Fat Metabolism PDF

FAT METABOLISM The skinny on fat – a huge amount of stored energy... Sian Patterson, Ph.D. Associate Professor, Teaching Stream  This or That? mu Epinephrine O Insulin Both storeglycogen Muscle O...

FAT METABOLISM The skinny on fat – a huge amount of stored energy... Sian Patterson, Ph.D. Associate Professor, Teaching Stream  This or That? mu Epinephrine O Insulin Both storeglycogen Muscle O Liver buses ↳ shares glucos glycogen glucose from glycogen Carbohydrates O Fats 2  Learning Objectives By the end of this lecture, students should be able to: Describe why, when and where fats are made and broken down. Review how much ATP is made from the reduced coenzymes produced in beta oxidation via oxidative phosphorylation. Describe the role of ACC and FAS for fat synthesis. Compare lipid synthesis to lipolysis (β oxidation). Contrast the reciprocal regulation of fat metabolism. 3  Triacylglycerol (Triglyceride, TG) > for later - · Extra carbons are stored in Ester linkage very hydrophobic triacylglycerol molecules, 120 primarily in fat cells but - for energy break also in muscle and other tissues. Acyl chains are connected to a glycerol backbone via ester bonds. Fatty acyl chains are Back saturated to allow for close packing. Chains must be · * Saturated : no double bonds (thinks hydrolyzed off for use. 3 to store Cs for later 4  hydrophobic In fat cell binds outside Tamphipathic ↓ Fatty Acids Fat binds to glucagon receptors - mobilization Adenylyl + albumin>- transports bloodstream ⑰ binds to B-andergenic ~ Epinephrine and glucagon signal via ~ GPCRs to activate 3 lipases. Peripheral a released >(H20) Lipases hydrolyze ester - bonds to produce free activatel fatty acids (FFAs) and ↑ Monoacylglycerol glycerol. H20 Diacylglycerol FFAs are transported in hydrolyze : H2o “Hormone Triacylglycerol the blood via albumin for cellular use. Sensitive Lipase” (HSL) cithosphorylate 5  Fat Mobilization via GPCR signalling B-andergenic glucose signal glucagon receptor low , fat uses Epinephrine and glucagon bind to G-protein coupled receptors (GPCRs) on adipose cells (and other tissues). The signalling response involves the release of Gα-GTP, activation of adenylyl cyclase and cAMP production, leading to Protein Kinase A (PKA) activation. - PKA phosphorylates and activates triacylglycerol lipase, also enzyme known as hormone sensitive lipase (HSL). > soluble due or to - - TAGs are hydrolyzed to 3 fatty acids (+ glycerol) that are released in the blood and transported via albumin. 6 Fat Metabolism Overview H20 (liver tissues) , + albumin or B-oxidation NADH, FADH2 ATP 7 What’s the difference between Acyl CoA and Acetyl CoA? longerchain more specific ↓ M-S-COA Cls Hsc-S-COA h =more than 2 8  Fatty Acid Activation in the Cytoplasm to Acyl chains are trapped in the cell by the covalent addition of coenzyme A. bring into cell and trap to make phospholipid/esse for energy ligase Acyl CoA Synthetase catalyzes a reversible reaction uses ATP (→ AMP) to form the fatty acyl CoA molecule. Pyrophosphate (PPi) hydrolysis to 2 Pi is favourable and drives this reaction in the forward direction. more stable 2 - > Hro - & & Acyl CoA synthetase ↳ Eatings Reversible ↳ To Couple drive forward : PPi-2 Pi 9  more energy ATPeADP-sirs/mot -34ks/mo ATP → AMP is Energetically Inefficient 95% of the ATP is made in oxidative phosphorylation using ADP as a substrate. In order for ATP to be made from AMP, AMP must be converted to ADP by sacrificing aO 2nd ATP: site Adenylate kinase PT : To AMP to make I ATP Synthase AMP + ATP & O → - 2 ADP → 2 ATP - ∴ Fatty acid activation by CoA requires 2 ATP (1 for activation and 1 for the production of ADP) and 1 H2O to hydrolyze PPi. 10  B- oxidation Mitochondria Structure ADP, Pi pyruvate Acyl CoA Amino acids porins : impermeablei Porins 11  Acyl CoA and β-oxidation Acyl CoA is made in the cytoplasm, but β-oxidation occurs inside the matrix. Acyl CoA can pass through outer membrane into the intermembrane space via porins, but it cannot cross the inner membrane since there is no transport mechanism. CoA is too large and water soluble making it unable to cross membranes. What’s the point of making fatty acyl CoA outside the matrix if it is only used in the matrix? : Regulation ↳ fatty acids used in mb. ↳ compartmentalization 12  cytoplan Carnitine Shuttle internaare > - remove & The carnitine shuttle regulates what comes into the mitochondria. CATI Carnitine Acyltransferase I (CAT I) moves the acyl chain onto carnitine inner. mb from CoA. Acyl carnitine is translocated across the inner membrane in exchange for CATII carnitine. Carnitine Acyltransferase II (CAT II) moves the acyl chain back onto CoA. free 2 adds ↓ Acyl CoA can then be catabolized in & β-oxidation. 13  from fats cells come - needepinephrine/glucagon (signals) translocase issatura 8 work need acy + carnitine faster ↑ 14  # of C # of double bonds a no need to - know details 16:0 CoA Al - saturated - 3 Beta H2O + CoA Oxidation Acetyl CoA (2 carbons) NADH + FADH2 14:0 CoA - M ↳ reactions Beta H2O + CoA Oxidation repeat NADH + FADH2 12:0 CoA M - each round ↳ H20 + COA 3 H2O + CoA consumed Beta Oxidation X4 ↳ NADH + FADH; NADH + FADH2 produced 10:0 CoA => Repeat... the last round starts with 4:0 and produces 2 Acetyl CoAs 15 n rounds- let or 16  4 steps of β-oxidation Fatty acid oxidation occurs at the β-carbon (number 3 carbon in the fatty acid chain). redox 1. Acyl CoA dehydrogenase: produces FADH2 and creates a double bond in the fatty acid chain. 2. Hydratase: adds water across the double bond (β-OH). 3. Dehydrogenase: produces NADH and creates a keto group on the β carbon in the chain. 4. Thiolase: uses CoA to release acetyl CoA, producing a fatty acyl CoA chain with 2 fewer carbons. 17  Overall β-oxidation of 16:0 CoA in the mitochondria 16:0 CoA + 7 NAD+ + 7 FAD + 7 H2O + 7 CoA = g acetyl CoA + 7 NADH + 7 FADH 2 + 7 H+ 18  Calculate the number of ATPs and H2O made by the complete 16 = oxidation of 16:0 CoA. Acetyl CoA ATP GTP NADH FADH2 H2O Beta Oxidation S - ss] 7-7 Citric Acid Cycle 8 - 824 8-16 ETC -31 15 46 77 5722 5.. ATP Synthase 100 lop Total los L 19  Calculate the number of ATPs and H2O made by the complete oxidation of 16:0 CoA. Y ( ) B-oxid : matrix  CARBOHYDRATES GLYCOGEN LIPIDS GLYCEROL GLUCOSE broke down FATTY ACIDS ENERGY GNG Glycolysis ATP make CO2 PYRUVATE LACTATE PROTEINS Beta Oxidation AMINO ACIDS ACETYL-COA KETONE BODIES Y & CHOLESTEROL amphibolic intermediate ↳ many pathways Citric Urea Acid Cycle Cycle Oxidative Phosphorylation NH3 CO2 ATP 26  Low Carb Diets What is the biochemical basis of low carb diets? What are the potential side effects? 27  Anabolic : fat synthesis Hormonal Response and Fat Synthesis As glucose levels rise, insulin signals for glucose uptake and catabolism in glycolysis. Fats and amino acids will also be imported for use in the cell. As ATP levels rise, glycolysis slows down and excess glucose is store as glycogen in muscle and liver cells. As ATP and NADH levels rise in the mitochondria, the citric acid cycle slows down, allowing for the synthesis of fat from Acetyl CoA. Excess macromolecules (carbs/fats/pr) will be first broken down to smaller precursors and energy that can be used to make fats, but Acetyl CoA is made in the mitochondria…. have to get it out of mit.. 28  Steps in Fatty Acid Synthesis Fatty Acid Processing Steps: 1. Export of mitochondrial Acetyl CoA to the cytoplasm for fat synthesis. from excess sugars/protein etc , -add W2 2. Carboxylation of acetyl CoA to malonyl CoA by Acetyl CoA Carboxylase (ACC). 3. Use of malonyl CoA to form 16:0 fatty acid chains by Fatty Acid Synthase (FAS). 29  Step 1 - Import & Export Differ Glycolysis Acetyl CoA Fat synthesis Cytoplasm or intermembrane space Acyl- carnitine Pyruvate Citrate- > exports s from acctyl CoA I Inner mitochondrial membrane Matrix carnitine Acyl-CoA Pyruvate A Citrate PDC β-oxidation cri Citric Acid Amino Acids ATP Acetyl CoA Cycle ATP 30  Step 1. Acetyl CoA is exported as Citrate COA Recall Coenzyme A cannot cross the inner mitochondrial membrane. Citrate synthase makes citrate in the Citric Acid Cycle, which can cross the inner membrane. Citrate is broken down by different enzymes to recreate acetyl CoA, regenerating a pyruvate molecule. costoplasm The pyruvate can then return to the mitochondria while Acetyl CoA is used for the synthesis of fatty acyl chains in the cytoplasm. 31 Fatty Acid Synthesis is an Anabolic Process Acyl chain synthesis occurs in the cytoplasm. 2 enzymes are needed – Acetyl CoA Carboxylase and Fatty Acid Synthase. Acetyl CoA Carboxylase converts Acetyl CoA to malonyl CoA, an activated 2-carbon carrying precursor for fatty acid synthesis. Acetyl CoA Carboxylase is the committed and regulated step for fatty acid synthesis. Acetyl CoA Carboxylase uses ATP, while Fatty Acid Synthase uses NADPH as reducing power. ↳ for anabolic 32  Step 2: Acetyl CoA Carboxylase (ACC) Acetyl CoA is carboxylated using ATP to produce Malonyl CoA. The presence of the CO2 group on malonyl CoA will be used to drive fatty acid synthesis by fatty acid synthase (step 3). Bicarbonate Coz t ATP 33  Malonyle Reciprocal Regulation for Fats When fat synthesis is ON, fat 7 degradation is OFF. This prevents the futile cycle of X synthesizing chains, then breaking them down. The product of Acetyl CoA Carboxylase (ACC) - malonyl CoA, inhibits CATI and shuts down the carnitine shuttle for the import of chains. ACC is also regulated for fat metabolism… 34  covalent modification > - ACC Regulation via Phosphorylation ↳similar mechanism like PDC ↳ male 35  What is the link between exercise and the inhibition of fat synthesis by: Epinephrine - GPCR activated fet synthesis Protein kinase A: inhibits Actyl COA Carboxylase : turn off when excessizing Exareise ↓At pp AMP-dependent kinase: ATP- > ADD-Amp C I Phosphorylate ACC : no fat synthesis 36  What is the link between exercise and the inhibition of fat synthesis by: Epinephrine - GPCR activated fet synthesis Protein kinase A: inhibits Actyl COA Carboxylase : turn off when excessizing worl Exareise fats f At app AMP-dependent kinase: ATP- > ADD-Amp C I Phosphorylate ACC : no fat synthesis 36  Regulation of Fat Metabolism Acetyl CoA Carboxylase is the committed step for FA synthesis. ACC is inhibited by phosphorylation with rising glucagon/epinephrine and AMP. Insulin and protein phosphatase activate ACC via dephosphorylation. product of fat synthesis -cutoplasm I Citrate can also stimulate ACC, while palmitoyl CoA (16:0 CoA) inhibits active ACC. The product, malonyl CoA also shuts down fat breakdown by inhibiting Carnitine Acyltransferase 1 (don’t forget your competing pathways!). 37  Step 3: Use of malonyl CoA to form fatty acid chains by Fatty Acid Synthase (FAS). very big cofactor using - · > - Carnitine enzyme similar O "C-CH (ACP) ↳ from ActCo The Acyl Carrier Protein (ACP) moves the intermediates between the different reaction sites. 38  Acetylt to carrier protein / release ACP = acyl carrier Fatty Acid Synthase (FAS) protein in FAS &Ac Step 1 - A condensation reaction (KS) KS Release CO2 - occurs with the release of CO2, - ↓ ul producing a chain that is 2 carbons generate w longer. energy H + + KR Step 2 - redox reaction requiring NADPH (KR). Step 3 – dehydration and H2O is DH released (DH). Step 4 – 2nd redox reaction using NADPH producing a saturated chain + H + ER (ER). saturated Repeat - 2 carbons from another → Repeat with malonyl CoA can then be used for the another Malonyl next round of reactions. CoA 39  Too long To Read makes maryroup Fat Synthesis I The synthesis of fatty acids requires the actions of both Acetyl CoA carboxylase (ACC) and Fatty Acid Synthase (FAS).Buses maynoyl + Acetyl inFound 7 cycles of FAS are required to generate 16:0. This involves 1 acetyl CoA and 1 malonyl CoA in the first cycle, followed by 6 malonyl CoA molecules for the next 6 rounds of reactions. Lots of energy is required for this anabolic pathway to proceed (ACC needs 7 ATPs to make 7 malonyl CoAs, and FAS needs 14 NADPHs). 2 per round Elongation of the 16:0 chain (18, 20, 22, 24) occurs in the ER, also using malonyl CoA and NADPH. Desaturases can introduce cis bonds, also requiring NADPH and oxygen. 40  Beta Oxidation Fatty Acid Synthase vs. Beta Oxidation FAS Beta Oxidation Location Cytoplasm Mitochondria Metabolic pathway Anabolic Catabolic Acetyl CoA, 2 Carbon Unit Malonyl CoA Acetyl CoA Coenzymes NADPH NAD+, FAD Enzymes involved 1 protein enzyme 4 separate enzymes β-OH intermediate D L # of rounds? z+ E - 1 41  Low Carb Diets What is the biochemical basis of low carb diets? Scarbs L private Acetyl COATOAA Accema lon scitrate - to Is Weight loss = glyrogen (fatbreakdown (hormone) What are the potential side effects? ↓ pyruvate NOAA 42  Key Messages Excess carbons from fats, carbohydrates and proteins are stored as triacylglycerol molecules. GPCR signalling is required for TAG breakdown, with fatty acids traveling in blood stream bound to serum albumin. Fatty acids are activated by acyl CoA synthetase, then imported into the mitochondria by the carnitine shuttle for breakdown in β oxidation. A blend of fuels and O2 are required to produce the maximum ATP output from fatty acyl chains. Fatty acid synthesis begins after Acetyl CoA is exported from mitochondria as citrate. Acetyl CoA Carboxylase (ACC) is the regulated step in fat synthesis. Fatty Acid Synthase (FAS) and beta oxidation have similar but reverse mechanisms and differ in many ways. 43