PDBIO 305: Cell Metabolism - Week 2
PDBIO 305: Cell Metabolism - Week 2 PDBIO305
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This 4 page Class Notes was uploaded by Kirsten Notetaker on Friday September 9, 2016. The Class Notes belongs to PDBIO305 at Brigham Young University taught by David Thomson in Fall 2016. Since its upload, it has received 10 views. For similar materials see Human Physiology in Physiology and Developmental Biology at Brigham Young University.
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Date Created: 09/09/16
Metabolism ***FOR EXAM it is most important to know basic concepts along w/ reactants, products & enzymes/cofactors and where things happen – specific intermediate steps are not as important. Make sure to know how much of each product is produced from each step (glycolysis, Krebs/Citric Acid cycle, etc. for a given amount of a certain reactant!*** ATP (Adenosine Triphosphate) – cellular energy currency Made from adenine, ribose & 3 phosphate groups ATP Hydrolysis fun fact: every day you turn over (breakdown & resynthesize) an amount of ATP roughly equivalent to your body weight! Cellular movement, molecular synthesis, & transport across membranes all require ATP Phosphocreatine (PCr) Creatine phosphate + ADP -> creatine k<- creatine + ATP Able to produce ATP very quickly! ATP Production from Glucose: Glycolysis -> Citric acid (Krebs) cycle -> oxidative phosphorylation Glycolysis 10 separate sequential chemical reactions that break down glucose into 2 pyruvate molecules Anaerobic process Occurs in cytosol of cell Not very efficient – low energy yield Glucose -> 2 pyruvate Uses 2 NAD and 2 ADP + 2 P -> 2iNADH + H (to be used in oxidative phosphorylation) and 2 ATP Mitochondria and ATP production Pyruvate converts to acetate -> Acetyl-CoA -> citric acid cycle -> Occurs in mitochondrial matrix Mitochondria Energy organelle Major site of ATP production Contains enzymes for citric acid cycle & e- transport chain Enclosed by a double membrane Linking step Converts pyruvate (3 carbon) to acetyl-CoA (2 carbon) + + Pyruvate + CoA + NAD -> acetyl CoA + CO + NADH2+ H Krebs Cycle For each acetyl-CoA proceeding through the cycle: produces 1 ATP (GTP), 3 NADH, 1 FADH , 2nd 2 CO 2 Does not require molecular oxygen, but will stop if oxygen is not available to the e- transport chain (ETC) Pyruvate from glycolysis is converted to acetyl-CoA which enters citric acid cycle Cycle consists of eight reactions directed by enzymes of mitochondrial matrix Important in preparing hydrogen carrier molecules for entry into ETC Total produced so far (from glycolysis & Krebs cycle): 4 ATP, 10 NADH, 2 FADH2, 6 CO2 Electron Transport Chain (ETC) – mechanism of oxidative phosphorylation NOTE: this is mostly a reference to help understand the overall process, remember you don’t need to memorize each of these reactions Requires oxygen Series of reactions on the inner mitochondrial membrane Major source of ATP 1) H released by earlier rxns is carried to inner mitochondrial membrane by NADH or FADH and released 2 a. NAD is free to pick up another H 2) A “high energy” e- is extracted from the H and passed along from protein to protein, releasing energy as it moves to a lower-energy state 3) This energy is used to pump H (generated in step 2) from the matrix to the intermembrane space a. Creates an electrochemical gradient 4) At end of ETC oxygen recombines w/ H -> H O 2 5) Proton gradient generated in step 3 has stored energy – protons want to travel down from high-energy state in intermembrane space back into the matrix, where energy state is low a. Occurs through a H ion channel called ATP synthase 6) ATP synthase uses energy released as protons flow through it to generate ATP from ADP and inorganic phosphate 7) NADH drops its H and associated e- off at complex I and results in the release of enough energy for production of ~2.5 ATP 8) FADH drops its H and associated e- off at complex II. This is downstream from complex I and thus less energy is released, fewer protons are pumped into the intermembrane space, and fewer ATP (~1.5) are generated Uncoupling proteins (UCPs) insert in the inner-mitochondrial membrane + and act as a channel through which H can be transported Protein & fat are oxidized in similar ways Protein -> amino acids -> Krebs cycle -> oxidative phosphorylation, etc. Fat oxidation Fats are stored as triglycerides (glycerol + 3 fatty acids) Lipolysis = breakdown of triglycerides Fatty acids separate from glycerol Glycerol can enter glycolysis Beta-oxidation = Fatty acids (many carbons) -> acetyl CoAs (2 carbons) This then enters the Krebs cycle -> oxidative phosphorylation, etc. Typical fatty acid is 12-14 carbons in length, so many Acetyl CoAs are produced from 1 fatty acid molecule This occurs in the mitochondria “Anaerobic” Glycolysis Normal glycolysis is actually not ever aerobic (using oxygen), but “anaerobic” glycolysis refers to the glycolysis which happens when oxygen supplies are limited (which affects the ETC) When oxygen is limited, the ETC gets backed up and NADH levels + increase because they can’t enter the ETC -> decrease in NAD levels Decrease in NAD -> Krebs cycle can’t go, so it stops -> buildup of acetyl CoA and pyruvate + Decrease in NAD also -> glycolysis can’t go, so it also stops + Lactate dehydrogenase uses NADH + H to convert pyruvate -> lactate + This converts NADH -> NAD , which can now be used to continue glycolysis This is less efficient because the NAD must be used again for the pyruvate conversion, so it does not go to the Krebs cycle and less ATP is produced – but this process can still happen quickly in response to oxygen deficiency This process is not indefinite, as the pH will decrease (conditions become more acidic) – eventually you will need to begin aerobic glycolysis again, but this helps while oxygen is limited Gluconeogenesis Creation of “new” glucose Amino acids, glycerol, lactate, are used as substrates for glucose formation Basically the reverse of the ATP production process
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