Matriz de Contenido del Curso y Ciclo de Ácidos

Biochemistry 1 for Technologists - Metabolism

• This course covers the digestion and absorption of carbohydrates, lipids, and proteins, and metabolic pathways.
• It explains how the body controls these pathways and discusses the importance of carbohydrates and lipids as energy sources.
• It details lipid transport, causes of hypercholesterolemia, fatty liver, and the biochemical causes of hyperammonemia and abnormal blood urea.

Carbohydrate Metabolism

• Carbohydrates provide 50% of daily calories, and complete oxidation of 1 gram of carbohydrates gives 4 kcal.

• Sources include starch, sucrose, lactose, fructose, and glucose from various food sources.

• Digestion involves enzymes like salivary amylase, pancreatic amylase, and intestinal disaccharidases to convert polysaccharides and disaccharides into monosaccharides (glucose, fructose, galactose).

• Lactose intolerance is caused by a deficiency of the lactase enzyme, leading to lactose accumulation in the intestines, causing symptoms like abdominal discomfort, cramps, and diarrhea.

• Metabolic pathways of carbohydrates include glycolysis, oxidative decarboxylation, Krebs cycle (citric acid cycle), hexose monophosphate shunt (HMP shunt), and the uronic acid pathway.

• Key regulatory enzymes of glycolysis: hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase.

• Glycolysis occurs in the cytoplasm of all cells and has importance in tissues lacking mitochondria or with reduced oxygen availability.

• Glycolysis involves 2 stages with energy-requiring and energy-producing steps.

• It produces 2 ATP in anaerobic conditions and 6-8 ATP in aerobic conditions

• Glucose uptake in RBCs does not depend on insulin.

• BPG (2,3-biphosphoglycerate) production also takes place in RBCs.

• The uronic acid pathway involves converting glucose into glucuronic acid. This is used in glycosaminoglycans synthesis, Vitamin C synthesis (in animals not humans), and detoxification reactions.

• Glycogen metabolism encompasses glycogenolysis and glycogenesis:

• Glycogenolysis breaks down glycogen into glucose-1-phosphate for energy release.

• Glycogenesis synthesizes glycogen from glucose.

• Regulation of glycogenesis and glycogenolysis is regulated during fasting (epinephrine) and meals (insulin).

• The metabolism of other hexoses, including fructose and galactose, are also important components of carbohydrate metabolism.

Lipid Metabolism

• Important aspects of lipid metabolism include digestion and absorption, fatty acid synthesis and oxidation, ketone body metabolism, and cholesterol and bile acid metabolism.
• Digestion of fats and lipids involves enzymes like lingual lipase (in the mouth), gastric lipase (in the stomach) and pancreatic lipase (in the intestines); converting triacylglycerol (TAGs) into free fatty acids & 2-monoacylglycerol
• Cholesterol esters are broken down by cholesterol esterase into cholesterol and fatty acids.
• Phospholipids are hydrolyzed by phospholipases into their component parts.
• Lipid absorption includes hydrolysis and absorption of lipids directly into the bloodstream for short/medium chain fatty acids, while hydrophobic lipids, including long-chain fatty acids, form micelles aiding in the absorption.
• The liver synthesizes and secretes lipoproteins into the bloodstream.
• These lipoproteins include chylomicrons, VLDL, IDL, LDL, and HDL.
• Key lipoproteins transport lipids like triglycerides.
• Cholesterol enters cells and is converted into cholesterol esters, then used in plasma membrane synthesis and steroid hormone production,
• Fatty acid synthesis (lipogenesis) occurs in the cytoplasm
• FA synthesis includes acetyl CoA carboxylase, forming malonyl CoA, and fatty acid synthase.
• Regulation of FA synthesis is dependent on nutritional state, allosteric regulation (citrate activating and long-chain acyl CoA inhibiting), and hormonal regulation (glucagon inhibiting and insulin stimulating).
• Microsomal pathways for FA synthesis are also discussed.

Protein Metabolism

• Protein digestion in the stomach begins with HCL and pepsin, which breaks down proteins.
• In the intestines, pancreatic enzymes like trypsin, chymotrypsin, and elastase break down polypeptides.
• Aminopeptidases and dipeptidases in the intestines further break down the resulting peptides into amino acids.
• Amino acids are absorbed through active transport or passive diffusion.
• Protein metabolism involves protein turnover, which is the continuous degradation and synthesis of proteins, and catabolism of amino acid nitrogen, including transamination and deamination.
• Transamination: transfer of amino groups from amino acid to a-ketoglutarate to obtain glutamate, which loses ammonia through deamination
• Deamination: removal of amino groups forming ammonia
• The urea cycle is the major pathway for ammonia removal, processing it into urea for excretion.
• The Urea cycle occurs in the liver and involves five amino acids (ornithine, citrulline, aspartate, arginine, and argininosuccinate), producing urea as the primary nitrogenous waste product.
• The chapter covers the metabolism of various individual amino acids, including glycine, phenylalanine, tyrosine, tryptophan, histidine, arginine, ornithine, lysine, hydroxylysine, serine and threonine, including their sources and pathways.
• Specific aspects of amino acid metabolism (e.g., synthesis and catabolism) and their roles in various biological processes are also included.