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module 16 - metabolism.docx

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Physiology 2130
Ingrid L.Stefanovic

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Module 16 – Metabolism Intro  Fats, carbs, and proteins are used for energy or to build structures  Metabolism - chemical changes that occur within a cell to either manufacture energy, store energy, or build new cell structures o Anabolism – creation of large molecules from small ones with the use of energy (ATP) o Catabolism – breakdown of large molecules  small ones resulting in the release of energy (ATP) Building Blocks  Triglycerides which make up most of the fat found in the body consist of 3 fatty acid chains attached to one molecule of glycerol  Proteins = long chains of AA linked tg  Carbs = long chains of monosaccharides (like glucose) joined tg  These building blocks are circulating in the body and can be used to create new structures in the cell or to form ATP, or they can be stored for later use o Their storage form may not be the same as their circulating form  The carb glucose is stored as glycogen inside muscle and liver cells  Fats are stored as triglyercides inside fatty (adipose) tissue  AA become structural or functional proteins inside the muscle cells Building Blocks – Energy Production  Glucose = 1% of the total energy requirements of the body and its reserves (in the form of glycogen) can last for a day  Fatty acids = 77% of the total energy produced and can last up to 2 months depending on the individual  AA stored as proteins are not usually used to create energy but can account for 22% of the body’s fuel requirements if absolutely necessary Metabolism – A General Look  3 primary chemical rxns that take place within the cell to produce energy from the breakdown of food molecules o Glycolysis (glycolytic pathway)  Series of rxns that occurs in the cytoplasm  Works very rapidly  Does not require O2 and is therefore an anaerobic rxn  Can produce 2 molecules of ATP very quickly from 1 molecule of glucose o Citric Acid Cycle (CAC/Krebs Cycle)  Takes place inside the mitochondria  Works slowly  Requires the presence of O2 and is therefore an aerobic rxn  Can produce 2 molecules of ATP per molecule of glucose o Oxidative phosphorylation (Electron Transport Chain)  Closely linked to the CAC  Can produce 34 molecules of ATP from 1 molecule of glucose  Occurs in the mitochondria and also requires O2  Each of the food molecules can enter 1 or more of these rxns to make energy (ATP)  Example: o Glucose/glycogen can enter glycolysis at the beginning of this rxn o AA can be converted to pyruvate to enter glycolysis or can be converted to acetyl coenzyme A (acetyl CoA) to enter the CAC to produce ATP o Fats (triglycerides) can be broken down to glycerol and free fatty acids  Glycerol molecules can enter glycolysis  Fatty acids can be converted to acetyl CoA to enter the CAC Metabolism of Glucose  Glucose = monosaccharide and is stored as glycogen in most cells of the body  However, most glycogen stores can be found in the liver and skeletal muscle  Glucose is a common fuel source for all cells in the body, but it is one of the only fuel sources for the brain – unlike most other cells in the body, which can use fats and AA as well as glucose  The liver stores glucose for the brain, which cannot store any for when blood glucose levels get low Metabolism of Glucose – Glycolysis  Glucose will enter a cell and will be almost immediately converted to glucose-6-phosphate (G-6-P)  From here G-6-P can enter glycolysis to produce ATP or it can be converted to glycogen and then stored  When necessary, glycogen can be converted back to G-6-P to enter glycolysis to produce energy  In glycolysis, G-6-P will undergo a series of rxns that will result in the production of ATP and the end product of pyruvate o The pyruvate can then undergo 2 possible rxns:  Enter the CAC and produce lots of ATP with the help of oxidative phosphorylation  Enter another shorter rxn to produce a small amount of ATP and the by-product lactate (lactic acid) o Which rxn will pyruvate take?  Depend on whether O2 is present or not  If there is sufficient O2 then most of the pyruvate will enter the CAC  CAC is an aerobic pathway, it requires O2  If there is not enough O2 present, then the CAC will not be running at full capacity and the pyruvate will be converted to lactic actid Metabolism of Glucose – Lactic Acid  During strenuous exercise, you CV system may be able to supply sufficient O2 to your working muscles to produce ATP via CAC o However, since glycolysis is anaerobic, this rxn can continue without O2 to produce ATP and the end product pyruvate o With insufficient O2, the CAC will not work at full capacity and pyruvate will start to accumulate o If too much pyruvate accumulates, then even glycolysis will be slowed o In order to keep glycolysis working so it can produce ATP for the muscles, the pyruvate will be converted to lactic acid  The accumulation of lactic acid causes the ‘burning’ sensation in the muscle and is believed to interfere with the contractile proteins causing fatigue o The accumulation of lactic acid will cause the blood vessels to dilate and the decreasing pH will unload more O2 from hemoglobin o These mechanisms will help to increase blood flow and increase O2 delivery to this working tissue to reduce the buildup of lactic acid  Important to note that most of the rxns we’ve seen is reversible (can work in both direction) o Ie. if O2 is restored, lactic acid can be converted back to pyruvate to enter the CAC o Also, pyruvate can be turned back into glycogen, through G-6-P and stored for later use Metabolic of Glucose – CAC  If there is a sufficient supply of O2, then the CAC can function at full capacity  The pyruvate from glycolysis is converted to acetyl CoA, which then enters the CAC o The CAC in conjunction with oxidative phosphorylation together produce a total of 36 molecules of ATP from 1 molecule of glucose (2 ATP from CAC and 34 from oxidative phosphorylation) o They also produce by-products CO2 and H2O  The CO2 will diffuse into the blood and leaves the body at the lungs Metabolism of Glucose – Review  Glucose enters the cells where it can be converted to its storage form of glycogen, or it can enter the glycolytic pathways where it will produce ATP and pyruvate  Without sufficient O2, the pyruvate will be converted to lactic acid wile producing ATP  In the presence of O2, the pyruvate will enter the CAC to produce large quantities of ATP while giving of
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