Lipids Part 4 - Lipogenesis and Beta Oxidation - PDF

Lipids Part 4 Lipogenesis and beta oxidation continued Dr. Heisel BMS100 Objectives – Lipolysis prereading List two uses of TG’s in liver Outline the process of lipolysis, including tissues involved, substrate, enzymes and products Discuss the purpose(s) of lipolysis in adipose and liver Describe th...

Lipids Part 4 Lipogenesis and beta oxidation continued Dr. Heisel BMS100 Objectives – Lipolysis prereading List two uses of TG’s in liver Outline the process of lipolysis, including tissues involved, substrate, enzymes and products Discuss the purpose(s) of lipolysis in adipose and liver Describe the regulation of lipolysis by glucagon, epinephrine and insulin Objectives – beta oxidation Outline the process of beta oxidation of fatty acids with even number of C, including: Starting substrate, enzyme names, energy intermediates produced, final products and where they go next wrt energy production Determine the difference in energy production of unsaturated and/or odd numbered fatty acids when compared with saturated, even numbered chains Describe, with rationale, what is happening to the levels of the following in MCAD deficiency Glucose, fatty acids, ketones Outline the general purpose of peroxisomal beta ox, and how it contrasts to mitochondrial beta ox Beta oxidation O β II H3C – CH2 – CH2 – C - OH Prelearning review: beta ox of saturated, evennumbered fatty acids Each round produces: 1 FADH2 (from B2) and 1 NADH (from B3) Overall, one less than half the number of C’s Acetyl CoA Overall, equal number to half the number of C’s Dehydrogenase Hydratase Dehydrogenase Thiolase β Beta Oxidation What about unsaturated and/or odd-numbered fatty acid chains? Beta oxidation: Unsaturated H HHO R-C -C-C-C-SCoA HH H HHO R-C=C-C-C-SCoA H H H HO FAD FADH2 H HO R-C-C =C-C-SCoA HH R-C-C =C-C-SCoA HH Enzymes names for saturated vs unsaturated? For each double bond, how many fewer ATP produced? Beta oxidation: Odd-numbered Last round of beta ox produces 1 acetyl CoA and 1 propionyl CoA C–C–C–C–C–C–C–C–C Acetyl CoA Acetyl CoA 1st round 2nd round Acetyl CoA Propionyl CoA Last round Propionyl CoA uses up 1 ATP to enter CAC Enters at succinyl CoA step, by-passing the production of 2 NADH * How many ATP less does a propionyl CoA make compared to an acetyl CoA? * Beta Oxidation: Odd-numbered Creation of 2 NADH is missed Proprionyl CoA ATP Beta ox: Check your knowledge at home You should be able to answer both of these questions without calculating the full energy yield of each fatty acid How much less energy do you get after the full beta ox of a 16:2 fatty acid vs a 16:0 fatty acid? Provide a brief justification. Which provides more energy after beta ox: a 17:0 or a 16:0 fatty acid? How much less, and why? Answer slide can be found at the end of the presentation Beta Oxidation MCAD deficiency Deficiency of the first enzyme of beta oxidation (medium chain acyl dehydrogenase) Class poll: next slide Dehydrogenase β Beta Oxidation Which three of the following will result from an MCAD deficiency? Why? A High concentration of fatty acids B Low concentration of fatty acids C Hyperglycemia D Hypoglycemia E Hyperketonuria F Hypoketonuria Beta oxidation MCAD deficiency: What is happening with GNG? Low oxaloacetate, so less GNG Why low oxaloacetate? Used up: Combines with acetyl CoA to enter CAC to make energy Production decreased: Acetyl CoA levels low - Used for energy in CAC - Less production via beta ox With low acetyl CoA, cannot activate which reaction to make oxaloacetate? Beta oxidation MCAD deficiency Can lead to coma and death if untreated, but once identified can be successfully treated with diet Identified by newborn screening Diet: Frequent feeding Infants present as very lethargic, may need to wake for feedings Diet high in carbs and protein, low in fat Beta oxidation Peroxisomal beta oxidation Used to shorten very long chain fatty acids (VLCFA’s) into medium and long chain fatty acids No carnitine transport required A transport protein brings the fatty acyl CoA’s across the single membrane The shortened fatty acids are then further degraded in the mitochondria as per usual Major difference to mitochondrial beta oxidation: does not result in energy production Remember: ETC is only in mitochondria Citric Acid Cycle Part 2 CAC continued Dr. Heisel BMS100 Objectives Outline which three types of molecules can be catabolized to feed into CAC Provide specific entry points for alanine, aspartate, glutamate Outline the substrate(s), enzyme, product(s) for the conversion of pyruvate to acetyl CoA List the coenzymes involved in the PDH complex and briefly outline their roles List the overall reaction products of CAC For each individual step, provide substrate(s), enzyme, product(s) Determine the energy yield from one round of CAC Identify the major regulatory enzymes of CAC and their inhibitors/activators Citric Acid Cycle: Entry points Review: Glucose, fatty acids and amino acids can all feed into CAC Glucose Ala*, Cys, Gly, Ser, Thr, Trp Fatty acids Pyruvate Acetyl CoA Oxaloacetate Leu, Phe, Tyr, Trp, Lys, Thr, Ile Asp*, Asn Fumarate CAC Asp*, Phe, Tyr Succinyl CoA Ile, Met, Val Citrate α-ketoglutarate Arg, Gln, His, Pro, Glu* 17 Citric Acid Cycle Review – Overall products are: 3 NADH 1 FADH2 1 ATP via GTP 2 CO2 1 3 1 1 2 1 2 CAC – Prep Step Review: Pyruvate dehydrogenase complex allows pyruvate from glycolysis to enter CAC via acetyl CoA Involves: 3 enzymes: E1, E2, E3 FYI only: pyruvate dehydrogenase, dihydrolipoyl transacetylase, dihydrolipoyl dehydrogenase 4 coenzymes: TPP (from B1), CoA (from B5), lipoamide (lipid coenzyme), NAD+ (from B3), FAD (from B2) C=O CH3 CAC – PDH Complex E1 uses TPP (from B1) to pick up the acetyl group This releases CO2 E2 uses lipoamide to transfer the acetyl group from TPP to CoA (from B5) This reduces the lipoamide and creates acetyl CoA What’s left for E3? Resetting the coenzymes to reuse. FAD resets lipoamide, becoming FADH2 NAD+ resets FADH2 back to FAD, becoming NADH What resets the NADH back to NAD+? C=O CH3 Citric Acid Cycle Glycolysis prep step Pyruvate dehydrogenase complex Step one – creation of citrate See prereading Enzyme = citrate synthase Citric Acid Cycle Step two Enzyme = aconitase AKA aconitate hydratase Reaction involves an aconitate intermediate Citrate Aconitate Isocitrate Endergonic: what drives the reaction forward? Citric Acid Cycle Step three Enzyme = ? Exergonic reaction Helps pull previous reaction forward Produces NADH and CO2 Citric Acid Cycle Step four Enzyme = alpha ketoglutarate dehydrogenase (complex) Exergonic reaction Produces NADH and CO2 What other reaction is similar? Citric Acid Cycle Step five Enzyme = succinyl CoA synthetase Thioester bond broken, energy released Used to make what? This step involves “substrate-level phosphorylation” – what does this mean? Citric Acid Cycle Step six *Enzyme = ? FADH2 produced *Unlike the other enzymes, this one is attached to the inner mitochondrial membrane. It also serves as part of the ETC and is the entry point for FADH2 from CAC into ETC. Citric Acid Cycle Step seven Enzyme = fumarase aka ? Water is added across the db Citric Acid Cycle Step eight Enzyme = ? NADH generated Endergonic rxn – what drives it forward? Citric Acid Cycle Summary First half (following glycolysis) Start with 3 C pyruvate How many pyruvate can enter CAC after one round of glycolysis? For each pyruvate, how many C’s enter the CAC? What do they enter as? Also made by beta ox and some amino acid catabolism What happens to the rest of the carbons from pyruvate? Energy Yield: 2 NADH and 1 GTP (ATP) Second half Conversion of succinate to oxaloacetate Energy Yield: 1 NADH and 1 FADH2 Cycle goes back to beginning: oxaloacetate + acetyl CoA to make citrate Citric Acid Cycle Regulation Regulation happens at highly exergonic and irreversible steps 1= PDH complex 1 Inhibited by: Acetyl CoA, NADH 2 4 Product inhibition 3 ATP Indicates high energy Citric Acid Cycle Regulation 1= PDH complex 1 Activated by: CoA, NAD+ Substrate activation AMP Indicates low energy Ca+2 2 4 3 Released during muscle contraction, signifies need for more energy Citric Acid Cycle Regulation 2= citrate synthase 1 Inhibited by: Citrate Product inhibition NADH, ATP Products of CAC, indicate high energy 2 4 Succinyl CoA 3 Product of CAC, used to make energy (GTP) Citric Acid Cycle Regulation Take home question Using the previous slides, justify the following on your own: 1 3= isocitrate dehydrogenase Activated by: ADP, NAD+, Ca+2 Inhibited by: 2 4 3 NADH, ATP 4 = alpha ketoglutarate dehydrogenase Activated by: Ca+2 Inhibited by: Succinyl CoA, NADH, ATP, GTP Ketones Ketogenesis and ketolysis Dr. Heisel BMS100 Objectives Outline the process and purpose of ketogenesis and ketolysis Describe the interplay between metabolic pathways that can lead to ketogenesis Describe how starvation, Atkin’s diet and uncontrolled type 1 diabetes mellitus can lead to ketogenesis Discuss signs and symptoms of uncontrolled DM Ketogenesis If we have excess acetyl CoA, what can the liver do with it? Store it as ketone bodies for other tissues to use (ketogenesis) Brain, heart, skeletal muscle can break down ketone bodies (ketolysis) when needed for energy Acetyl CoA -> Ketone Bodies Ketone Bodies -> Acetyl CoA Ketogenesis (Liver) 1,2 3 3 acetyl CoA make HMG-CoA Can be diverted to synthesis of? Ketone bodies: Can be used by other tissues for energy Ketone body: Expired Ketolysis (Extra-hepatic) Liver lacks enzyme that converts acetoacetate to acetoacetyl CoA Therefore liver does not use the ketone bodies that it makes Acetoacetyl CoA 2 acetyl CoA To CAC Ketones When would your liver use acetyl CoA for ketogenesis as opposed to CAC? In times of low blood sugar For example, during starvation or when following the Atkins (high protein, low carb) diet, the liver makes ketones to send out to other tissues Class Poll Which two of the following would apply in the liver when blood sugar is low? A – Beta oxidation is decreased B – Beta oxidation is increased C – Gluconeogenesis is decreased D – Gluconeogenesis is increased Ketones Diagram the connection between low blood sugar and formation of ketone bodies in the liver Ketones Uncontrolled type 1 diabetes mellitus (DM) can cause build up of ketone bodies Type 1 DM: autoimmune condition where insulinsecreting beta cells of pancreas are damaged/destroyed Results in low insulin and high blood sugar levels If ketogenesis normally results from low blood sugar, why does it happen with high blood sugar in uncontrolled DM?!? Ketones The interplay between insulin and glucagon in DM is what leads to ketogenesis Normally, insulin is released when blood sugar is high In DM, insulin is low despite hyperglycemia Remember, beta cells are damaged Glucagon levels are inversely related to insulin levels When insulin is high, glucagon is low When insulin is low, glucagon is high This is the case in DM Ketones In DM, we have: Hyperglycemia with high glucagon What does glucagon do to glycolysis? What does this in turn do to beta ox? What does glucagon do to GNG? What does this in turn do to CAC? (At home: review regulation of glycolysis/GNG by insulin and glucagon, including the role of F-2,6-bis P) Add to your diagram to show how uncontrolled DM can also result in ketogenesis Ketones Ketosis High levels of ketones Not usually a problem Ketone bodies are used, expired, or excreted in the urine Excretion of ketones used as a measure of Atkin’s diet Diabetic ketoacidosis Defined by high levels of ketones combined with low blood pH and hyperglycemia Seen in uncontrolled diabetes mellitus Ketones Diabetic ketoacidosis continued Low blood pH = acidosis: from build up of ketone bodies Hyperglycemia: from low insulin, high glucagon Leads to diuresis: increased urination from osmotic pull of glucose Leads to electrolyte imbalances, as ions are excreted due to excessive urination Untreated, can lead to coma and death Ketones If a patient comes to you in the initial stages of diabetic ketoacidosis: What warning sign might you be able to detect while they are in your office with you? What complaint might they have that is related to the hyperglycemia? End of lecture Beta ox answer slide to follow Beta Ox Answer Slide 16:2 Each db means one less FADH2 Each FADH2 can make 2 ATP via electron transport 2 FADH2 * 2 ATP each = 4 ATP less 17:0 vs 16:0 Both have same number of cycles Same number of FADH2 and NADH 16:0 = 8 acetyl CoA 17:0 = 7 acetyl CoA and 1 propionyl CoA Only need to consider which makes more energy, 1 acetyl CoA or 1 propionyl CoA Propionyl CoA makes 7 ATP less than acetyl CoA 1 ATP used to enter CAC 2 NADH less generated, = 6 ATP 7 ATP less for 17:0