Bài giảng Basic Food Chemistry - Chapter 4: Metabolism of Tag

Nội dung text: Bài giảng Basic Food Chemistry - Chapter 4: Metabolism of Tag

1. Reactivity of Coenzyme A (HSCoA) Nucleophilic acyl substitution O O HY • • CH3CSCoA CH3C Y • + HSCoA Acetyl coenzyme A is a source of an acetyl group toward biological nucleophiles(it is an acetyl transfer agent)
2. Formation of Acetyl ACP and Malonyl ACP • The intermediates(acetyl-ACP and malonyl-ACP) in fatty acid synthesis are covalently linked to the acyl carrier protein (ACP)
3. Condensation and Reduction In reactions 1 and 2 of fatty acid synthesis: • Condensation by a synthase combines acetyl-ACP with malonyl-ACP to form acetoacetyl-ACP (4C) and CO2 (reaction 1) • Reduction converts a ketone to an alcohol using NADPH (reaction 2)
4. Lipogenesis Cycle Repeats Fatty acid synthesis continues: • Malonyl-ACP combines with the four-carbon butyryl- ACP to form a six-carbon- ACP. • The carbon chain lengthens by two carbons each cycle
5. Elongation and Unsaturation • Endoplasmic reticulum systems introduce double bonds into long chain acyl–CoA's – Reaction combines both NADH and the acyl– CoA's to reduce O2 to H2O • convert palmitoyl–CoA to other fatty acids – Reactions occur on the cytosolic face of the endoplasmic reticulum. – Malonyl–CoA is the donor in elongation reactions
6. The synthesis of TAG 1. Mono-acylglycerol pathway (MAG pathway) (for dietary fat digestion and absorption) CH OCOR CH2OCOR pancreatic 2 CH2OH lipase CHOCOR CHOCOR CHOCOR CH OH CH2OCOR 2 CH2OH TAG FA DAG MAG intestinal lumen FA FA ATP,CoA acyl CoA CH2OH CHOCOR CH2OH MAG intestinal epithelium lymphatic vessels Chylomicrons adipose tissue
7. Catabolism of TAG
8. ❑ A 4-carbon acid (oxaloacetate) is needed to react with excess acetyl-CoA and form citrate ❑ When OAA is not available, excess acetyl - CoA in liver are condensed to form ketone bodies ❑ OAA is limited during scarcity of glucose for glycolysis. In starvation and diabetes, glycogen is broken down. Fatty acids of fat depots are metabolized to supply ATP needs producing excess of the ketone bodies
9. Ketone Body Formation
10. Conversion of Ketone Bodies to Acetyl-CoA
11. Lipolysis – Diagrammatic View
12. Fatty Acid Formation • Shorter fatty acids undergo fewer cycles • Longer fatty acids are produced from palmitate using special enzymes • Unsaturated cis bonds are incorporated into a 10- carbon fatty acid that is elongated further • When blood glucose is high, insulin stimulates glycolysis and pyruvate oxidation to obtain acetyl CoA to form fatty acids
13. Sources of NADPH • The malate dehydrogenase and NADP+–linked malate enzyme reactions of the citrate shuttle exchange NADH for NADPH
14. Biosynthesis of glycerophospholipids 1. DAG shunt is the major pathway HO-CH2-CH-COOH for biosynthesis of phosphatidyl NH2 serine choline (lecithin) and phosphatidyl CO2 ethanolamine (cephalin) HO-CH2-CH2-NH2 3(S-adenosylmethionine) + ethanolamine HO-CH2-CH2-N(CH3)3 ATP choline kinase ATP ADP kinase ADP P -O-CH -CH -NH 2 2 2 + phosphoethanolamine P -O-CH2-CH2-N(CH3)3 CTP phosphocholine cytidyl transferase DAG PPi O H2C O C R1 CDP-O-CH2-CH2-NH2 O CDP-ethanolamine C R2 C O H CDP -O-CH2-CH2-N(CH3)3 CDP-choline H2C OH diacylglycerol transferase CMP phosphatidyl ethanolamine (PE) phosphatidyl choline (PC)
15. Degradation of glycerophospholipids O O H2C O C R1 H2C O C R1 O O R C O C H R C O C H 2 _ O 2 O O P OH H2C OH O P O X H2C _ XOH _ diglyceride O O phosphatidic acid H2O phospholipase C O phospholipase D H2C O C R1 O R C O C H glycerophospholipid 2 O H2C O P O X _ O phospholipase A1 phospholipase A2 H2C OH O O O O R C OH H C O C R R C O C H R1 C OH 2 2 1 2 O C H C O P O X HO H lysophospholipid 1 2 _ O O H C O P O X lysophospholipid 2 2 _ O O O R C OH phospholipase B 2 R1 C OH 2 phospholipase B H2C OH 1 HO C H O H2C O P O X _ O (glycerophophocholine)
16. Metabolism of cholesterol
17. Cholesterol Biosynthesis 2. processing of Squalene OH OH -O C-CH -C-CH CH OH - 2 2 2 2 2 Steps O2C-CH2-C-CH2CH2OPOP CH3 ATP CH3 Mevalonate 5-Pyrophospho mevalonate - CO2 - H2O CH3 Isomerase CH3-C=CH2CH2OPOP CH2=C-CH2CH2OPOP Dimethylallyl Isopentenyl CH pyrophosphate 3 pyrophosphate
18. 3. Conversion of Squalene to Cholesterol Squalene- Squalene 2,3-epoxide monooxygenase O2 O Squalene + 2,3-Oxidosqualene: H lanosterol cyclase CH3 CH3 CH 20 Steps 3 CH3 CH3 HO Lanosterol HO H3C CH3 Cholesterol
19. Lipoproteins biosynthesis
20. Metabolism of TAG (triacylglycerol) 1. Biosynthesis of TAG 2. Catabolism of TAG - Fatty acid beta oxidation -Ketogenesis and Ketone Bodies 3. Lipogenesis: Fatty Acid Synthesis 4. Some poly-unsaturated FA ramification