Carbohydrates Metabolism PDF

CARBOHYDRATES PART 2: METABOLISMS Metabolism  Sum of all enzymatic reactions occurring in biological systems.  Involves energy transformation; it tells how energy is acquired, transformed, used and stored in a cell. Phases of Metabolism 1. Catabolism - degradative phase or breaking dow...

CARBOHYDRATES PART 2: METABOLISMS Metabolism  Sum of all enzymatic reactions occurring in biological systems.  Involves energy transformation; it tells how energy is acquired, transformed, used and stored in a cell. Phases of Metabolism 1. Catabolism - degradative phase or breaking down process. - metabolic pathway that leads to the decomposition of large complex molecules into small molecules. - often accompanied by release of energy; energy producing process. Ex. (CH2O)n, proteins, fats CO2, H2O, NH3, Urea. Phases of Metabolism 2. Anabolism - biosynthetic phase or building process. - metabolic pathway where in large complex organic molecules are constructed from small molecules. - often requires the input of energy; energy consuming process. Ex. Pyruvate, glucose, CO2 (CH2O)n, proteins, fats Sources of Caloric Energy 1. Carbohydrates 1 g = 4 kcal 2. Fats 1g = 9 kcal 3. Protein 1g = 4 kcal Average Filipino Diet 55 – 65% Carbohydrates 15 – 20% Fats 5 – 15% Protein  Digestion of carbohydrates – Top – Early digestion depicting the intake of dietary carbohydrates and the role of salivary amylase  Digestion of carbohydrates Middle – Luminal digestion showing the combined roles of the stomach, pancreas and intestine.  -amylase -amylase etc. 1→6 etc. 1→4 Maltotriose -Amylase, of salivary or pancreatic origin, cleaves amylopectin to produce all of the products shown  -amylase -amylase etc. 1→6 1→4 -limit dextrin (branched oligosaccharide; unbranched also produced) -Amylase, of salivary or pancreatic origin, cleaves amylopectin to produce all of the products shown  etc. -amylase -amylase 1→6 1→4 Maltose Glucose -Amylase, of salivary or pancreatic origin, cleaves amylopectin to produce all of the products shown  Digestion of carbohydrates Bottom – Summary of the brush border glycoprotein complexes containing disaccharidases and oligosachharidases. Carbohydrates Metabolism  Is centered on the provision and fate of glucose  Glucose is known as blood sugar; dextrose.  One major pathway for the utilization of glucose is GLYCOLYSIS. GLYCOLYSIS  Is localized in the cytosol (soluble portion of the cytoplasm) of all cells.  It is a unique pathway, since it can utilize O2 if available (Aerobic) or it can function in the total absence of O2 (Anaerobic).  In aerobic condition the end product is Pyruvate.  In anaerobic condition, the end product is Lactate. ARSENATE/Pi=1-ARSENO- 3-PHOSPHOGLYCERATE Mn2+ ATP  Stands for Adenosine Triphosphate  It is composed of Adenine (Nitrogenous base), Ribose (5 C sugar) and Phosphate group. Role of ATP  Food and oxygen react chemically to produce energy. (food is oxidized to release energy)  Oxidation of food in the cells is also known as CELLULAR RESPIRATION.  The energy produced during Cellular Respiration is trapped in molecules of ATP.  ATP supplies the energy needed for all activities of the cells. How is ATP produced in biological system? Two types of ATP Production 1. Oxidative Phosphorylation - production of ATP through redox reactions in the mitochodria by the way of Electron Transport Chain (E.T.C) 1 mol NADH → E.T.C.→ 3 ATPs 1 mol FADH2→E.T.C.→ 2ATPs How is ATP produced in biological system? 2. Substrate Level Phosphorylation - production of ATP at the substrate level. Kreb’s Cycle sequence of reactions in mitochondria oxidizes the acetyl moiety of acetyl-CoA reduces coenzymes that are reoxidized through the electron transport chain final common pathway for the oxidation of carbohydrate, lipid, and protein Kreb’s Cycle  Acetyl CoA comes from pyruvate produce in aerobic glycolysis.  Rxn for pyruvate conversion to Acetyl CoA: CH3COCOO + NAD+ + CoASH (Pyruvate) (CoenzymeA) CH3COSCoA + CO2 + NADH (Acetyl CoA)  REGULATORY STEP -NADH,SUCCINYL COA REGULATORY STEP: +ADP,Ca REGULATORY STEP: -NADH,ATP -NADH,SUCCINYL COA Gluconeogenesis  Synthesis of glucose from non carbohydrate sources.  Major substrates are: 1. Glucogenic amino acids 2. Lactate 3. Glycerol 4. Propionate Major tissues involved: liver and kidney. Biomedical Importance of Gluconeogenesis Response the needs of the body for glucose when carbohydrate is not available in sufficient amounts from the diet. A continual supply of glucose is necessary as a source of energy, especially for the nervous system and the erythrocytes (red blood cells). Biomedical Importance of Gluconeogenesis  Brain is highly dependent on glucose as the primary fuel. Below a critical blood glucose concentration, brain will malfunctioned, which can lead to coma and death. Biomedical Importance of Gluconeogenesis  Glucose is also required in adipose tissue (fat tissue) as a source of glyceride, and plays a role in maintaining the level intermediates of the Kreb’s cycle in many tissue. Biomedical Importance of Gluconeogenesis  Glucose is the only fuel that will supply energy to skeletal muscles under anaerobic conditions.  Glucose is the precursor of milk sugar (lactose) in the mammary gland, and is taken up actively by the fetus. Gluconeogenesis  Gluconeogenesis involves glycolysis, citric acid cycle plus some special reactions.  Carbon atoms for gluconeogenesis from lactate, some amino acids, and glycerol are converted to pyruvate or other intermediates.  Seven reactions are the reverse of glycolysis and use the same enzymes. Gluconeogenesis  Special reactions: 1. Pyruvate to Oxaloacetate 2. Oxaloacetate to Phosphoenolpyruvate 3. Fructose 1,6 – bisphosphate to Fructose 6- phosphate 4. Glucose 6 - phosphate to Glucose Gluconeogenesis: Glucose Synthesis  Cori Cycle  When anaerobic conditions occur in active muscle, glycolysis produces lactate.  The lactate moves through the blood stream to the liver, where it is oxidized back to pyruvate.  Gluconeogenesis converts pyruvate to glucose, which is carried back to the muscles.  The Cori cycle is the flow of lactate and glucose between the muscles and the liver. Cori Cycle Glycogen Metabolism Glycogen is the human storage glucan polysaccharide.  In a 70kg adult: 80g in liver 260g in skeletal muscles. Glycogen Metabolism  Hepatic glycogen serves to maintain the blood glucose concentration particularly between meals.  Muscle glycogen serves only as an energy reserve for muscle activity. Glycogen molecules are branched chains of α14-linked glucose residues held together via α16 linkages. α14 linkages α16 linkage (branch point) α14 linkages Glycogen Metabolism 1. Glycogenesis 2. Glycogenolysis Glycogenesis  Synthesis of glycogen from glucose  It is carried out by the enzyme glycogen synthase  Occurs when there is excess of glucose in the body thus helps in the control of glucose in the blood  Is stored in the liver  Occurs in all the tissues of the body but the major sites are liver and muscles Glycogenesis Glycogenesis  Glycogen Metabolism Glycogenolysis is the break down of glycogen to glucose. Gycogenolysis Glycogenolysis Regulation of Glycogen Metabolism  Glucagon and insulin are major regulators of glycogen metabolism.  Adrenaline also has an important role in regulating breakdown of glycogen.  Hormonal regulation of carbohydrate metabolism proceeds via complex intracellular signalling cascades involving phosphorylation and dephosphorylation of proteins. Regulation of Glycogen Metabolism  Glucagon stimulates breakdown of glycogen resulting in release of glucose into the blood.  Glucagon has a short half-life in the blood (c. 5min). This enables rapid changes in glycogen metabolism to suit to the body’s needs. Regulation of Glycogen Metabolism  Glucagon causes: inhibition of glycogen synthesis stimulation of glycogen breakdown  These processes result in release glucose from the liver. Regulation of Glycogen Metabolism  INSULIN REVERSES THE EFFECTS OF GLUCAGON ON GLYCOGEN METABOLISM  Insulin receptors are present on liver, muscle and fat cells (adipocytes). stimulates glycogen synthesis stimulates glycolysis inhibits gluconeogenesis. Regulation of Glycogen Metabolism  ADRENALINE (EPINEPHRINE) STIMULATES BREAKDOWN OF GLYCOGEN TO GLUCOSE IN THE LIVER AND MUSCLES  Adrenaline stimulates glycogen breakdown via protein phosphorylation  Adrenaline-mediated protein phosphorylation results in glycogen breakdown to glucose and release of glucose from the liver into the bloodstream. D:\carbohydrate\carbohydrate\53.jpg Flight or Fight Response  This is the body's response to perceived threat or danger. During this reaction, certain hormones like adrenalin and cortisol are released, speeding the heart rate, slowing digestion, shunting blood flow to major muscle groups, and changing various other autonomic nervous functions, giving the body a burst of energy and strength. Pathways for Glucose “The End”