* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chem 454: Regulatory Mechanisms in
Survey
Document related concepts
Oxidative phosphorylation wikipedia , lookup
Lipid signaling wikipedia , lookup
Microbial metabolism wikipedia , lookup
Metalloprotein wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Peptide synthesis wikipedia , lookup
Plant nutrition wikipedia , lookup
Butyric acid wikipedia , lookup
Specialized pro-resolving mediators wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Biosynthesis wikipedia , lookup
Citric acid cycle wikipedia , lookup
Biochemistry wikipedia , lookup
Glyceroneogenesis wikipedia , lookup
Transcript
Chem 454: Regulatory Mechanisms in Biochemistry Additional Problems – Chapter 22 1. The oxidation by microbes of long-chain alkanes, which are found in crude oil, is the subject of study because of concern about oil spills. In many bacteria, alkane, oxidation occurs within the outer membrane. A monooxygenase enzyme uses molecular oxygen and an oxidizable substrate, such as NADH, to convert an alkane to a primary alcohol. Studies show that three additional reactions are required for the primary alcohol to under bg oxidation. Propose a pathway for the conversion of a long-chain primary alcohol to a substrate that can undergo b oxidation. Include cofactors and electron acceptors that might be required. 2. Malonyl-CoA, labeled with 14C in the methylene carbon, is used in excess as a substrate in a system in vivo for the synthesis of palmitoyl-CoA, which is catalyzed by a yeast fatty acid synthase complex. Acetyl-CoA and other substrates are also present in the system, but acetyl-CoA carboxlyase is not. Which carbons in palmitoyl-CoA will be labeled? 3. A deficiency of carnitine acyltransferase I in human muscle causes cellular damage and recurrent muscle weakness, especially during fasting or exercise. A deficiency of the enzyme in the liver causes an enlarged and fatty liver, hypoglycemia, and a reduction in the levels of ketone bodies in blood. Explain the likely causes of these symptoms. 4. a. Describe how malonyl-CoA affects the balance between the rates of synthesis and b oxidation of fatty acids in a liver cell. b. Show that failure to regulate theses two processes reciprocally could result in the wasteful hydrolysis of ATP. 5. 6. Plant seeds contain triacylglycerols in organelles called spherosomes. During germination, lipases located in the spherosome membrane convert triacylglycerol to monoacylglycerols, free fatty acids, and glycerol. Both free fatty acids and monoacylglycerols enter the glyoxysome (see p 485 in your text), whereas most of the glycerol is metabolized in the plant cell cytosol. A membrane-bound lipase in the glyoxysome converts monoacylglycerols to free fatty acids and glycerol. a. Describe two possible metabolic fates of glycerol in the cytosol. b. What is the fate of fatty acids in the glyoxysome? c. When a germinating plant begins to carry out photosynthesis, the number of glyoxysomes in the germinating plant decreases rapidly. Why? d. A difference between plant glyoxysomes and plant mitochondria is that glyoxysomes cannot oxidize acetyl-CoA, whereas mitochondria can. How is this observation related to the metabolism of fatty acids in these two organelles. People concerned about obesity must pay attention not only to triacylglycerol intake but also to the consumption of starch, glucose, and other carbohydrates. Although carbohydrates can be converted to glycogen in liver, muscle, and other tissues, only about 1 five percent of the energy stored in the body is present as glycogen. What happens to most carbohydrates that are consumed in excess of caloric need? 7. Wakil's pioneering studies on fatty acid synthesis included the crucial observation that bicarbonate is required for the synthesis of palmitoyl-CoA. He was surprised to find that very low levels of bicarbonate could sustain palmitate synthesis; that is, there was no correlation between the amount of bicarbonate required and the amount of palmitate produced. Later he also found that 14C-labeled bicarbonate is not incorporated into palmitate. Explain these observations. 8. In tissue culture, cells that are deficient in NADP+-linked malate enzyme can be isolated. They exhibit a slightly lower rate of fatty acid synthesis when compared with normal cells. However, cells lacking citrate lyase are very difficult to isolate. Why? 9. Hydrogenating oils to saturate the double bounds in their fatty acids in order to increase their melting temperatures causes some of the cis double bonds to convert into the trans conformation. Predict what would happen if a monoenoic fatty acid with a trans-∆10 bond were produced, ingested, and degraded by the b-oxidation pathway. If another of the ingested fatty acids contains a cis-∆11 double bond, what would be the out come of these processes? What effect would the presence of the double bond have on the yield of ATP obtained by the b oxidation of these fatty acids? 10. Certain desert mammals can survive long periods of drought by consuming plants and seeds and then generating water by metabolizing the fuels they provide. a. Briefly describe how water is generated through intermediary metabolism. Include the sources of oxygen and hydrogen, and describe reactions that lead to the formation of water. b. While parts of mature plants are a reliable source of carbohydrates and proteins, plant seeds contain high quantities of triacylglycerols and free fatty acids. Would plants or seeds be better for generating metabolic water? Why? 11. Compare the effects of high levels of intracellular citrate on pathways of fatty acid and carbohydrate metabolism. Explain how its transport from the mitochondrion to the cytosol is essential for the action of citrate on both sets of pathways. 12. In mammals, acetyl-CoA from fatty acid oxidation cannot be used for the net synthesis of pyruvate or oxaloacetate, which in turn means that net glucose synthesis from acetyl-CoA is impossible. However, glucose can be radioactively labeled when 14C-labeled acetate is introduced into human tissue culture cells and converted to acetyl-CoA by acetyl-CoA synthetase. Radioactive fatty acids can also be used to label glucose. Why? If the methyl carbon of acetate is labeled, where will glucose be labeled? 2