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Ch04

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Ch04

  1. 1. Chapter 4
  2. 2.  Fatty acids have 4 major roles in the cell:  Building blocks of phospholipids and glycolipids  Added onto proteins to create lipoproteins, which targets them to membrane locations  Fuel molecules - source of ATP  Fatty acid derivatives serve as hormones and intracellular messengers
  3. 3.  The oxidation of f.acids – source of energy in the catabolism of lipids Both triacylglycerols and phosphoacylglycerols have f.acids as part of their covalently bonded structures The bond between the f.acids and the rest of the molecule can be hydrolyzed (as shown in the fig.) Fig. 21-1, p.569
  4. 4. Fig. 21-2, p.569
  5. 5. p.569
  6. 6. Fig. 21-3, p.570
  7. 7. • Fatty acids oxidation begins with activation of the molecule.• A thioester bond is formed between carboxyl group of f.acid and the thiol group of coenzyme A (CoA- SH) (esterification reaction – in cytosol)
  8. 8. Fig. 21-5, p.571
  9. 9. Fig. 21-6, p.572
  10. 10.  When a f.acid with an even number of C atoms undergoes successive rounds of β-oxidation cycle, the product is acetyl-CoA. No. of molecules of acetyl-CoA produced = ½ the no. of C atoms in the original f.acid. (as shown in fig above) The acetyl-CoA enters the TCA cycle (the rest of oxidation to CO2 and H2O taking place via TCA cycle and ETC) β-oxidation takes place in mitochondria.
  11. 11.  The energy released by the oxidation of acetyl-CoA formed by β-oxidation of f.acids can be used to produce ATP. There are two sources of ATP:  Reoxidation of the NADH and FADH2 produced by β-oxidation  ATP production from processing acetyl-CoA via TCA cycle and oxidative phosphorylation NADH and FADH2 produced by β-oxidation and TCA cycle enter ETC and ATP produced through oxidative phosphorylation Table 21-1, p.575
  12. 12. Carbohydrate Lipids 32 moles of ATP  e.g stearic acid: 18 C atoms = produced 120 moles of produced from complete ATP oxidation of CHO (but,  Reason? glucose is 6C atoms, so 6  F.acid is all hydrocarbon except carboxyl group – x 3 = 18 C atoms. exists in highly reduced Therefore, state 32 x 3 = 96 ATP.  H2O is produced in oxidation of f.acids – can be a source of water for organisms that live in desert
  13. 13. CamelKangaroo rats p.575a
  14. 14. The catabolism of odd-carbon f.acids Fig. 21-8, p.576
  15. 15. The catabolism of unsaturated f.acidsThe oxidation ofunsaturated f.acidsdoes not generate asmany ATPs as it wouldfor a saturated f.acids(same C atoms) – thepresence of doublebond• the acyl-deH2asestep skipped – fewerFADH2 will beproduced
  16. 16. Fig. 21-9b, p.577
  17. 17. Fig. 21-10a, p.578
  18. 18. Fig. 21-10b, p.578
  19. 19.  Substances related to acetone (“ketone bodies”) are produced when an excess of acetyl-CoA arises from β-oxidation Occurs because when there are not enough OAA to react with acetyl-CoA in TCA cycle When organisms has a high intake of lipids and low intake of CHO or starvation and diabetes The reactions that result in ketone bodies start with the condensation of two molecules of acetyl- CoA to produce acetoacetyl-CoA
  20. 20. • the odor of acetone can be detected on thebreath of diabetics whose not controlled bysuitable treatment• Acetoacetate and β-hydroxybutyrate areacidic, their presence at high [ ] overwhelmsthe buffering capacity of the blood• to lowered the blood pH is dealt byexcreting H+ into the urine, accompanied byexcretion of Na +, K + and water → results insevere dehydration and diabetic coma• synthesis of ketone bodies in livermitochondria• transport ketone bodies in the bloodstream;water soluble• other organs such as heart muscle andrenal cortex can use ketone bodies(acetoacetate) as the preferred source ofenergy• even in brain, starvation conditions lead tothe use of acetoacetate for energy
  21. 21.  The anabolic reaction takes place in cytosol Important features of pathway:  Intermediates are bound to sulfhydral groups of acyl carrier protein (ACP); intermediates of β-oxidation are bonded to CoA  Growing fatty acid chain is elongated by sequential addition of two-carbon units derived from acetyl CoA  Reducing power comes from NADPH; oxidants in β- oxidation are NAD+ and FAD  Elongation of fatty acid stops when palmitate (C16) is formed; further elongation and insertion of double bonds carried out later by other enzymes
  22. 22. Step 1 Fig. 21-12, p.581
  23. 23. Step 2 Fig. 21-13, p.581
  24. 24. Malonyl-CoA inhibitscarnitine acyltransferase I Fig. 21-14b, p.582
  25. 25. Pathway ofpalmitate synthesisfrom acetyl-CoAand malonyl-CoAThe biosynthesis off.acids involves thesuccessive additionof two-carbon unitsto the growingchain.- Two of the three Catoms of themalonyl group ofmalonyl-CoA areadded to thegrowing fatty-acidchain with eachcycle of thebiosyntheticreaction Fig. 21-15, p.583
  26. 26. Fig. 21-15a, p.583
  27. 27. Step 3 Fig. 21-15b, p.583
  28. 28. Step 4 This reaction require multienzyme complex : fatty acid synthase Fig. 21-15c, p.583
  29. 29. Fig. 21-16, p.584
  30. 30. There are several additional reactions required for the elongationof f.acid chain and the introduction of double bonds. Whenmammals produce f.acids with longer chains than that ofpalmitate, the reaction does not involve cytosolic f-acid synthase.There are two sites for chain lengthening reactions: ER(endoplasmic reticulum) and mitochondrion. Table 21-2, p.586
  31. 31. Fig. 21-17, p.586
  32. 32. Table 21-3, p.599
  33. 33.  Lipids are transported throughout the body as lipoproteins Both transported in form of lipoprotein particles, which solubilize hydrophobic lipids and contain cell-targeting signals. Lipoproteins classified according to their densities:  chylomicrons - contain dietary triacylglycerols  chylomicron remnants - contain dietary cholesterol esters  very low density lipoproteins (VLDLs) - transport endogenous triacylglycerols, which are hydrolyzed by lipoprotein lipase at capillary surface  intermediate-density lipoproteins (IDL) - contain endogenous cholesterol esters, which are taken up by liver cells via receptor- mediated endocytosis and converted to LDLs  low-density lipoproteins (LDL) - contain endogenous cholesterol esters, which are taken up by liver cells via receptor-mediated endocytosis; major carrier of cholesterol in blood; regulates de novo cholesterol synthesis at level of target cell  high-density lipoproteins - contain endogenous cholesterol esters released from dying cells and membranes undergoing turnover

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