# Metabolism --- **Metabolism** is the sum of all [[chemical reaction|chemical reactions]] that take place in our body. We, as in all life, are metabolizing 100% of the time. The building blocks of life, the [[macromolecules]] and other [[nutrients]] are being constantly built and constantly harvested. Harnessing metabolism and controlling its flow has been the single most important event in the [[evolution]] of life. The map below is a representation of every [[#Metabolic Pathways|metabolic pathway]] that humans undergo. Each dot is a reactant or product and each line between them is a different reaction. ![[metabolism map.png]] The central blue line that ends in a circle is [[glycolysis]] and the [[citric acid cycle]], whose prominence illustrates their importance to all of life. ## Metabolic Pathways A **metabolic pathway** is a series of connected chemical reactions that feed one another. Everything in biology is going from substrate to product to substrate to product, but in these metabolic pathways this process happens very quickly. They are incredibly intricate and complicated process, often requiring many critical [[enzyme|enzymes]]. ### Anabolic & Catabolic Reactions Metabolic pathways either break down large molecules during [[catabolism]] or build up smaller molecules *into* those large molecules during [[anabolism]]. Cells can harvest energy when they are storing away their building blocks, then use that energy later to build up larger structures. ![[catabolism and anabolism.png]] ### Energetic Coupling Because a lot of these anabolic reactions are really expensive, most reactions are [[endergonic and exergonic#Energetic Coupling|coupled]] such that reactions that *produce* energy are combined with those that *cost* energy. By doing so, this makes the pathways as efficient as possible. Often times enzymes are even coupled next to each other in such a way that they can pass along their products directly to the next enzyme in the pathway. ## Types of Metabolizers In order to classify different organisms by what they metabolize, first we must establish the four things all organisms need to survive: - A **source** of **electrons** (or in other words, and [[biological energy|energy source]]) - A **recipient** for those **electrons** (which is as a rule, highly [[electronegativity|electronegative]]) - A **source** of [[carbon]] with which they can build their own things - A **source** of **other essential** [[nutrients#Micronutrients Vitamins Minerals|miscellaneous molecules]] like N, S, and P to use for building blocks, and Fe and Mg for [[cofactor|cofactors]] for enzymes. We can then classify organisms based on those first three traits, and as every organism needs all three aspects, the classifications can and are mixed and matched. The one exception is that phototrophs are almost always autotrophs as well. Classifications can be further refined as well, such as respirators being able to be aerobic or anaerobic. ### Chart Uses a/n... | ...as an electron source: | ...as an electron acceptor: | ...as a carbon source: --------------------------|-----------------------------|------------------------------------|-------------- ...**organic molecule**... |chemoorganotroph |[[fermentation\|fermentator]] |heterotroph ...**inorganic molecule**...|[[chemolithotroph]] |[[cellular respiration\|respirator]]|autotroph ...**molecule energized by light**...|phototroph | (N/A) | (N/A) ## Metabolic Homeostasis Metabolism comprises thousands of different chemical reactions, yet the amounts and identities of molecules inside cells are relatively constant. By regulating key reactions involved in catabolic and anabolic pathways, the cell is able to maintain [[homeostasis]] even under different environmental conditions. The [[thyroid]] is a big regulator of metabolism, particularly with the release of [[thyroid hormone]]. **Hypometabolism** - Slow HR/lower BP - Weight gain - Flat, dull affect, sluggish - Cold intolerance - Constipation **Hypermetabolism** - Fast HR/higher BP - Weight loss - Irritable, hyperactive - Heat intolerance - Increased motility, diarrhea ## Sugar Can Be Metabolized Into *Any* Amino Acid (But Not By Us) Technically any amino acids that you need you could built from scratch. A lot of [[bacteria]] can do just that that. But humans can only synthesize about half of them, because we have gotten so good at hunting food, growing food, otherwise gaining the necessary amino acids from other means, and have simply lost the ability. These are the [[essential and non-essential amino acids|essential amino acids]]. ___