Biochemistry

• Glucose is the blood sugar, the focal point of carbohydrate metabolism, supplied to the body via circulatory system, can either be oxidized to yield energy or stored as glycogen for future use.
• Digestion is the breakdown of food molecules by hydrolysis into simpler chemical units that can be used by cells in their metabolic processes.
• In the mouth, salivary enzyme "Alpha-amylase" catalyzes the hydrolysis of alpha-glycosidic linkages of starch and glycogen to produce smaller polysaccharides and disaccharide - maltose.
• Only a small amount of carbohydrate digestion occurs in the mouth because food is swallowed so quickly into the stomach.
• In stomach, very little carbohydrate is digested due to lack of carbohydrate digestion enzymes and inactivation of salivary amylase by stomach acidity.
• The three types of enzymes are oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases.
• The primary site for the carbohydrate digestion is within the small intestine where pancreatic alpha-amylase breaks down polysaccharide chains into disaccharide - maltose.
• Oxidation-reduction reactions involve the transfer of electrons from one molecule to another.
• Transferase enzymes catalyze the transfer of functional groups between two substrates.
• The final step in carbohydrate digestion occurs on the outer membranes of intestinal mucosal cells where disaccharidase enzymes preset in the intestinal mucosa convert disaccharides (maltose, sucrose and lactose) to monosaccharides (glucose, fructose and galactose).
• Oxidoreductases catalyze reactions involving electron transfers between substrates.
• The principal function of glucagon is to increase blood glucose concentration by speeding up the conversion of glycogen to glucose (glycogenolysis) in the liver.
• Glucagon is a 29 amino acid peptide hormone produced in the pancreas by alpha cells and released when blood glucose levels are low.
• 6 B-Vitamins participate in various reactions of carbohydrate metabolism: Niacin, NAD+ and NADH, Riboflavin, as FAD, FADH2 and FMN, Thiamin, as TPP, Pantothenic acid, as CoA, Biotin, and Vitamin B6 in the form of PLP(pyridoxal 5-phosphate).
• The function of epinephrine is similar to glucagon, i.e., it stimulates glycogenolysis.
• The primary target of epinephrine is muscle cells, where it promotes energy generation for quick action.
• Epinephrine also functions in lipid metabolism.
• Structurally modified B-vitamins function as coenzymes in carbohydrate metabolism.
• Without these B-vitamins, the body would be unable to utilize carbohydrates as energy sources.
• Glucagon elicits the opposite effects of insulin.
• Epinephrine, also called adrenaline, is released by the adrenal glands in response to anger, fear, or excitement.
• Transferases catalyze group transfers from one compound to another.
• The carbohydrate digestion products (glucose, galactose, and fructose) are absorbed into the bloodstream through the intestinal wall.
• The intestinal villi are rich in blood capillaries into which the monosaccharides are actively transported.
• ATP hydrolysis and protein carriers mediate the passage of the monosaccharides through cell membranes.
• Galactose and Fructose are converted to products of glucose metabolism in the liver.
• Ethanol fermentation involves two reactions: Pyruvate decarboxylation by pyruvate decarboxylase and Acetaldehyde reduction to ethanol by alcohol dehydrogenase.
• The purpose of lactate fermentation is the conversion of NADH to NAD + for increased rate of glycolysis.
• Both pyruvate kinase (Step 10) and phosphofructokinase (Step 3) are allosteric enzymes.
• Enzymatic anaerobic conversion of pyruvate to ethanol and carbon dioxide occurs in simple organisms, e.g., yeast and bacteria, to regenerate NAD +.
• Ethanol fermentation involving yeast causes bread and related products to rise as a result of CO2 bubbles being released during baking.
• Three reactions exhibit particularly large decreases in free energy; the enzymes that catalyze these reactions are sites of allosteric control: Hexokinase, Phosphofructokinase, Pyruvate kinase.
• Under aerobic (oxygen-rich) conditions, pyruvate is oxidized to acetyl CoA by pyruvate dehydrogenase complex.
• An enzymatic anaerobic reduction of pyruvate to lactate occurs mainly in muscles.
• Acetyl CoA thus formed enters the mitochondrial matrix for further processing through the citric acid cycle.
• The overall ethanol fermentation reaction is: Glucose + 2 ADP + 2 Pi → 2Ethanol + 2 CO2 + 2 ATP + 2H2O.
• Most pyruvate formed during glycolysis is converted to Acetyl CoA.
• Lactate is converted back to pyruvate when aerobic conditions are reestablished in the cell.
• NAD + needs to be recycled to prevent decrease in oxidation reactions.
• Beer, wine, and other alcoholic drinks are produced by ethanol fermentation of the sugars in grain and fruit products.