Nucleotides Are Poor Sources Of Energy

Structure Azaserine

a What is the role of p-aminobenzoate in these bacteria Hint See Fig. 18-16 . b Why does AICAR accumulate in the presence of sul-fanilamide c Why are the inhibition and accumulation reversed by addition of excess p-aminobenzoate 12. Pathway of Carbon in Pyrimidine Biosynthesis Predict the locations of 14C in orotate isolated from cells grown on a small amount of uniformly labeled 14C succinate. Justify your prediction. 13. Nucleotides As Poor Sources of Energy Under starvation conditions,...

Digestion Mobilization and Transport of Fats

Cells can obtain fatty acid fuels from three sources fats consumed in the diet, fats stored in cells as lipid droplets, and fats synthesized in one organ for export to another. Some species use all three sources under various circumstances, others use one or two. Vertebrates, for example, obtain fats in the diet, mobilize fats stored in specialized tissue adipose tissue, consisting of cells called adipocytes , and, in the liver, convert excess dietary carbohydrates to fats for export to other...

Regulation of the Citric Acid Cycle

Tca Cycle Nh4

As we have seen in Chapter 15, the regulation of key enzymes in metabolic pathways, by allosteric effectors and by covalent modification, ensures the production of intermediates at the rates required to keep the cell in a stable steady state while avoiding wasteful overproduction. The flow of carbon atoms from pyruvate into and through the citric acid cycle is under tight regulation at two levels the conversion of pyruvate to acetyl-CoA, the starting material for the cycle the pyruvate...

Metabolic Fates of Amino Groups

Nitrogen, N2, is abundant in the atmosphere but is too inert for use in most biochemical processes. Because only a few microorganisms can convert N2 to biologically useful forms such as NH3 Chapter 22 , amino groups are carefully husbanded in biological systems. Figure 18-2a provides an overview of the catabolic pathways of ammonia and amino groups in vertebrates. Amino acids derived from dietary protein are the source of most amino groups. Most amino acids are metabolized in the liver. Some of...

Leptin Stimulates Production of Anorexigenic Peptide Hormones

Arcuate Nucleus Pathway

Two types of neurons in the arcuate nucleus control fuel intake and metabolism Fig. 23-33 . The orexigenic appetite-stimulating neurons stimulate eating by producing and releasing neuropeptide Y NPY , which causes the next neuron in the circuit to send the signal to the brain, Eat The blood level of NPY rises during starvation, and is elevated in both ob ob and db db mice. The high NPY concentration presumably underlies the obesity of these mice, who eat voraciously. The anorexigenic...

If Your Diet Is Rich In Alanine But Deficient In Aspartate Will You Show Signs Of Aspartate Deficiency

Holmes, F.L. 1980 Hans Krebs and the discovery of the ornithine cycle. Fed. Proc. 39, 216-225. A medical historian reconstructs the events leading to the discovery of the urea cycle. Kirsch, J.F., Eichele, G., Ford, G.C., Vincent, M.G., Jansonius, J.N., Gehring, H., amp Christen, P. 1984 Mechanism of action of aspartate aminotransferase proposed on the basis of its spatial structure. J. Mol. Biol. 174, 497-525. Morris, S.M. 2002 Regulation of enzymes of the urea cycle and arginine metabolism....