UB BIO 205 - Exam 4 Study Guide (13 pages)

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Exam 4 Study Guide

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Exam 4 Study Guide


This study guide outlines chapters 23 through 28, and includes relevant figures regarding sugar metabolism.

Study Guide
University at Buffalo, The State University of New York
Bio 205 - Fund of Bio Chemistry
Fund of Bio Chemistry Documents
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BIO 205 Exam 4 Study Guide Chapters 23 38 Part IV Sugar Metabolism Chapter 23 Introduction to Metabolism Catabolism is the breakdown of molecules into smaller pieces which allows for the storage of energy in high energy compounds ATP Anabolism involves using ATP to synthesize large macromolecules Important intermediates of glucose metabolism Low energy High energy CoA Ac CoA NAD NAD H FAD FAD H2 ADP ATP Overall map of glucose metabolism 1 Glycolysis glucose is cut in half and converted into two molecules of pyruvate 2 Dehydrogenation and decarboxylation pyruvate dehydrogenase PDH is the enzyme that dehydrogenates pyruvate Pyruvate also loses one carbon CO 2 and attaches to CoA as an acetyl group Pyruvate CoA acetyl CoA CO2 3 Krebs cycle the basic function of this cycle is to convert the acetyl group into two carbon dioxide molecules and store energy in the form of NADH and FADH 2 4 Electron transport NADH and FADH2 pass their electrons to a series of proteins embedded in the inner mitochondrial membrane The flow of electrons creates an H gradient and they eventually join with oxygen to form water 5 ATP synthesis the H gradient flows through ATP synthase creating ATP 6 Beta oxidation fatty acids can be used to create acetyl molecules that are joined with CoA 7 Fermentation when oxygen is not present an organism will perform anaerobic metabolism In animals pyruvate is turned into lactate whereas yeast cells create ethanol and carbon dioxide Anaerobic metabolism only produces 2 ATP which is very small compared to the 38 ATP produced by aerobic metabolism 8 Gluconeogenesis two molecules of pyruvate can be converted back to glucose 9 Urea cycle amino acids and nucleic acids can be incorporated into the Krebs cycle to produce ATP The nitrogen from these molecules is excreted as urea 10 Fatty acid synthesis just as acetyl molecules can be taken from fatty acids and given to CoA acetyl molecules can also be taken from CoA and used to make fatty acid chains 11 Glycogen storage food storage polymers of glucose starch and glycogen can be processed by pathways that link them to glycolysis Beta oxidation is named so because the acetyl group is cleaved at the beta carbon of the fatty acid chain The first step in beta oxidation is a condensation reaction that links CoA to the carboxyl group of a fatty acid Next the beta carbon 2nd carbon from carboxyl carbon is oxidized to a ketone Then the two end carbons carboxyl and alpha are cut off to form acetyl CoA while another CoA molecule attaches to the beta carbon which becomes the new carboxyl carbon The process then repeats until the fatty acid has been broken down When pyruvate is decarboxylized and dehydrogenated it forms acetyl carbon dioxide and NADH Acetyl and carbon dioxide come from the separation of the three carbons in pyruvate NADH is formed from reduction of NAD by the hydride ion from dehydrogenation of pyruvate The Krebs cycle also TCA of citric acid cycle begins by combining acetyl CoA 2C with oxaloacetate 4C to form citric acid 6C Throughout the rest of the cycle two carbon dioxide molecules are formed ergo reforming oxaloacetate keep in mind that one molecule of pyruvate leads to the production of 3 CO2 one from PDH and two from Krebs cycle Furthermore the Krebs cycle produces 3 NADH 1 FADH 2 and 1 ATP first is GTP but is immediately converted The Krebs cycle both receives and provides small carbon skeletons Amino acids can be used to make ATP or parts of the Krebs cycle can be used to make amino acids Different intermediates form different amino acids and vice versa NAD NADH oxidation and reduction NAD is aromatic while NADH is not Therefore NAD is the preferred form due to resonance stabilization and as a result moving from NADH to NAD releases a lot of energy When NADH reaches the mitochondria it gives its electrons to complex I The electrons then travel to complex III then complex IV and finally meet with oxygen and hydrogen to form water FADH2 gives it electrons to complex II which then continues to complex III and so on NADH NAD H 2e2e 2H O2 H2O ATP and acetyl CoA have favorable free energy values of 7 and 8 kcal mol respectively On the other hand NADH and FADH2 both have free energy values close to 50 kcal mol Each NADH produces approximately 3 ATP while FADH2 produces 2 ATP Factors that favor ATP hydrolysis 1 Decrease in repulsion between negatively charged phosphate groups 2 Increased resonance stabilization on phosphate 3 Increased solubility in water due to neutral pKa of hydrogen ATP is thermodynamically unstable but kinetically stable In other words ATP would like to separate into ADP and Pi but the energy barrier is so large that without a catalyst the reaction takes years In a carboxylic acid there are extended pi cloud interactions between the carbonyl oxygen the carbonyl carbon and the alcohol oxygen Although acetyl CoA has a very similar structure and sulfur is right below oxygen in the periodic stable the p orbitals of sulfur are much larger than those of oxygen therefore disrupting the pi cloud in acetylCoA Going back to thermodynamics the bond energy of a reaction can be calculated by subtracting the energy of the reactants from the products A larger bond energy meant that the reaction was favorable Furthermore calculations revealed that polar molecules are more stable than nonpolar molecules When looking at keto enol tautomerization the bond energy of the keto form is slightly higher than the bond energy of the enol form making the keto form the more stable of the two Brown fat found in newborns and hibernating animals contains a protein called thermogenin This protein is able to form a channel through the inner membrane of the mitochondria allowing H to flows down its gradient without producing ATP However the movement of the protons produces heat which keeps newborns and hibernating animals warm In addition to being used for DNA formation pyrophosphate and its irreversible hydrolysis also drives the farnesylation of proteins to produce a nonpolar anchor Another irreversible reaction is the formation of carbon dioxide because it is entropically favored The PDH reaction and two reactions in the Krebs cycle are irreversible because they result in the release of carbon dioxide Summary of favorable processes 1 Separation of like charges 2 Increased resonance 3 Creation of new ionizable group 4 Rearrangement of nonpolar bonds to polar bonds enol keto 5 Dissipation of a gradient 6 Release of pyrophosphate 7

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