia can result from the lack of iron, or lack of pyridoxal phosphate. Both conditions lead to a reduction in the synthesis of heme, so the red cells cannot carry as much oxygen (which gives them the pale color). The cells are small in order to maximize the concentration of hemoglobin present in the cells. Hemolytic anemia occurs when the red cell membrane fragments, which can occur with pyruvate kinase deficiencies or a lack of glucose-6-phosphate dehydrogenase activity (which results in reduced NADPH levels). Sickle cell anemia is caused by a point mutation in the b-globin gene, substituting a valine for a glutamic acid.I. The sources of carbon (1 to 4) for the FH4 pool and the recipients of carbon (5 to 8) from the pool. ATP, adenosine triphosphate; dUMP, deoxyuridine monophosphate; dTMP, deoxythymidine monophosphate; FH2 , dihydrofolate; FH4 , tetrahydrofolate; NAD, nicotinamide adenine dinucleotide; NADP, nicotinamide adenine dinucleotide phosphate; NADPH, reduced NADP; Pi, inorganic phosphate; PPi, pyrophosphate.II. The transfer of a 1-carbon unit from serine to deoxyuridine monophosphate (dUMP) to form deoxythymidine monophosphate (dTMP). FH4 is oxidized to FH2 in this reaction. FH2 is reduced to FH4 by dihydrofolate reductase. The rectangles indicate the steps at which the antimetabolites methotrexate and 5-fluorouracil act. FH2 , dihydrofolate; FH4 , tetrahydrofolate; NADP, nicotinamide adenine dinucleotide phosphate; NADPH, reduced NADP.III. The decarboxylation of glutamate to form GABA. PLP, pyridoxal phosphate. GABA, g-aminobutyric acid.
Category:
Biochemistry
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