BIOCHEM - CARBOHYDRATE METABOLISM

• Carbohydrates are a major source of energy for human beings.
• Physiologically, glucagon signifies the starved state.
• The molecule glucose, commonly known as blood sugar, is the focal point of carbohydrate metabolism.
• Glucose is supplied to the body via the circulatory system and, after being absorbed by a cell, can be either oxidized to yield energy or stored as glycogen for future use.
• When sufficient oxygen is present, glucose is totally oxidized to CO2 and H2O.
• In the absence of oxygen, glucose is only partially oxidized to lactic acid.
• Glucose and other six-carbon sugars can be converted into a variety of different sugars (C3, C4, C5, and C7) needed for biosynthesis.
• Some of the oxidative steps in carbohydrate metabolism also produce NADH and NADPH, sources of reductive power in cells.
• The different clinical metabolic concerns on carbohydrate metabolism, such as with regards to diabetes mellitus and many other related disorders, will also be correlated in this module.
• In this module, the relationship between carbohydrate metabolism and energy production in cells will be explored.
• The molecule glucose is the focal point of carbohydrate metabolism.
• Hormonal control is a second major method for regulating carbohydrate metabolism, besides enzyme inhibition by metabolites.
• Epinephrine, also called adrenaline, is released by the adrenal glands in response to anger, fear, or excitement and functions similarly to glucagon, stimulating glycogenolysis, the release of glucose from glycogen.
• Epinephrine acts by binding to a receptor site on the outside of the cell membrane, stimulating the enzyme adenyl cyclase to begin production of a second messenger, cyclic AMP (cAMP) from ATP.
• Glucagon, a polypeptide hormone (29 amino acids) produced in the pancreas by alpha cells, is released when blood-glucose levels are low and increases blood-glucose concentrations by speeding up the conversion of glycogen to glucose (glycogenolysis) and gluconeogenesis in the liver.
• Insulin, a 51-amino-acid protein hormone, is produced by the beta cells of the pancreas and promotes the uptake and utilization of glucose by cells, lowering blood-glucose levels.
• The cAMP is released in the cell interior, where, in a series of reactions, it activates glycogen phosphorylase, the enzyme.
• Glucose, commonly known as blood sugar, is supplied to the body via the circulatory system and, after being absorbed by a cell, can be either oxidized to yield energy or stored as glycogen for future use.
• Glycolysis is a linear pathway that takes place in the cytosol of a cell.
• The glycolytic pathway is an isomerization type of reaction.
• In the process of glycolysis, glucose gets a phosphate from ATP to make glucose - 6 - phosphate (G6P) and later fructose - 6 - phosphate (F6P) gets another phosphate from ATP to make fructose - 1,6 - bisphosphate (F1,6BP).
• Each pyruvate molecule loses a carboxylic group in the form of carbon dioxide.
• The fate of the pyruvate molecules depends on whether oxygen is present.
• The remaining two carbons are then transferred to the enzyme CoA to produce Acetyl CoA.
• Glycolysis produces 2 ATP, 2 NADH, and 2 pyruvate molecules.
• The conversion of pyruvate to acetyl CoA is a three - step process.
• If oxygen is present, the pyruvates are transported into the mitochondrial matrix.
• In cells with mitochondria and oxidative metabolism, pyruvate is converted into ACETYL COA (precursor to kreb cycle) and completely into CO2 and H2O (in kreb cycle) – glycolysis in this setting is termed aerobic glycolysis.
• Molecular oxygen is not needed in glycolysis.
• If oxygen isn't available, the pyruvate is converted to lactate, and no additional ATP is produced from this conversion.
• In RBCs, which lack mitochondria and oxidative metabolism, pyruvate is reduced to lactic acid, a three - carbon hydroxyacid, the product of anaerobic glycolysis.
• Glucagon and epinephrine increase blood-glucose levels.
• Oxidation is a reaction in the glycolytic pathway.
• Phosphorylation of ADP is not a reaction in the glycolytic pathway.
• In the human body, under oxygen rich and oxygen poor conditions, respectively, pyruvate is converted to lactate and acetyl CoA.
• CO 2 is not produced in the conversion of pyruvate to lactate.
• Cleavage Dehydration is not a reaction in the glycolytic pathway.
• Insulin promotes the uptake and use of glucose by cells.
• Dihydroxyacetone phosphate is converted to 2 glyceraldehyde 3 - phosphate, marking the beginning of the glycolytic pathway.
• Isomerization is not a reaction in the glycolytic pathway.