– Metabolism is a term that describes all the chemical reactions that occur in the cells of living organisms to maintain their life functions.
– Metabolism can be divided into two main types: catabolism and anabolism.
🔅 Catabolism
– This is the process of breaking down complex molecules into simpler ones, releasing energy in the process.
🔅 Anabolism
– This is the process of building up complex molecules from simpler ones, using energy in the process.
– Both types of metabolism are essential for growth, development, repair, and survival of living organisms.
Metabolism involves many different pathways and enzymes that regulate the rate and direction of chemical reactions.
– Metabolic pathways are sequences of chemical reactions that convert one substance into another, usually involving intermediate products called metabolites.
– Enzymes are proteins that catalyze or speed up the chemical reactions by lowering the activation energy required. Enzymes are often regulated by feedback mechanisms that control the amount and activity of the enzymes according to the needs of the cell.
– Metabolism can be influenced by various factors, such as genetics, hormones, diet, exercise, temperature, and drugs. Some of these factors can affect the expression and function of enzymes and metabolic pathways, altering the speed and efficiency of metabolism. For example:
🔅 Genetics can determine the variations in enzyme structure and activity among individuals, affecting their metabolic rate and susceptibility to certain diseases.
🔅 Hormones can regulate metabolism by stimulating or inhibiting certain enzymes and pathways, such as thyroid hormone, insulin, glucagon, and adrenaline.
🔅 Diet can affect metabolism by providing or limiting the availability of substrates and cofactors for metabolic reactions, such as carbohydrates, fats, proteins, vitamins, and minerals.
🔅 Exercise can increase metabolism by increasing the demand for energy and oxygen in the muscles and other tissues, stimulating the breakdown of glycogen and fat stores.
🔅 Temperature can affect metabolism by changing the kinetic energy and stability of molecules and enzymes, affecting their reaction rates.
🔅 Drugs can affect metabolism by interfering with or enhancing the action of enzymes and pathways, altering the production or elimination of metabolites.
– Metabolism is a complex and dynamic process that involves many different substances and reactions in living organisms.
– Some of the major substances that are metabolized in humans are:
Glucose
– Glucose is a simple sugar that is the main source of energy for most cells in the body. Glucose is obtained from the digestion of carbohydrates in food or from the breakdown of glycogen (a storage form of glucose) in the liver and muscles.
– Glucose is transported by the blood to various tissues where it is metabolized by glycolysis (a pathway that converts glucose into pyruvate), producing ATP (adenosine triphosphate), NADH (nicotinamide adenine dinucleotide), and H+ (hydrogen ions). Pyruvate can then enter different pathways depending on the availability of oxygen and the needs of the cell.
– In aerobic conditions (presence of oxygen), pyruvate enters the mitochondria (the organelles that produce most of the energy in cells) where it is converted into acetyl-CoA (acetyl coenzyme A) by pyruvate dehydrogenase complex (PDC), producing NADH and CO2 (carbon dioxide). Acetyl-CoA then enters the citric acid cycle (also known as Krebs cycle or tricarboxylic acid cycle), a pathway that produces more ATP, NADH, FADH2 (flavin adenine dinucleotide), CO2, and H2O (water). The NADH and FADH2 then enter the electron transport chain (ETC), a series of complexes that transfer electrons from NADH and FADH2 to O2, producing more ATP and H2O.
– In anaerobic conditions (without/ absence of oxygen), pyruvate is converted into lactate by lactate dehydrogenase (LDH), producing NAD+. Lactate is then transported to the liver where it is converted back to glucose by gluconeogenesis (a pathway that produces glucose from non-carbohydrate sources), completing the Cori cycle.
Fatty acids
– Fatty acids are long chains of carbon atoms with a carboxyl group (-COOH) at one end.
– Fatty acids are obtained from the digestion of fats in food or from the breakdown of triglycerides (a storage form of fat) in adipose tissue (fat cells). Fatty acids are transported by albumin (a protein) in the blood to various tissues where they are metabolized by beta-oxidation (a pathway that breaks down fatty acids into acetyl-CoA), producing ATP, NADH, FADH2, and H+. Acetyl-CoA then enters either the citric acid cycle or ketogenesis (a pathway that produces ketone bodies from acetyl-CoA). Ketone bodies are acidic compounds that can be used as an alternative source of energy by some tissues such as the brain and heart when glucose is scarce.
Amino acids
– Amino acids are organic compounds that contain an amino group (-NH2) and a carboxyl group (-COOH).
– Amino acids are the building blocks of proteins, which are essential for the structure and function of cells. Amino acids are obtained from the digestion of proteins in food or from the breakdown of proteins in muscles and other tissues.
– Amino acids are transported by the blood to various tissues where they are metabolized by transamination (a reaction that transfers an amino group from one amino acid to another), deamination (a reaction that removes an amino group from an amino acid), or decarboxylation(a reaction that removes a carboxyl group from an amino acid), producing various metabolites such as pyruvate, acetyl-CoA, oxaloacetate, alpha-ketoglutarate, succinyl-CoA, fumarate, and malate.
– These metabolites can then enter different pathways such as glycolysis, citric acid cycle, gluconeogenesis, or urea cycle (a pathway that converts ammonia into urea for excretion).
Hopefully you now have some first-hand information about metabolism, its types and processes🤗.
