BMM339 Exam 3 PDF

Triacylglycerol Synthesis (Lipogenesis) - Triacylglycerols are synthesized for storage - For triacylglycerol synthesis, glycerol-3-phosphate or dihydroxyacetone phosphate reacts sequentially with 3 molecules of Acyl-CoA Acyl-CoA molecules are fatty acid esters of CoASH Glyceroneogenesis - Gly...

Triacylglycerol Synthesis (Lipogenesis) - Triacylglycerols are synthesized for storage - For triacylglycerol synthesis, glycerol-3-phosphate or dihydroxyacetone phosphate reacts sequentially with 3 molecules of Acyl-CoA Acyl-CoA molecules are fatty acid esters of CoASH Glyceroneogenesis - Glyceroneogenesis: synthesis of Glycerol-3-PO4 from substrates other than glucose or glycerol Malate is the primary substrate for glyceroneogenesis Lipolysis - Lipolysis: metabolic process that degrades triacylglycerols into free fatty acids and glycerol Occurs in adipose tissue during fasting, vigorous exercise and in response to stress Occurs when energy reserves are low Fatty acid binding proteins transport the fatty acids via blood to various tissues Fat Metabolism - Triglycerides are hydrolyzed to fatty acids and glycerol in adipocytes Fatty acids diffuse from adipocyte into blood stream In blood, the fatty acid binds with albumin and transported into other tissues Fatty acids are preferred energy source for heart, skeletal muscle and liver Brain and RBC cannot use fatty acids for energy Fatty acids are cotransported with Na+ into cells (i.e. Na+ fatty acid cotransport) Activation of Fatty Acids - Fatty Acid Activation: Acyl-CoA formation Enzyme Acyl-CoA synthetase converts the fatty acids into Acyl-CoA (activated fatty acids) in the presence of ATP and Coenzyme-A (CoASH) Acyl-CoA formation happens at the outer mitochondrial membrane Acyl-CoA formation in Mitochondria Formation of Acylcarnitine - Acyl-CoA rxts with carnitine to form acylcarnitine Carnitine is an acyl group carrier molecule Formation of acylcarnitine is catalyzed by acyl transferase-1 (CAT-1) enzyme Fatty Acid Transport into Mitochondria - Carnitine-mediated transfer of acyl groups is accomplished through the following mechanism: 1.) Acyl-CoA converted into acylcarnitine 2.) Carrier Protein transfers acylcarnitine into matrix 3.) Acyl-CoA regenerated 4.) Carnitine recycled to intermembrane space Lecture 28: Fatty Acid Oxidation and Regulation Fatty Acid Transport into Mitochondria 1.) Fatty acids from blood are co-transported into cells by Na+-fatty acid cotransporter 2.) Acyl-CoA synthase converts the FA’s into Acyl-CoA Facilitates transport across the mitochondrial outer membrane into intermembrane space 3.) Acyl-CoA converted into Acyl-carnitine by Carnitine acyltransferase-1 (CAT-1) present in mitochondrial outer membrane 4.) Acyl-Carnitine transported into mitochondrial matrix by carnitine-Acylcarnitine exchanger 5.) Carrier protein transfers acylcarnitine into mitochondrial matrix 6.) Carnitine acyltransferase-2 (CAT-2) present in inner membrane activates the acylcarnitine into Acyl-CoA 7.) Acyl-CoA is ready for Beta-oxidation Beta-Oxidation of Saturated Fatty Acids - Beta Oxidation: series of 4 reaction in the fatty acid oxidation Each beta-oxidation cycle: 2 - carbon fragment is removed as acetyl-coa ^Acetyl Coa molecules produced are used in the citric acid cycle Beta-Oxidation (Reactions #1 and #2) -Step 1: Acetyl CoA → trans-𝛼,𝛽-Enoyl-CoA Enzyme: Acyl-CoA dehydrogenase -Step 2: trans-𝛼,𝛽-Enoyl-CoA → 𝛽-Hydroxyacyl-CoA Enzyme: Enoyl-CoA hydrase Beta Oxidation (Reactions #3 and #4) -Step 3: 𝛽-Hydroxyacyl-CoA → 𝛽-Ketoacyl-CoA Enzyme: L-𝛽-Hydroxyacyl-CoA -Step 4: 𝛽-Ketoacyl-CoA → Acyl-CoA + Acyl-CoA Enzyme: 𝛽-Ketoacyl-CoA thiolase Complete Oxidation of Fatty Acid - Aerobic oxidation of a fatty acid generates a large number of ATP Molecules Yield of ATP from oxidation of Palmitoyl-CoA = 108 ATP (106 total) ATP production per each carbon in: Fatty Acid: 6.6 ATP/Carbon Glucose: 5.5 ATP/Carbon Complete oxidation of Palmitic Acid Oxidation of Unsaturated Fatty Acid (Oleic Acid) -Oxidation of Double Bonds Because of the cis double bond, 1 additional enzyme/reaction is required to degrade these molecules Enoyl-CoA isomerase Oxidation of Odd-Chain Fatty Acid (Propionyl-CoA formation) - The last 𝛽-oxidation cycle of the odd chain fatty acids yields one acetyl-CoA and one propionyl-CoA Oxidation of Odd-Chain Fatty Acid (Propionyl-CoA → Succinyl-CoA) - Last 𝛽-oxidation cycle of an odd chain fatty acids yields one acetyl-CoA and one propionyl-CoA Propionyl-CoA is then converted to succinyl-CoA, a citric acid intermediate Oxidation of Branched Chain Fatty Acid (𝛼-oxidation) - 𝛼-Oxidation: mechanism for degrading branched chain fatty acids (e.g. Phytanic Acid) Phytol (Green veggies) is converted to phytanic acid and is oxidized in peroxisomes in humans After activation to a CoA derivative, the product pristanic acid can be degraded by 𝛽-oxidation Oxidation of Branched Chain Fatty Acid 𝛽-Oxidation in Peroxisomes -Peroxisomal 𝛽-Oxidation: shorten very long chain fatty acids [e.g. tetracosanoic (24:0) and hexacosanoic acids (26:0)] into medium chain fatty acids Halts at octanoyl-CoA -𝛽-Oxidation does not generate ATP Medium-chain fatty acids produced by 𝛽-oxidation are further oxidized/degraded in the mitochondria The initial reaction produces H2O2, which can be dealt with by peroxisomal catalase to form H2O 𝛽-Oxidation in Peroxisome vs. Mitochondria Ketogenesis and Ketone Bodies - Ketogenesis: production of ketone bodies Ketone bodies include acetoacetate, Beta-Hydroxybutyrate and acetone Ketone bodies are produced from excess acetyl-CoA Most of the acetyl-CoA produced during Beta-oxidation is used in the citric acid cycle Under normal condition, only small amount of excess acetyl-CoA produced Ketosis -Ketosis: process that produces acetone Acetoacetate spontaneously decarboxylated to form acetone Ketosis heavily occurs during extended starvation and uncontrolled diabetes Ketone Body Formation 1.) 2 acetyl-Coa condensed to form acetoacetyl-CoA 2.) Acetoacetyl-CoA condensed with another acetyl-CoA to form HMG-CoA 3.) HMG-CoA lyase hydrolyses HMG-CoA into acetoacetate 4.) Acetoacetate spontaneously decarboxylated to form acetone Acetoacetate also can be reversibly reduced to Beta-Hydroxybutyrate Heart and skeletal muscle use ketone bodies for energy Brain uses ketone bodies as energy source during prolonged starvation Conversion of Ketone bodies to Acetyl-CoA - Ketone bodies can also be converted back into acetyl-CoA Beta-Hydroxybutyrate to acetyl-coa formation occurs in the mitochondrial matrix of liver Lecture 29: Fatty Acid Synthesis and Regulation Fatty Acid Biosynthesis -Fatty acid synthesis takes place in the cytoplasm -Intermediates are covalently linked to acyl carrier protein (ACP) ACP is a fatty acid activator in fatty acid biosynthesis (Recall that CoA is used as an activator for Beta-Oxidation) Acetyl-CoA + CO2 → Malonyl-CoA Acetyl-CoA and Malonyl-CoA are activated as Acetyl-ACP and Malonyl-ACP for fatty acid synthesis -Four Step Repeating Cycle (Extension by 2 carbons/cycle) Condensation Reduction Dehydration Reduction Fatty Acid Synthesis -Fatty acid Synthase: Enzyme of fatty acid synthesis are packaged together in this complex -Only fatty acid synthesized by mammal is palmitic acid (16:0) Longer and shorter fatty acids, and unsaturated fatty acids are synthesized by palmitic acid - 2 Carbons are added at a time during FA synthesis Fatty acid synthesis begins from the methyl end and proceeds towards the carboxyl end Fatty Acid Synthase (FAS) -Fatty acid Synthase is a multi-enzyme complex of distinct enzyme activities: Malonyl-Acyl Transferase (MAT) Ketosynthase (KS) Keto Reductase (KR) Dehydratase (DH) Enoyl Reductase (ER -FAS is a X–shaped homodimer of 2 polypeptides Each polypeptide contains 7 catalytic domain and ACP Synthesizes 2 fatty acids simultaneously Fatty Acid Biosynthesis -Fatty Acid Biosynthesis occurs in 2 phases: Phase 1: Synthesis of Malonyl-CoA Phase 2: Sequential addition of 2 carbon units to synthesize palmitic acid (16:0) -Substrates for fatty acid biosynthesis are Acetyl-ACP and Malonyl-ACP Acetyl-CoA rxts with ACP-SH (acyl carrier protein) to for Acetyl-ACP Malonyl-CoA rxts with ACP-SH (acyl carrier protein) to form Malonyl-ACP Fatty Acid Synthesis (Phase 1: Malonyl-CoA formation) - Acetyl-CoA Carboxylase (ACC1): carboxylates the acetyl-CoA to synthesize Malonyl-CoA Irreversible rxn Rate-Limiting step in fatty acid biosynthesis -Malonyl-CoA is activated by Malonyl-Acetyl transferase to Malonyl-ACP ACP: fatty acid activator in biosynthesis Acetyl-ACP Formation -Acetyl-CoA rxts with ACP-SH to form Acetyl-ACP (activated acetate) Acetyl-ACP is transferred to Ketosynthase (KS) unit of fatty acid synthase complex Fatty Acid Biosynthesis (Phase 2) 1.) FA synthesis begins with a condensation rxn 2.)Acetyl group is transferred to Malonyl group to form Acetoacetyl-ACP, Catalyzed by KS 3.) Reduction of Beta-carbonyl group, forms an alcohol Catalyzed by Beta-Ketoacyl-ACP reductase (KR) 4.) Removal of water to form carbon-carbon double bond is catalyzed by Beta-hydroxyacyl-ACP dehydratase 5.) Reduction by Enoyl-ACP reductase (ER) yields a saturated 4 carbon acyl group 6.)The acyl group is then transferred from ACP to SH group of Beta-Ketoacyl synthase (KS) to begin new elongation 7.) The acyl chain lengthens by 2 carbons, as it condenses with another ACP-linked Malonly group 8.) FA synthesis ends with the release of palmitate from ACP by thioesterase (TE) Repeated Cycles for Elongation - 1st Cycle Result: 4-carbon chain associated to the ACP arm The 4 carbon chain gets transferred back to the KS arm A new malonyl-CoA is introduced on the ACP arm - The rxns proceed as before. For each cycle, the acyl group is transferred to the 𝛼-carbon of Malonyl-CoA and is 2 carbons longers than the previous cycle -At the end of 7 cycles, a fatty acid with 16 carbon is attached to the ACP arm (Palmitoyl-ACP) The C16 unit is hydrolyzed from ACP to yield free palmitate Net Rxn: 8 acetyl-coa +14 NADPH + 17 H + 7 ATP → Palmitate +14 NADP + 7ADP + 7 Pi + 8 CoASH + 6 H2) Acetyl-CoA Carboxylase (ACC) - Acetyl-CoA Carboxylase (ACC1): key enzyme is FA synthesis Catalyzes the rate limiting step in FA Synthesis -ACC exist in active form and inactive forms: Active form: Polymerized-Dephosphorylated (Dimer) Inactive Form: Phosphorylated Monomer Allosteric Regulation of ACC1 -Activator: Citrate: a feedforward activator promotes polymerization of ACC1 -Inhibitor: Palmitoyl-CoA: the end product of FA synthesis depolymerizes to inhibit ACC1 Hormonal Regulation of ACC1 -Insulin: Dephosphorylates and activates ACC1 -Epinephrine and Glucagon: phosphorylates and inhibits ACC1 Fatty Acid Elongation and Desaturation -FA elongation and desaturation are a closely integrated process Both take place in the ER (important regulating membrane fluidity) -For FA Elongation and Desaturation: palmitic acid is first activated to Palmitoyl-CoA -For FA Elongation ONLY: 2 carbon unit is supplied by Malonyl-CoA Elongases: enzymes that synthesize longer chain fatty acids -Fatty acids CoA Desaturates: enzyme that synthesize unsaturated fatty acids Specific for specific position of double bond -Mammals lack the enzymes to introduce a double bond at carbon atoms beyond C9 FA containing double bonds beyond C9 are supplied by diet ← Essential FA (EFA) Desaturases are Specific positions of the double bond Similarity Between FA synthesis and Beta-Oxidation - Looks like FA synthesis is the reverse of Beta-Oxidation -FA synthesized by the sequential addition of 2-carbon group supplied by malonyl-CoA - Beta-oxidation removes 2-carbon group as acetyl-CoA Same intermediates: Beta-Ketoacyl (1), Beta-Hydroxyacyl (2), Alpha,Beta-unsaturated acyl (3) are found in both pathways Differences between FA synthesis and Beta-Oxidation 1.) Location: FA synthesis occurs in cytoplasm, Beta-oxidation occurs in mitochondria and peroxisome 2.) FA synthesis: consumes NADPH Beta-Oxidation: generates NADH and FADH2 3.) Enzymes used in FA synthesis and Beta-oxidation are different 4.) FA synthesis intermediates are linked to acyl carrier protein (ACP). while Beta-oxidation intermediates are attached to CoA Lecture 30: Phospholipids and Cholesterol Metabolism Phospholipids -2 Types of Phospholipids: Phosphoglycerides (Class-4) Sphingomyelin (Class-5) -Phosphatidylethanolamine (also called cephalin): stabilizes the membrane curvature constitutes 25% if all phospholipids in human -Phosphatidylcholine (PC): surfactant Major component of biological membranes -Phosphatidylserine (PS): acts as a signal for macrophages to engulf cells Important component of biological membrane syl Synthesis of PhosphatidylEthanolamine and PhosphatidylCholine 1.) Ethanolamine and choline enter the cell and phosphorylated by respective kinase 2.) Phospho-ethanolamine rxts with CTP to form CDP-ethanolamine 3.) Phosphocholine rxts with CTP to from CDP-Choline 4.) Diacylglycerol is synthesized from triacylglycerol 5.) CDP-ethanolamine and CDP-choline rxts with diacylglycerol to form phosphatidylethanolamine and phosphatidylcholine, respectively Phospholipid Turnover -Phospholipid Turnover is rapid Turnover: the replacement of fatty acid with new fatty acid - Phospholipids are degraded by phospholipases (PLA): PLA1: Hydrolyzes the ester bond of C1 of glycerol PLA2: Hydrolyzes the ester bond of C2 og glycerol PLB: Hydrolyzes both C1 and C2 ester bonds PLC: hydrolyzes the phosphodiester bond between glycerol and phosphate PLD: Hydrolyzes the phosphodiester bond between phosphate and fatty acid (e.g. R3) Synthesis of Sphingosine, Ceramide, Sphingomyelin, and Glycosphingolipids 1.) Sphingosine Synthesis: Palmitoyl-CoA condensed with AA, serine, to form Sphinganine Palmitoyl-CoA + Serine → Sphinganine 2.)Ceramide Synthesis: Sphinganine rxts with a long chain fatty acid to form ceramide Sphinganine + long chain fatty acid → Ceramide 3.)Sphingomyelin Synthesis: Ceramide rxts with phosphatidylcholine or phosphatidylethanolamine to form Sphingomyelin Ceramide + (phosphatidylcholine or phosphatidylethanolamine) → Sphingomyelin 3.)Galactocerebroside Synthesis: Ceramide rxts with UDP-galactose to form galactocerebroside Ceramide + UDP-Galactose → Galactocerebroside 3.)Glucocerebroside Synthesis: Ceramide rxts with UDP-glucose to form Glucocerebroside Ceramide + UDP-glucose → Glucocerebroside Sphingomyelin Metabolism -Sphingomyelin: the hydroxyl group of ceramide esterified to phosphate group of either phosphorylcholine of phosphorylethanolamine Sphingomyelin: insulates nerves and facilitates rapid transmission of nerve impulse Sphingomyelinase: degrades sphingomyelin Abnormal accumulation of sphingomyelin due to defective sphingomyelinase results in Niemann-Pick Syndrome Cerebrosides Metabolism -Monosaccharide is the head group in cerebrosides! -Glucocerebroside: Found in non-neuronal tissues 𝛽-Glucosidase degrades the glucocerebrosides Abnormal accumulation due to defective 𝛽-glucosidase results in Gaucher’s disease -Galactocerebroside: found in brain cell membrane 𝛽-galactosidase degrades the galactocerebrosides Abnormal accumulation due to defective 𝛽-galactosidase results in Krabbe’s disease Sulfatides: sulfated galactocerebrosides ^Arylsulfatase A degrades the sulfatide ^Sulfatide accumulation due to defective Arylsulfatase A resulting in Alzheimer’s and Parkinsons Ganglioside Metabolism