CHO Metabolism 2 PDF

Carbohydrates Metabolism 2  Oxidative decarboxylation of pyruvic acid: It occurs in the mitochondria. It is irreversible. It needs: 1) 3 enzymes (Pyruvate dehydrogenase complex). 2) 5 coenzymes (TPP, lipoic acid, COASH, FAD and NAD+). Krebs' cycle (citric acid cycle or tricarbo...

Carbohydrates Metabolism 2  Oxidative decarboxylation of pyruvic acid: It occurs in the mitochondria. It is irreversible. It needs: 1) 3 enzymes (Pyruvate dehydrogenase complex). 2) 5 coenzymes (TPP, lipoic acid, COASH, FAD and NAD+). Krebs' cycle (citric acid cycle or tricarboxylic acid cycle) Definition: It is the final common pathway for the complete oxidation of acetyl –CoA. Acetyl –CoA can result from the partial oxidation of CHO, lipid &protein. Site: Mitochondria of every cell. Summary of reactions: Regulation of Krebs’ cycle: The rate of Krebs’ cycle depends on the cell need for ATP.  ATP &  ADP, AMP & NAD in the cell → stimulation of Krebs’ cycle →  ATP production  ATP &  NADH in the cell → inhibition of Krebs’ cycle →  ATP production. Importance of Krebs’ cycle: 1- It is the major source of energy (oxidation of acetyl-COA (from CHO, lipid & protein)→ 12 ATPs). 2- Provides succinyl-COA (active succinate), which is important for: a. hemoglobin synthesis b. Ketolysis c. detoxification. 4- Supplies the body with substances which can give amino acids: a. Alanine from pyruvic acid. b. glutamic acid from --ketoglutaric acid c. aspartic acid from oxaloacetic acid  Energy from glucose oxidation 1) In absence of O2: only anaerobic (glycolysis) → 2 ATP. 2) In presence of O2: Glycolysis → 2 ATP + 2 NADH + 2 Pyruvate = 8 ATP 2 Pyruvate → 2 Acetyl-CoA + 2 NADH = 6 ATP 2 Acetyl-CoA = 6 NADH + 2 FADH + 2 ATP = 24 ATP So, the complete oxidation of 1 mol of Glucose → 38 ATP  Hexose monophosphate shunt (HMP- shunt) Definition: It is an alternative minor pathway for glucose oxidation involving the formation of pentoses as intermediates. Site: Cytosol of some cells (need NADPH): 1- Liver, adipose tissue & lactating mammary gland (F.A synthesis). 2- Adrenal cortex, gonads & placenta (steroid synthesis.( 3- RBCs a) keeps iron of hemoglobin in ferrous state. b) Keeps cell membrane resistant to hemolysis. 4- Retina, cornea, lens (reduction of retinal to retinol). Functions of HMP shunt: 1-production of NADPH+H+ (reduced coenzyme II) which is used in the: 1-synthesis of fatty acids. 2-synthesis of cholesterol. 3-synthesis of certain steroid hormones. 2-production of pentoses 5 -p (ribulose, xylulose &ribose 5-p) which is important in: 1-formation of nucleosides (base –pentose) 2-formation of nucleotides (base –pentose-p) 3-formation of nucleic acids and nucleo-protein.  Uronic Acid Pathway Site: Cytosol. Importance: This pathway supplies the body with glucuronic acid which is used in: Detoxication (bilirubin). Mucopolysaccharide formation. Thank You