Carbohydrate Metabolism Lecture Notes PDF

Almaaqal University Carbohydrate Metabolism Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-8  Carbohydrate metabolism Metabolis m is the total amount of the biochemical r...

Almaaqal University Carbohydrate Metabolism Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-8  Carbohydrate metabolism Metabolis m is the total amount of the biochemical reactions that take place within each cell of living Metabolism organisms and provide energy for vital processes and for synthesizing new organic material. There are two type of metabolic process (anabolism and catabolism). Anabolism Anabolism is a biochemical process which includes building up large complex molecules from simple molecules. The anabolic state represents the growth of muscles, bones, and other body structures. It consumes energy through ATP hydrolysis. Catabolism Catabolism It is a process where large complex molecules are broken down into smaller ones releasing energy. For example, glycolysis involves producing energy from glucose derived from complex carbohydrate biomolecules.  Fate of glucose after absorption In the liver, glucose undergoes variety of chemical changes depending upon the physiological need of the body. 1. Body need for energy: glucose oxidized completely to CO2, H2O and energy by (glycolysis and citric acid cycle). 2. Excess glucose may be converted to glycogen, deposit in liver, muscle tissues By ( glycogenesis). 3. To maintain glucose blood level, liver glycogen reconverted to glucose enters blood By (glycogenolysis).  4. Excess glucose after conversion to glycogen , convert to fatty acids stored in adipose tissue as triglycerides (lipogenesis). 5. Small amounts of glucose may be utilized for the synthesis of ribose and deoxyribosee for synthesis of nucleic acids. 6. In muscle contraction, only partial degradation of glucose may take place, resulting in formation of lactic acid disposed off by the liver. The metabolism of CHO may be subdivided in the following categories. Glycolysis 1. It is the metabolic pathway that converts glucose into pyruvate. 2. It produces two molecules of pyruvate, ATP, NADH and water. 3. The process takes place in the cytosol (cytoplasm) of a cell and does not require oxygen. 4. The glucose in the blood circulation, when enter the cell become phosphorylated given by ATP. This phosphorylation occurs on the cell membrane by the action of two enzymes. 1. Specific enzyme (glucokinase) in the liver. 2. Nonspecific enzyme ( hexokinase ), Present in liver and other extra hepatic cell The reaction is irreversible.  Glycogenesis (glycogen synthesis): Glycogenesis: formation of glycogen from glucose. 1. Glycogen is serves as an energy store primarily in muscle and liver, when glucose and ATP are present in relatively high amounts. 2. The excess of insulin promotes the glucose conversion into glycogen for storage in liver and muscle cells. 3. It is stored in the form of granules in the cytoplasm of the cell. 4. Glycogen is an energy reserve that can be quickly mobilized to meet a sudden need for glucose  Glycogenolysis Glycogenolysis: biochemical breakdown of glycogen to glucose. 1. take place in the cells of muscle and liver tissues in response to hormonal and neural signals. 2. Glycogenolysis occurs in the cytoplasm and is stimulated by glucagon and adrenaline hormones. 3. Glycogenolysis plays an important role in the regulation of glucose levels in the blood.  Gluconeogenesis Gluconeogenesis: is the process of producing glucose from non-carbohydrate sources. 6 ATP molecules are consumed per molecule of glucose produced. Most reactions of the gluconeogenesis take place in the cytoplasm while two reactions occur in the mitochondria It mainly occurs in hepatocytes in liver. The molecules that provide substrates for gluconeogenesis include proteins, lipids and pyruvate.  Glycolysis and the control of hepatic glucose production (A) During fasting, rates of glycolysis in the liver are decreased, which are accompanied by a decrease in rates of glycogenesis and increases in rates of gluconeogenesis and glycogenolysis. These pathways leads to an increase in hepatic glucose production (HGP). (B) In response to feeding, rates of glycolysis are increased, which are accompanied by an increase in rates of glycogenesis and decreases in rates of gluconeogenesis and glycogenolysis. These pathways leads to suppression of HGP. Maltase Sucrase Lactase  Insulin Insulin is the principle hormone affecting blood glucose levels.  It facilitates glucose entry into the cells.  Insulin causes cells in the liver, skeletal muscles, and fat tissue to take up glucose from the blood.  In the liver and skeletal muscles, glucose is stored as glycogen, and in fat cells (adipocytes) it is stored as triglycerides. Diabetes (hyperglycemia) results from an inability of insulin to be produced or secreted. Glucagon: Glucagon is a hormone that is produced by the pancreas. Glucagon is released in response to low blood glucose levels. It stimulates the liver to break down glycogen to be released into the blood as glucose. Glucagon activating gluconeogenesis, the conversion of amino acids into glucose. Breaking down stored fat (triglycerides) into fatty acids for use as fuel by cells Human disease of carbohydrate metabolism are: 1. Diabetes mellitus 2. Lactose intolerance 3. Fructose intolerance 4. Galactosemia 5. Glycogen storage disease