BBMB 405 1st Edition Lecture 5Outline of Last Lecture VII. Chapter 20: The Calvin Cycle and the Pentose Phosphate PathwayC. The pentose phosphate Pathway Generates NADPH and Synthesizes Five-Carbon Sugars (1/21)VIII. Summary of Calvin CycleIX. Handout: Physiological significance of hexose monophosphate pathway (pentose phosphate pathway)Outline of Current Lecture VII. Chapter 20: The Calvin Cycle and the Pentose Phosphate PathwayC. The pentose phosphate Pathway Generates NADPH and Synthesizes Five-Carbon SugarsD. The metabolism of Glucose 6-phosphate by pentose Phosphate pathway Is coordinated with glycolysisX. Handout: (1/23)Current LectureVII. Chapter 20: The Calvin Cycle and the Pentose Phosphate PathwayC. The pentose phosphate Pathway Generates NADPH and Synthesizes Five-Carbon Sugars1. Mechanism: transketolase and transaldolase stabilize carbanionic intermediates by different mechanismsa. Transketolase mechanismThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. Transaldolase reactionD. The metabolism of Glucose 6-phosphate by pentose Phosphate pathway Is coordinated with glycolysis1. Metabolic control of pentose phosphate pathway (either glycolysis or pentose)a. Cytoplasmic concentration of NADP+ plays role in determining fate of glucose 6-phosphate: G-6-P is converted to 6-PG via NADPH, rate limiting stepb. Non oxidative reaction controlled by [substrate] and [product] of each reaction2. The rate of pentose phosphate pathway is controlled by level of NADP2a. First step in oxidative branch of PPP (pentose phosphate pathway) is the dehydrogenation of G 6-P and is irreversible, that is why NADPH is limitingcofactorb. Effect or importance of NADPH/NADP+: Ratio of NADP+ and NADPH in liver cell of rat is 0.014, which is several orders of magnitude lower than ration of NAD1 to NADH (which is 700), effect on rate of oxidative phase ensures that NADPH is not made unless needed supply is low3. The flow of glucose 6-phosphate depends on the need for NADPH, ribose 5-phosphate, and ATPa.b. Mode 1: R-5-P need > NADPH need, generates intermediates, used in rapidly dividing cells (cancer cells) need to replicate DNA quickly, 5 Glucose 6-phosphate + ATP → 6 ribose 5-phosphate + ADP + 2 H+c. Mode 2: NADPH need = R-5-P need, used in liver for synthesis such as cholesterold. Mode 3: NADPH need >> R-5-P need, functions as a cycle, used in red blood cells (need lots of NADPH and has no DNA/RNA) and adipose tissuefor synthesis of fatty acids, the glucose 6-phosphate can be completely oxidized to carbon dioxide with generation of NADPH,e. Mode 4: Both NADPH and ATP needed, intermediates converted to pyruvate and burned, used in developing brain (still going through cell division) or major cell division (red blood cells, epithelial cells, bone marrow),4. Through the looking-glass: the Calvin cycle and the pentose phosphate pathway are mirror images, look at them as similar and use that to help you study them, many enzymes are common to both cyclesX. Handout: (1/23)A. Reduction of O21. Complete Reduction: O2 + 4H+ + 4e- --ETS 2H2O2. Incomplete reduction (oxidative stress causes problems in the body): O2 + e- Superoxide ion (very reactive) O2- + e- Peroxide ion O22- + 2H+ Hydrogen peroxide H2O23. Protection against reactive oxygen species (ROS)a. 2O2- + 2H+ --superoxide dismutase (SOD) O2 + H2O2b. SOD is deficient in ALS patientsc. 2H2O2 –catalase O2 + 2H2Od. H2O2 + AH2 –peroxidase 2H2O + Ae. AH2 = glutathione, vitamin C, cytochrome C, quinonesf. Two reactions of catalase (see handout)4. Protection with vitamin E and C (react with O22-)B. Peroxidase/catalase as protectant in bombardier beetlea. 25% H2O2 Hydroquinone + Peroxidase Catalase Hot boiling H2Ob. 3H2O2 + hydroquinone Quinone + 4H2O + O2 + heatC. Electron Transport System and free radicalsa. See handout for radical reactionb. Vitamin E protects against radicals, neutralizes themc. Rancidityd. Lipid peroxidation in tissues, free radicals steal electrons from lipids in cell membrane and cause cell damagee. Malondialdehyde is used to measure peroxidation in tissuesD. G-6-P dehydrogenase deficiencya. Inherited x-linked recessive disorderb. Cause: G-6-P dehydrogenase deficiency causes low [NADPH], leading to cells being very sensitive to oxidative stress. Low [NADPH] means low [GSH}, which is needed for reducing H2O2 via GSH peroxidasec. Symptom: oxidative stress in RBC Hemolytic anemia (too many cells break to fast) recover: new RBCd. Stress increases (via drugs or infection) need of NADPH so increase productione. Diagnosis: assay of G-6-P dehydrogenase activity in RBCf. Resistance to malaria: lower infection in people with deficiency (sickle cell anemia)E. Glycogen Metabolisma. 10% of glycogen metabolism takes place in the liverb. Major enzymes of glycogen metabolism:i. Synthesis: glycogen synthase, branching enzymeii. Degradation: phosphorylase, debranching enzyme (alpha-1,6 glucosidase and transferase)c. See handoutF. Carl and Gerty Cori
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