Chapter24.pdf EXSC 223 001
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This 0 page Class Notes was uploaded by Chase Heffron on Tuesday December 8, 2015. The Class Notes belongs to EXSC 223 001 at University of South Carolina taught by Thompson in Summer 2015. Since its upload, it has received 29 views. For similar materials see Anatomy and Physiology 1 in Physical Education at University of South Carolina.
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Date Created: 12/08/15
Chapter 24 Metabolism biochemical reactions within cells involving nutrients either making something or breaking something down These reactions can include two subcategories Anabolism synthesis of large molecules from small ones amino acids proteins glucose glycogen Catabolism breakdown of complex structure to simpler ones Cellular respiration this is aerobic metabolism We start off with a glucose molecule and it reacts with oxygen We break down the glucose to c02 and h20 This is the catabolic part of cellular respiration During this reaction ATP is formed by the synthesis of ADP and an inorganic phosphate This is the anabolic part of the reaction Often times we will break down an ATP molecule and attach the phosphate group to a protein This changes the proteins shape A number of enzymes are regulated by phosphorylating or dephosphorylating them Regulation involves energy 3 energy storing macronutrients are amino acids glucose and triglycerides From here amino acids can be used to produce proteins sugars can be stored as glycogen We are going to talk extensively about glycolysis Oxidationreduction reactions redux oxidation is gain of 02 or loss of H and e Rust is an oxidation reaction Reduction gain of H and e or loss of 02 There are enzymes responsible for transfer of hydrogens or electrons Dehydrogenase removes hydrogens Oxygenase transfers oxygen Coenzymes act as hydrogen or electron acceptors Usually these molecules remove or add hydrogens to NAD and FAD NAD and FAD are based on two different B vitamins ATP synthesis two ways the rst is known as substrate level phosphorylation This is an enzymatic reaction An enzyme takes ADP and a phosphate and creates ATP This is responsible for only a small amount of ATP produced The other way is oxidative phosbhorvlation Here a hydrogen gradient is produced ATP synthase harnesses this potential energy and allows hydrogens to move down the gradient and takes ADP and Pi and puts them together to make ATP Glycolysis can be anaerobic or aerobic Anaerobic breakdown of glucose C6H1206 heat D 6C3H603 2 ATP This process is self limiting but rapid In oxidation of glucose more ATP is produced C6H1206 602 D 6H20 6C02 32 ATP heat This is a much slower process This is partially because it involves two additional pathways Glycolysis takes place in the cytosol Glut transporter of glucose across membrane 2 dary active transport Needs a sodium gradient to move glucose into the cell Glucose is transported across the membrane Glucose is tagged with a phosphate on carbon 6 by hexokinase This uses ATP This way glucose cannot leave the cell This is because most cells cannot dephosphorylate glucose Next the rst carbon on glucose is tagged with an inorganic phosphate by Dh05phofructokinase This uses an ATP Using these ATPs are an investment to produce more energy PFK is the slowest enzyme in the glycolysis process Glycolysis only proceeds as fast as PFK does These rst two steps are the investment phase Next is the cleavage phase The 6 carbon and 2 phosphate molecule is split into two glucose 3 phosphate molecules One of the molecules has a phosphate on the rst carbon the other has a phosphate on the 3rd The enzyme can only work on the one with the phosphate on the 3rCI carbon So the molecule with the carbon on the rst gets converted to match the other molecule Next a dehydrogenase takes a hydrogen from these molecules and gives It to NAD to make it NADHH In the next two steps phosphates are taken from the carbon molecules and bound to ADP to make ATP 4 ATP are produced In glycolysis you produce a total of 4 ATP That is the gross ATP production The Net atp production is 2 ATP 2 ATP were invested to produce 4 Glycolysis cannot continue without NAD There is a mechanism in place to recycle NAD There are two processes to how NAD is recycled At the end you are left with 2 pyruvate molecules Recycling of NAD is essential What happens is that NADH comes down and donates hydrogens and electrons to the pyruvate molecule Lactate dehvdrooenase transfers hydrogens off of the NADH molecule to the pyruvate to make it a lactate molecule The advantage to this is it recycles the NAD molecule This recycling permits glycolysis to continue Monday There are 2 ways to recycle NAD Lactic acid the production of lactate in the cells that process is anaerobic The other way is in the electron transport chain Pyruvate is transported into mitochondria In the process of getting inside the cristae of the mitochondria C02 is released and 2 hydrogens and electrons are released into the mitochondria and the new molecule produced is called acetyl CoA This is not part of the krebs cycle it is an intermediate step Red skeletal muscles the heart this process above is likely to happen In white skeletal muscles you39re more likely to produce lactic acid Krebs cycle Acetyl CoA 2C oxaloacetate 4C is formed into citrate by citrate synthase 6C The products of krebs cycle for one single round 3 NADHH 1 FADH2 1 ATP Electron transport chain When electrons pass through complex 1 hydrogen gets pulled into the intermembrane space The electron passes through 3 complexes and powers these complexes to pump out a hydrogen atom to the intermembrane space The hydrogens getting pumped through the pumps are free oating hydrogens in the matrix Wednesday Pvruvate dehvdrooenase allows pyruvate to get into the mitochondria during the intermediate step between glycolysis and the krebs cycle For every acetyl CoA one ATP 3 NADHH and 1 FADH2 Electron transport chain The Complex l is a dehydrogenase lt strips NADHH of its hydrogens and they are thrown into the matrix The electron released from this causes Complex l to change shape and allow for the movement of hydrogens into the intermembrane space The electron travels down to Complex Ill and Complex IV and powers these complexes to pump hydrogen For every electron donated by NADH 3 electrons are pumped into this intermembrane space This pumping of hydrogens creates a gradient that powers the synthesis of ATP ATP Synthase which is found on the matrix membrane allows for hydrogens to go down there gradient into the matrix For every hydrogen that passes through ATP synthase 1 ATP is produced This whole process is called oxidative phosphorylation Complex II is underneath complex I This is where FADH2 loses its hydrogens and electrons The electron that it donates passes through Complex Ill and complex IV so it only allows two hydrogens to pass through the matrix membrane Oxygen is the nal electron acceptor Oxygen must be present at the end of oxidative phosphorylation to accept electrons inside complex 4 If not the gradient will become weaker and stop the ow of protons into the matrix 02 4H 4e l 2H20 NADHH 25 ATP atp is expended shuttling NADH into the matrix FADH2 15 ATP ln glycolysis 2 ATP are invested We produce 4 ATP from glycolysis So net ATP is 2 2 NADH are produced in glycolysis 2 pyruvate l 2 acetyl CoA This transition process produces 2 NADH In the krebs cycle 3 NADH are produced from one acetyl CoA molecule 1FADH molecule is produced 1 ATP is produced from substrate level phosphorylation Multiply all these by two because 2 acetyl coA molecules go through the krebs cycle for every glucose molecule 34 gross ATP net about 32 ATP FHday Lipid metabolism majority of atp produced actually comes from lipids not glucose This is the breakdown of the storage form of fat Oils are triglycerides Your body cannot absorb triglycerides so we break them down into their components They are made up of glycerol and fatty acids Glycerol is a 3 carbon molecule Fatty acids are long carbon chains Unsaturated vs saturated is referring to the double bonds in fatty acids One double bond is monounsaturated Polyunsaturated is multiple double bonds When we breakdown triglyceride glycerol can enter glycolysis at the step with glyceraldehyde 3 phosphate Beta oxidation this is where the fatty acids go to This is a process where two carbons are cleaved off at a time from fatty acids The nal product of beta oxidation is acetyl CoA which can then go through the krebs cycle BO also strips off electrons and produces 1 NADHH and 1 FADH2 This occurs in the mitochondria Different energy sources have different energy values Carbs have about 4 kilocalories Protein also has an energy value similar to Carbs about 4 Lipids can produce about 9 kilocalories from fats Lipids are a much more dense form of energy storage lecooenesis dlvcooen is the storage form of glucose Glycogen is stored primarily in skeletal muscle and the liver Glycogen is produced from glycogen synthase Glycogen is highly branched The branching allows it to store more and more glucose We store lots of water with glycogen Glucose is brought in to the cell and converted to glucose 6 phosphate From here it can either go to glycolysis or the phosphate can be moved to the rst carbon Then this molecule is added to glycogen by glycogen synthase Glycogenolysis this is the breakdown of glycogen via glycogen phosphorylase in response to high energy demand or low blood sugar Glycogen phosphorylase can take a glycogen molecule and add a phosphate to the 1St carbon then from there it can be converted to glucose 6 phosphate ln skeletal muscle when glycogen is broken down you convert it to glucose 6 phosphate and let it go through glycolysis In the liver you convert it to glucose 6 phosphate and release it into the blood This is what allows you to maintain blood glucose between meals Without glucose and glycogen muscle cell have a hard time producing ATP They can use fats but they need glucose Normal blood glucose level 100 mgd When blood glucose goes up it triggers a set of events The pancreas secretes a hormone called insulin The beta cells of pancreatic islets produce this These cells are sensitive to glucose levels When glucose levels are high they produce insulin Almost every cell in the body has insulin receptors lnsulin facilitates the diffusion of glucose into the cell Glucose passes through the protein glut into the cell The glucose can be used for energy stored as glycogen or stored as fat Insulin is under negative feedback regulation Absorptive state when you eat a meal you are absorbing nutrients so you are in the absorptive state lnsulin is usually released in this state lnsulin also promotes protein synthesis The postabsorptive state or fasting state is between meals This state is entered once bgl comes back to normal levels We remain in this state until eating again Sitting here right now your brain uses the most glucose The liver plays a crucial role in regulating bgl in this state The liver stores lots of glycogen We can release glycogen into the blood stream Your brain only uses glucose There is a hormone to help break down glycogen This hormone also breaks down triglycerides This is known as glucagon It is secreted during this post absorptive phase Glucagon is produced in the pancreas right next to the cells that produce insulin It is produced by alpha islet cells They can detect low bgl It is released by blood sugar is low and the glucagon goes to the liver to break down glycogen This is also under negative feedback control Glucagon is secreted when you fast to maintain bgl Our body has the capacity to synthesize glucose Gluconeogenesis is the formation of glucose molecule from nonglucose sources This is known as the glucose alanine cycle Glucose can be converted to pyruvate in and in some cases pyruvate can be converted to alanine in muscle cells Alanine can go to the liver and can be converted back to pyruvate and eventually glucose When people are starving the body does this to a large degree We can also break down proteins to convert to glucose Transamination is the rst step In the liver a keto acid is added to an amino acid that will be used for energy The nitrogen group keto acid is transferred and a new amino acid glutamic acid is produced Oxidative deamination is the next step The glutamic acid is oxidized which produces ammonia which is a toxic substance The ammonia mixes with C02 to form urea Urea is later excreted out in urine The 3rd step is keto acid modi cation The modi ed keto acid can enter the bloodstream and go to cells These keto acids can enter the krebs cycle and get used for energy This also can happen after eating a high protein meal because we cannot store proteins Lipogenesis is the formation of new lipids We store lipids as triglycerides These are a rich source of energy Glucose can be converted to fats easily but fat is a little more dif cult We can break down triglycerides This is called lipolysis They must be broken down to be transported across cells The glycerol molecule can be modi ed to glyceraldehyde 3 phosphate and enter glycolysis The Fatty acids enter Beta oxidation and can be converted into acetyl CoA Our bodies cannot convert acetyl CoA to pyruvic acid This means that fatty acids cannot directly synthesize glucose However glycerol can be used to produce glucose A few things can happen to Acetyl CoA It can enter the krebs cycle It can also be used in the production of cholesterol Ketone bodies can also be produced You only see these produced when your body perceives that it is starving Ketone bodies can be used by neurons in the brain as a temporary energy source until you get enough glucose When someone39s blood ph falls they tend to hyperventilate and there is a distinctive odor This is called ketoacidosis Acetyl CoA can also be converted to fatty acids
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