Overview of Metabolism: Anabolism & Catabolism

Overview of Metabolism Overview of Metabolism: Anabolism & Catabolism: Metabolism is a series of chemical reactions that take place within our bodies in order to sustain life and our ability to maintain four macromolecules (proteins, lipids, nucleic acids, and carbohydrates) We obtain a lot of these through food and digestion by breaking it down into whatever we may need In other words, metabolism is a balance between breaking things down into their individual components/monomers (catabolism) and building them back up into things like polymers (anabolism) Anabolism takes energy in order to accomplish and can be coupled with ATP hydrolysis in order to drive these sorts of processes (catabolism makes ATP through processes like cellular respiration and anabolism uses it) Hormones are a method of control for whether the body should be in a catabolic or anabolic state “Catabolism fuels anabolism” ATP: Adenosine Triphosphate: Often referred to as the “energy currency” of life The bonds between the phosphate groups are high energy because of their repulsive nature (negative phosphate groups stacked right next to one another) The most amount of energy is located between the gamma and beta phosphate groups on ATP ATP Hydrolysis: Gibbs Free Energy: 𝛥𝐺 = 𝛥𝐺𝑃 − 𝛥𝐺𝑅 (If negative, then it is exergonic and if positive, then it is endergonic) ATP + H2O → ADP + Pi has a very negative 𝛥𝐺 value releasing a lot of energy Many other reactions have a positive 𝛥𝐺 value which is coupled with the exergonic reaction of ATP hydrolysis (shown above) Remember, the overall 𝛥𝐺 can be shown by adding up all of the individual 𝛥𝐺 values from the reaction scheme We simply hope that the ATP hydrolysis has more energy than the other reaction needs on its own Also, adding up the 𝛥𝐺 tells you nothing about the path traveled, just simply showing that an energetically unfavorable process can become favorable through reaction coupling ATP Hydrolysis: Transfer of a Phosphate Group: A lot of the times, ATP donates its phosphate group to the reactants, giving a 𝛥𝐺>0, which wouldn’t drive the reaction on it’s own. It is typically the second step of the reaction that would push the reaction forward (this can be seen in the formation of DNA from individual nucleotides depicted to the right → hydroxyl groups replaced the stacked phosphate groups that hate being next to one another) It is the final step where Pi is broken down into individual units, and using Le Chatelier’s Principle this drive the reaction to the right ATP has a very high activation energy and therefore doesn’t just phosphorylate whatever it wants and therefore using enzymes in order to selectively phosphorylate things Oxidation-Reduction Review from Biological Point-of-View: Oxidation is losing electrons (OIL) and Reduction is gaining electrons (RIG) Oxidation is called this because you typically lose electrons to oxygen Elements bonded to one another share electrons equally and therefore have a neutral oxidation state (such as H2 or O2) However, with water (H2O) the electrons are not shared equally, oxygen likes to hog the electrons For oxidation states you assume that the atom completely took the electrons (even though that didn’t technically happen) and therefore in water oxygen has an oxidation state of -2 (since it “gained” 2 electrons) and each hydrogen have an oxidation state of -1 (since it “lost” 1 electron each) In the biological point-of-view electrons are exchanged using hydrogen meaning that they come paired with one another This means that when hydrogen bonds to most things, it tends to give up its electron since most other elements are more electronegative Oxidation & Reduction in Metabolism: Species gaining electrons are being reduced and species losing electrons are being oxidized The overall reaction of cellular respiration is: C6H12O6 + 6O2 → 6H2O + 6CO2 This reaction is also a redox reaction (O2 is reduced while glucose is oxidized) In metabolism it’s basically just a flow of electrons in order to form ATP Each step of oxidation for glucose, they form products that are more and more oxidized, donating electrons to electron carriers that directly donate electrons into the electron transport chain (ETC) Electron Carrier Molecules: Electron carrier molecules come through to donate electrons to the ETC Since glucose is oxidized to CO2 then the electron must go somewhere, which is where the electron carriers come into play The oxidation of glucose takes place in several steps known as cellular respiration Metabolite is just a name for whatever molecule is spit out at each step of cellular respiration (such as pyruvate, acetyl-CoA, etc) The breakdown of glucose is simply another example of combustion (which is a reaction where the products are H2O and CO2 and reactances are a fuel and O2) If glucose simply combusted, energy would not be able to be harnessed by the body The EA needed in order to combust a sugar such as glucose is extremely high The high EA is overcome by the use of enzymes Enzymes also allow a controlled manner as opposed to a big burst of energy released from a single step combustion process Electron carriers are also called coenzymes (a molecule/chemical functional unit that helps the enzyme do its job) Most enzymes involved are known as dehydrogenases (they dehydrogenase glucose and therefore take away 2 electrons per proton → Hydride ion) NAD+ and FAD both are electron carriers (note that FAD does not have a positive charge in its oxidized state) ATP Hydrolysis Mechanism: Also releases energy (should be added in as a product) Notes: Remember, cleaving a bond always requires energy input Entropy will typically increase if the products are more numerous than the reactant The spontaneity of a reaction can be changed by altering the equilibrium Q which is the ratio of products to reactants