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Lecture 2

Lecture 2 Cellular Metabolism Continued.docx

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Biological Sciences
Jason Brown

Lecture 2 Cellular Metabolism Continued Slide 15 Metabolic Production of ATP Anaerobic Pathways Phosphagens Its not being used up that phosphate group bonded to ATP is immediately transferred to creatine to form phosphocreatine and that helps to keep then the ATP concentration from getting too high in the cell So creatine aside from being a source of ATP when ATP levels get low also plays to store the energy from ATP when ATP levels are getting too high so they keep ATP levels in the cell relatively constant And that allows the cell to know this is how much energy it is going to take to build a new ATP and this is how much energy it is going to take to hydrolyze ATP And if we allow ATP levels to fluctuate sometimes it takes a lot of energy and sometimes little And that is the role of phosphagens Slide 16 Metabolic Production of ATP Anaerobic Pathways PhosphagensOn the right hand side it is supposed to be a muscle the mitochondrion in the muscle cells are using ATP and at that site where ATP is being used up and the ATP levels at that area drop the phosphate group fromthe phosphocreatine gets converted back to creatine to regenerate ATP So two roles of phosphagens theyre basically a store house for energy of ATP and also regulate the ATP levels from getting too high in the cell Slide 17 Metabolic Production of ATP Anaerobic Pathways Adenylate Kinase Heres another anaerobic pathway for the generation of ATP it involves two enzymes it requires this reaction ATP plus AMP2 ADP AMP is just ATP with only one phosphate group adenosine monophosphate Their structures look the same but just different number of phosphates We can initially take two ADP molecules and we build them together to make one ATP molecule and one AMP molecule In the cell this reaction is at equilibrium so it is able to shift back and forth What happens in the cell as we use ATP and generate ADP how do we make this reaction go the direction we want to which is to take the 2 ADP and make it back into ATP All we have to do is get rid of AMP If we degenerate the AMP concentration this reaction will shift to the left it will try to make more AMP to replace what has been lost and in the process it will produce ATP We have another enzyme AMP dianamase this is the enzyme that takes the molecule of AMP and loses the oxygen and nitrogen from it as a waste product essentially AMP dianamase as its name suggests strips the amine group off the AMP to the left and it will not only regenerate AMP but also ATP in the process This reaction shows how to produce ATP without oxygen This reaction however also gets rid of basic molecules you need to bring ATP back up You cannot run this cycle indefinitely because as you keep degrading AMP eventually you are going to run out of the substrate you need to rebuild that ATP So if you are going to degrade all of AMP eventually you are going to run out of substrates to build ATP short term solutionSlide 18 Metabolic Production of ATP Anaerobic Pathways Glycolysis Another pathway is glycolysis There are nine steps in this pathway Initially reaction 1 and 3 these two reactions actually use up cellular ATP and these are the energy investment phases of glycolysis So these two early reactions consume ATP and they do so to regenerate phosphorylate compound In reaction one we use an ATP molecule to add a phosphate group to glucose to get glucose6phosphate than in reaction 3 we add another phosphate group using ATP to generate fructose 1 6 diphosphate so early stages of glycolysis the focus is on using ATP to build these phosphorylated sugar molecules The really important reaction in glycolysis is number 5 The conversion of glyceraldehyde to glycerate which is a carboxylic acid aldehydecarboxylic acid the amount of energy that is released is sufficient to do two things
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