Carbohydrates Lecture 3 PDF

040817231 Introductory biochemistry Carbohydrates Nashwa W. yassa, PhD Polysaccharides Condensation products of more than ten monosaccharide units They are either linear α(1-4) linkage or branched α (1-6) linkage polymers. Examples starch, glycogen, cellulose, dextra...

040817231 Introductory biochemistry Carbohydrates Nashwa W. yassa, PhD Polysaccharides Condensation products of more than ten monosaccharide units They are either linear α(1-4) linkage or branched α (1-6) linkage polymers. Examples starch, glycogen, cellulose, dextran and inulin and chitin. Digestion of carbohydrates 2 types of enzymes are important for the digestion of carbohydrates Amylases Disaccharidases Convert polysacc. to disacc. Convert disacc. to monosacc. maltase Pancreatic Salivary amylase Sucrase amylase lactase Fates of the absorbed glucose The only sugar utilized by the body Absorbed through portal blood to the liver. The majority of it is taken by the liver to be stored as glycogen oxidized by glycolysis Glucose for acetyl CoA and lipid synthesis Minimal amount passes through systemic circulation to maintain BGL (the fasting BGL 70-110 mg/dl). Glucose is the preferred source of energy for most of the body tissues. Ex. Brain cells Carbohydrate Metabolism Carbohydrates catabolism includes Carbohydrates anabolism includes 1.Glycolysis 1.Gluconeogenesis 2.Krebs cycle 2.Glycogenesis 3.Pentose phosphate pathway 4.Glycogenolysis Carbohydrates Catabolism Glycolysis Is the breakdown of glucose in the cytoplasm of all body cells.  May be: a) Aerobic (in the presence of oxygen) Glucose 2 pyruvate + 8ATP b) Anaerobic (in the absence of oxygen) Glucose 2 Lactate+ 2ATP Krebs cycle  Also known as:  Citric acid cycle  Tricarboxylic acid cycle Occur in the mitochondria following aerobic glycolysis in which pyruvate Acetyl coA Enters Krebs cycle GLycolsis Conversion of pyruvate to acetyCoA (oxidative decarboxylation) Glycolysis summary Location :Cytosol Substrate :glucose C6H12O6 Product: 2 pyruvate ,2 ATP , 2NADH What happens to the 2 NADH produced during glycolysis? Sent to the ETC for further processing into lots of ATP by oxidative phosphorylation Pyruvate oxidation summary Location: ends up in mitochondrial matrix Substrate: 2 pyruvate Products: 2 acetyl coA, 2 NADH, 2 CO2  Location of pyruvate oxidation Moves the pathway into the mitochondrial matrix O2 needs of pyruvate oxidation? - does not consume O2 directly - BUT O2 is needed for the mitochondrion to be open for business What happens to the 2 acetyl coA made during pyruvate oxidation? 2 acetyl CoA enter the citric acid (Krebs) cycle What happens to the 2 NADH produced during pyruvate oxidation? Sent to the ETC for further processing into lots of ATP by oxidative phosphorylation Citric acid (Krebs) cycle summary Location: mitochondrial matrix O2 Needs: does not consume O2, but O2 is needed for mitochondrion to be open for business Substrate: 2 acetyl CoA Products: 2 ATP, 6 NADH, 2 FADH2, 4 CO2 Citric acid (Krebs) cycle summary Substrate(s) of Citric acid (Krebs) cycle? per starting glucose: 2 acetyl CoA (1 acetyl CoA per turn, so the cycle turns TWO times for every starting glucose) Product(s) of citric acid (Krebs) cycle? per starting glucose: - 2 ATP - 6 NADH - 2 FADH2 - 4 CO2 What makes the citric acid (Krebs) cycle a cycle? - Each of 2 acetyl CoA molecules combines with oxaloacetate (OAA) to form citrate - citrate is oxidized back to OAA in 7 more steps - OAA combines with the next acetyl CoA etc. Location of citric acid (Krebs) cycle? mitochondrial matrix  What happens to the 6 NADH and 2 FADH2 produced during the citric acid (Krebs) cycle? Sent to the ETC for further processing into lots of ATP by oxidative phosphorylation Function of NADH and FADH2 - carry high energy electrons harvested from food molecules - take them to the ETC for exergonic electron flow and ATP production by oxidative phosphorylation Gluconeogenesis  The synthesis of glucose from non- carbohydrate compounds is known as gluconeogenesis. The major substrates/precursors for gluconeogenesis: Lactate, pyruvate, glucogenic amino acids, Gluconeogenesis propianate and glycerol. Site: Gluconeogenesis occurs mainly in the liver, and to a lesser extent in the renal cortex. The pathway is partly mitochondrial & partly cytoplasmic. Importance of gluconeogenesis Brain & CNS, erythrocytes, testes & kidney medulla are dependent on glucose for continuous supply for energy. During starvation gluconeogenesis maintains the blood glucose level. The stored glycogen is depleted within the first 12-18 hours of fasting. On prolonged starvation, the gluconeogenesis is speeded up & protein catabolism provides the substrates, namely glucogenic amino acids. Human brain alone requires about 120 g of glucose per day, out of about 160 g needed by the entire body. Glucose is the only source that supplies to the skeletal muscle, anaerobic conditions. Reactions of gluconeogenesis Gluconeogenesis closely resembles the reversed pathway of glycolysis. The 3 irreversible steps of glycolysis are catalysed by the 3 enzymes. Hexokinase PFK Pyruvate kinase These three stages bypassed by alternate enzymes specific to gluconeogenesis. These are: Phosphoenol Fructose-1-6- Glucose-6- Pyruvate pyruvate bisphosphatase phosphatase carboxylase carboxy kinase Thanks