Carbohydrate Metabolism (Lecture 3) PDF

DR. S. BRYAN GLYCOLYSIS Central metabolic pathway that is used by all cells for the oxidation of glucose to generate energy in the form of ATP (adenosine triphosphate) and intermediates for use in other metabolic pathways. This ten-step pathway occurs in the presence of specific enzymes in the liver...

DR. S. BRYAN GLYCOLYSIS Central metabolic pathway that is used by all cells for the oxidation of glucose to generate energy in the form of ATP (adenosine triphosphate) and intermediates for use in other metabolic pathways. This ten-step pathway occurs in the presence of specific enzymes in the liver (cell cytosol). Glycolysis occurs in the presence or absence of oxygen to enable aerobic and anaerobic cellular respiration. Products of glycolysis include pyruvate, NADH, and ATP which are vital for cell functions. GLYCOLYSIS PHASE 1: ENERGY INVESTMENT PHASE 2: ENERGY PAY-OFF ** **Committed step of Glycolysis** SUMMARY: Glycolysis Phase I (Energy utilization phase): Glucose (6-C) breaks down in 10 steps in glycolysis, to give 2 molecules of pyruvate (3-C). 2 ATP used up in steps 1 and 3 are replaced in step 7. Phase II (Energy recovery phase): The 2 molecules of glyceraldehyde-3-phosphate are converted to pyruvate under aerobic state with generation of 2 ATPs or lactate under anaerobic state. 2 ATP formed in step 10 and 2 NADH = the energy product of the glycolysis process. GLUCONEOGENESIS Metabolic pathway that results in the biosynthesis of glucose from certain non-carbohydrate carbon substrates. Gluconeogenesis supplies the needs for plasma glucose between meals. Gluconeogenesis occurs in the liver and kidneys. Non-carbohydrate precursors: lactate pyruvate glucogenic amino acids glycerol propionate Homolactic Fermentation Lactate formed from pyruvate via lactic acid fermentation. Utilized by muscles when the demand for ATP is high and oxygen availability is low. Gluconeogenesis from Lactate (Cori Cycle) A process by which glucose is converted to lactate in the muscle and in the liver. The lactate is then re-converted to glucose. In an actively contracting muscle, pyruvate is reduced to lactic acid which may tend to accumulate in the muscle. To prevent lactate accumulation because lactic acid is toxic, the body utilizes the Cori cycle. Lactate and the Cori Cycle REGULATION OF CARBOHYDRATE METABOLISM Glucose homeostasis is accomplished through two major hormones, glucagon and insulin. Glucagon is a hormone produced by the alpha cells of the pancreas. ØGlucagon: Inhibits glucose consuming pathways. to increase blood glucose levels Activates glycogen breakdown in liver. Stimulates gluconeogenesis and glycogenolysis REGULATION OF CARBOHYDRATE METABOLISM Insulin is a peptide hormone. Secreted by the beta cells of the pancreas. ØInsulin: stimulates glucose consuming processes. to decrease glucose levels increases absorption of glucose by cells increases the synthesis of glycogen stimulates glycolysis and glycogenesis DIABETES MELLITUS (DM) Diabetes mellitus is a chronic disorder characterized by derangements in carbohydrate, fat and protein metabolism. Elevated levels of glucose in blood (hyperglycaemia). 3 Main types of DM: Type 1 (5-10%)-unable to produce enough insulin Type 2 (90-95%)-insulin resistance (body does not respond well to insulin) Gestational – during pregnancy Other DM- Specific types of diabetes due to other causes DIABETES TESTING Oral glucose tolerance test (OGTT) A fasting blood sample and 2-hour postprandial sample (after a meal) are taken. Diagnosis of Diabetes mellitus: Fasting > 126 mg/dL and 2hr > 198 mg/dL The normal blood glucose value is: 65-100 mg/dL DIABETES TESTING -HbA1c Glycated or Glycosylated haemoglobin (HbA1C) test Glycated or Glycosylated Hb refers to the haemoglobin(Hb) which is bound to glucose. Test reflects average blood sugar level over 2-3 months. ≥ 6.5 % indicates diabetes mellitus New Technology: Continuous Glucose Monitoring (CGM) The CGM skin patch estimates glucose levels and wirelessly sends the information to a software program on a smartphone or insulin pump. The program calculates how much insulin your body needs, and the insulin pump delivers the insulin when glucose levels rise higher than your target range. (National Institute of Health, 2023) Synthesize glucose Use glucose for energy Study Check Identify each process: 1) glycolysis 3) glycogenolysis 2) glycogenesis 4) gluconeogenesis A. the synthesis of glucose from non-carbohydrates B. the breakdown of glycogen into glucose C. the oxidation of glucose to two pyruvate D. the synthesis of glycogen from glucose Solution Identify each process. 1) glycolysis 3) glycogenolysis 2) glycogenesis 4) gluconeogenesis A. the synthesis of glucose from noncarbohydrates B. the breakdown of glycogen into glucose C. the oxidation of glucose to two pyruvate D. the synthesis of glycogen from glucose 4) gluconeogenesis 3) glycogenolysis 1) glycolysis 2) glycogenesis