Fatty acid degradation and

Figure 17-20 The interlocking pathways of glycolysis, gluconeogenesis, and fatty acid oxidation and synthesis with indications of some aspects of control in hepatic tissues. (— ) Reactions of glycolysis, fatty acid degradation, and oxidation by the citric acid cycle. ) Biosynthetic pathways. Some effects of insulin via indirect action on enzymes , 0, or on transcription 0/ 0. Effects of glucagon , .

Mitochondria have an inner and an outer membrane separated by the intermembrane space. The outer membrane is more permeable than the inner membrane due to the presence of porin proteins. The inner membrane, which is folded to form cristae, is the site of oxidative phosphorylation, which produces ATP. The central matrix is the site of fatty acid degradation and the citric acid cycle. 

Fatty acid degradation and synthesis are relatively simple processes that are essentially the reverse of each other. The process of degradation converts an aliphatic compound into a set of activated acetyl units (acetyl CoA) that can be processed by the citric acid cycle (Figure 22.2). An activated fatty acid is oxidized to introduce a double bond the double bond is hydrated to introduce an oxygen the alcohol is oxidized to a ketone and, finally, the four carbon fragment is cleaved by coenzyme A to yield acetyl CoA and a fatty acid chain two carbons shorter. If the fatty acid has an even number of carbon atoms and is saturated, the process is simply repeated until the fatty acid is completely converted into acetyl CoA units. 

Figure 22.2. Steps in Fatty Acid Degradation and Synthesis. The two processes are in many ways mirror images of each other. 

We have encountered this mode of activation in fatty acid degradation and will see it again in lipid and protein synthesis. 

Various tiny structures, so-called organelles, are embedded in the cytoplasm where they make numerous cell functions possible, (s. fig. 2.9) (s. tab. 2.1) The enzyme-rich mitochondria have an outer and an inner membrane, with the latter forming creases (cristae). The outer membrane is relatively permeable for small molecules. However, the inner membrane (which surrounds the matrix) must use specific transport proteins to enable protons, calcium, phosphate and so on to pass. Energy-rich substrates are transformed into ATP in the mitochondria. The enzymes which are responsible for fatty-acid degradation and the citric-acid cycle can be found in the matrix. The inner membrane also contains the enzymes of the so-called respiratory cycle. An enormous number of energy-providing reactions and metabolic processes take effect at this site. They have a round-to-oval shape with a diameter of about 1 im. There are 1,400-2,200 mitochondria per liver cell (18-22% of the liver cell volume). They generally lie in... 

Fatty Acid Degradation and Synthesis Mirror Each Other in Their Chemical Reactions... 

For the majority of obese humans, who produce leptin, perhaps a genetic defect exists in the leptin receptor. Or perhaps the genetics of obesity in humans is more complex than in mice. Clearly lipid metabolism in animals is a complex process and is not yet fully understood. The discovery of the leptin gene, and the hormone it produces, is just one part of the story. In this chapter we will study other aspects of Upid metaboUsm the pathways for fatty acid degradation and biosynthesis and the processes by which dietary lipids are digested and excess Upids are stored. 

What molecules involved in fatty acid degradation and fatty acid biosynthesis contain the phosphopantetheine group ... 

In this chapter we attempted to review the transcriptional regulation of fatty acid metabolism in the liver. Many transcription factors are involved in this process. We chose to focus on PPARa and SREBP-lc because of their established regulatory roles in the control of transcriptional programs that govern fatty acid degradation and synthesis, respectively. Moreover, we thought their distinct activation processes and sensitivity to various stimuli make them very... 

As is trne in the opposing processes of glycolysis and glnconeogenesis, the pathways for the opposing processes of fatty acid degradation and fatty acid synthesis are not simply the reverse of each other. The processes are separate from each other, utilize different enzyme systems, and are even located in different cellnlar compartments. Degradation by the (3-oxidation pathway takes place in cellular mitochondria, whereas biosynthesis of fatty acids occnrs in the cytoplasm. 

Derivatives of CoA occur as intermediates in the P-oxidation of fatty acids (see Fatty acid degradation) and in the synthesis of some alkaloids. 

CYP505 CO-1 to CO-3 fatty acid hydroxylations (P450foxy) and fumonisin C14 and CIS hydroxylations Fatty acid degradation and fumonisin biosynthesis F. oxysporum and F. verticillioides [504, 693, 694] [840, 841]... 

Dihal AA, van der Woude H, Hendriksen PJ, Charif H, Dekker LJ, Ijsselstijn L, de Boer VC, Alink GM, Burgers PC, Rietjens IM, Woutersen RA, Stierum RH (2008) Transcriptome and proteome profiling of colon mucosa from quercetin fed F344 rats point to tumor preventive mechanisms, increased mitochondrial fatty acid degradation and decreased glycolysis. Proteomics 8 45-61... 

Fatty acids are oxidized completely to CO2 and water by )8-oxidation and the citric acid cycle. Acetyl CoA is the end product of )8-oxidation of fatty acids and is the source of carbon for fatty acid biosynthesis. Yet, the pathways for fatty acid degradation and synthesis are so very different that they even occur within different compartments within cells. Fatty acid synthesis takes place in the cytoplasm of animal cells and in the plastids of plant cells, whereas )8-oxidation is located in mitochondria in both animal and plant cells. 

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