FA Biochem 8 Metabolism
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zingspeed27 on December 24, 2011
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26 terms
Chemistry | Math / Symbols |
|---|---|
 Glycolysis/ATP production How much ATP is produced via the different pathways? | Aerobic metabolism of glucose produces 32 ATP via malate-aspartate shuttle (heart and liver), 30 ATP via glycerol-3-phosphate shuttle (muscle) Anaerobic glycolysis produces only 2 net ATP per glucose molecule. ATP hydrolysis can be coupled to energetically unfavorable reactions. |
| Activated carriers (7) | Phosphoryl (ATP) Electrons (NADH, NADPH, FADH₂) Acyl (coenzyme A, lipoamide) CO₂ (biotin) 1-carbon units (tetrahydrofolates) CH₃ groups (SAM) Aldehydes (TPP) |
| Universal electron acceptors What are they, and what are they used for? | Nicotinamides (NAD⁺, NADP⁺) and flavin nucleotides (FAD⁺) NAD⁺ is generally used in CATABOLIC processes to carry reducing equivalents away as NADH. NADPH is used in ANABOLIC processes (steroid and fatty acid synthesis) as a supply of reducing equivalents. NADPH is a product of the HMP shunt. NADPH is used in: 1. Anabolic processes 2. Respiratory burst 3. P-450 4. Glutathione reductase |
| Hexokinase vs. glucokinase | Phosphorylation of glucose to yield glucose-6-phosphate serves as the 1st step of glycolysis (also serves as the first step of glycogen synthesis in the liver). Reaction is catalyzed by either hexokinase or glucokinase, depending on the location. |
| Hexokinase | Ubiquitous. High affinity (low Km), low capacity (low Vmax), uninduced by insulin. Feedback inhibited by glucose-6-phosphate Vmax represents the maximum rate achieved by the system Km is the substrate concentration at which the reaction rate is half of Vmax. |
| Glucokinase | Liver and β cells of pancreas. Low affinity (high Km), high capacity (high Vmax), induced by insulin. No direct feedback inhibition. Phosphorylates excess glucose (e.g. after a meal) to sequester it in the liver. Allows liver to serve as a blood glucose "buffer." "GLUcokinase is a GLUtton. It has high Vmax because it cannot be satisfied" |
| Regulation by F2,6BP | Fructose-6-phosphate → Phosphofructokinase 2 (active in fed state) → Fructose-2,6-bisphosphate → positive feedback → glycolysis Fructose-2,6-bisphosphate → Fructose bisphosphatase 2 (active in fasting state) → Fructose-6-phosphate → gluconeogenesis FBPase-2 and PFK-2 are part of the same complex but respond in opposite manner to phosphorylation by protein kinase A. Fasting state: ↑ glucagon → ↑ cAMP →↑ FBPase-2, ↓ PFK-2 Fed state: ↑ insulin →↓ cAMP →↓ protein kinase A →↓ FBPase-2, ↑ PFK-2 |
| Pyruvate dehydrogenase complex Reaction, 5 cofactors, activated by what, similar to what other complex | Reaction: pyruvate + NAD⁺ CoA → acetyl-CoA + CO₂ + NADH This complex contains 3 enzymes that require 5 cofactors: 1. Pyrophosphate (B₁, thiamine; TPP) 2. FAD (B₂, riboflavin) 3. NAD (B₃, niacin) 4. CoA (B₅, pantothenate) 5. Lipoic acid Activated by exercise: ↑ NAD⁺/NADH ratio ↑ ADP ↑ CA²⁺ This complex is similar to α-ketoglutarate dehydrogenase complex (same cofactors, similar substrate and action), which converts α-ketoglutarate → succinyl-CoA (TCA cycle). |
| ____ inhibits lipoic acid Findings (3) | Arsenic inhibits lipoic acid. Findings: vomiting, rice water stools, garlic breath |
| Pyruvate dehydrogenase deficiency Causes, findings, treatment | Causes backup of substrate (pyruvate and alanine), resulting in lactic acidosis. Can be congenital or acquired (as in alcoholics due to B₁ deficiency). Findings: neurologic defects Treatment: ↑ intake of ketogenic nutrients (e.g. high fat content or ↑ lysine and leucine) "Lysine and Leucine - the only purely ketogenic amino acids" |
| Pyruvate metabolism 4 different pathways | Pyruvate (from glucose) ↔ Alanine → Oxaloacetate → Acetyl-CoA ↔ Lactate Functions of different pyruvate metabolic pathways: 1. Alanine carries amino groups to the liver from muscle 2. Oxaloacetate can replenish TCA cycle or be used in gluconeogenesis 3. Transition from glycolysis to the TCA cycle 4. End of anaerobic glycolysis (major pathway in RBCs, leukocytes, kidney medulla, lens, testes, and cornea) |
| TCA cycle (Krebs cycle) Products, location, substrates | Pyruvate → acetyl-CoA produces 1 NADH, 1 CO₂ The TCA cycle produces: 3 NADH, 1 FADH₂, 2 CO₂, 1 GTP per acetyl-CoA = 12 ATP/acetyl-CoA (2x everything per glucose) TCA cycle reactions occur in the mitochondria. α-ketoglutarate dehydrogenase complex requires the same cofactors as the pyruvate dehydrogenase complex (B₁, B₂, B₃, B₅, lipoic acid). |
| TCA cycle components (8) | "Citrate Is Krebs' Starting Substrate For Making Oxaloacetate" Citrate Isocitrate α-Ketoglutarate Succinyl-CoA Succinate Fumarate Malate Oxaloacetate |
| Electron transport chain and oxidative phosphorylation | NADH electrons from glycolysis and the TCA cycle enter mitochondria via the malate-aspartate or glycerol-3-phosphate shuttle. FADH₂ electrons are transferred to complex II (at a lower energy level than NADH). The passage of electrons results in the formation of a proton gradient that, coupled to oxidative phosphorylation, drives the production of ATP. |
| ATP produced via ATP synthase: | 1 NADH → 3 ATP 1 FADH₂ → 2 ATP |
| Oxidative phosphorylation poisons Electron transport inhibitors Name 4, mechanism | Rotenone CN⁻ Antimycin A CO Directly inhibit electron transport, causing a ↓ proton gradient and block of ATP synthesis |
| Oxidative phosphorylation poisons ATPase inhibitors Name 1, mechanism | Oligomycin Directly inhibit mitochondrial ATPase, causing an ↑ proton gradient. No ATP is produced because electron transport stops |
| Oxidative phosphorylation poisons Uncoupling agents Name 3, mechanism | 2,4-DNP Aspirin (fevers often occur after aspirin overdose) Thermogenin in brown fat ↑ permeability of membrane, causing a ↓ proton gradient and ↑ O₂ consumption. ATP synthesis stops, but electron transport continues. Produces heat |
| Gluconeogensis, irreversible enzymes (4) | 1. Pyruvate carboxylase (mitochondria) 2. PEP carboxylase (cytosol) 3. Fructose-1,6-bisphosphatase (cytosol) 4. Glucose-6-phosphatase (ER) "Pathway Produces Fresh Glucose" |
| Gluconeogensis, irreversible enzymes Pyruvate carboxylase Location, reaction, requirements | Mitochondria [Pyruvate → oxaloacetate] Requires biotin, ATP. Activated by acetyl-CoA |
| Gluconeogensis, irreversible enzymes PEP carboxylase Location, reaction, requirements | Cytosol [Oxaloacetate → phosphoenolpyruvate] Requires GTP |
| Gluconeogensis, irreversible enzymes Fructose-1,6-bisphosphatase Location, reaction | Cytosol [Fructose-1,6-bisphosphate → fructose-6-P] |
| Gluconeogensis, irreversible enzymes Glucose-6-phosphatase Location, reaction | ER [Glucose-6-P → glucose] |
| Gluconeogensis, irreversible enzymes Which organ do these reactions occur? What happens if the enzymes are deficient? What are the contributions to gluconeogenesis by odd/even-chain fatty acids? | Occurs primarily in liver. Enzymes also found in kidney, intestinal epithelium. Deficiency of the key gluconeogenic enzymes causes hypoglycemia. (Muscle cannot participate in gluconeogenesis because it lacks glucose-6-phosphatase.) Odd-chain fatty acids yield 1 propionyl-CoA during metabolism, which can enter the TCA cycle (as succinyl-CoA), undergo gluconeogenesis, and serve as a glucose source. Even-chain fatty acids cannot produce new glucose, since they yield only acetyl-CoA equivalents |
| Hexose monophosphate (HMP) shunt (pentose phosphate pathway) Purpose, products, sites (4) | Purpose is to provide a source of NADPH from an abundantly available glucose-6-phosphate (NADPH is required for reductive reactions, e.g. glutathione reduction inside RBCs). Additionally, this pathway yields ribose for nucleotide synthesis and glycolytic intermediates. 2 distinct phases (oxidative and nonoxidative), both of which occur in the cytoplasm. No ATP is used or produced. Sites: 1. Lactating mammary glands 2. Liver 3. Adrenal cortex (sites of fatty acid or steroid synthesis) 4. RBCs |
| Hexose monophosphate (HMP) shunt (pentose phosphate pathway) Oxidative and Nonoxidative pathways | Oxidative (irreversible) Glucose-6-P → Glucose-6-P dehydrogenase (rate-limiting step) → → Products: Co₂, 2 NADPH, Ribulose-5-P Nonoxidative (reversible) Ribulose-5-P → Transketolases (requires B₁) → → Products: Ribose-5-P, G3P, F6P |
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