Harvesting stored energyGlucose is the modelcatabolism of glucose to produce ATPCO2 + H2O + heatRESPIRATION = making ATP (& some heat) by burning fuels in many small stepsCO2 + H2O + ATP (+ heat)enzymesATP
How do we harvest energy from fuels?Digest large molecules into smaller onesbreak bonds & move electrons from one molecule to anotheras electrons move they carry energy with themthat energy is stored in another bond, released as heat or harvested to make ATPe-+loses e-gains e-oxidizedreducedredoxe-
How do we move electrons in biology?Moving electrons in living systemselectrons cannot move alone in cellselectrons move as part of H atommove H = move electronsoxidationreductione-
Coupling oxidation & reductionREDOX reactions in respiration strip off electrons from C-H bonds by removing H atomsC6H12O6 CO2 = the fuel has been oxidizedelectrons attracted to more electronegative atomsin biology, the most electronegative atom? O2 H2O = oxygen has been reducedcouple REDOX reactions & use the released energy to synthesize ATPO
Energy TransferSubstrate level phosphorylation Oxidative phosphorylation
Substrate Level PhosphyralationATP is formed directly in an enzyme-catalyzed reactionPhosphate containing group transfers a phosphate directly to ADP30.5 kJ/mol of potential energy is also transferred
Substrate Level Phosphorylation1) Occurs in glycolysis & Krebs cycle2) Energy and phosphate are transferred to ADP using an enzyme, to form ATP. 3) PEP (phosphoenolpyruvate) is oxidized. 4) Whereas ADP is reduced. 5) ATP has gained Free Energy from PEP. ATP can now do work.
Oxidative PhosphorylationATP is formed indirectlyInvolves a number of sequential redox reactionsOxygen is the final electron acceptorMore complexMore ATP generated
Moving electrons in respirationElectron carriers move electrons by shuttling H atoms aroundNAD+ NADH (reduced)FAD+2 FADH2 (reduced)NADHcarries electrons as a reduced moleculereducing power!Hlike $$ in the bank
Oxidative Phosphorylation, NAD+Nicotinamide adenine dinucleotide, NAD+CoenzymeVitamin B3Improvements in energy functionsIncreasing NAD+ increases availability of these molecules for metabolismFound in various meats, peanuts and sunflower seeds
Oxidative Phosphorylation, FADFlavin adenine dinucleotide, FADCoenzymeBuilt from riboflavin Vitamin B2Found in meats (liver, kidney & heart), almonds, mushrooms, soybean, green leafy vegetablesAlso reduced by two hydrogen atomsReduced form FADH2In one reaction of the Krebs cycle
NADH and FADH2Act as mobile energy carriersEnergy harvesting reactionsEventually transfer most of their energy to ATP molecules
Oxidative PhosphorylationBegins with nicotinamide adenine dinucleotide (NAD+)Removes 2H atoms from portion of original glucoseElectrons are passed from the NADH to dehydrogenaseNADH becomes oxidized
Oxidative PhosphorylationOccurs in:One reaction of glycolysis During pyruvate oxidation Three reactions of Krebs cycle
Energy TransferGoal is to trap energySubstrate level phosphorylationATP is formed by enzyme catalyzed reaction6 ATP made per glucose moleculeOxidative phosphorylationMany redox reactions form ATP indirectlyMore ATP (30) produced per glucose moleculeForms reduced coenzymes NADH and FADH2 that will eventually transfer their free energy to ATP
Overview of cellular respiration3 metabolic stagesAnaerobic respiration1. Glycolysisrespiration without O2in cytosolAerobic respirationrespiration using O2in mitochondria2. Krebs cycle3. Electron transport chain(+ heat)
Glycolysis and Cancer
2007-2008Cellular Respiration Stage 1: Glycolysis
Glycolysis In the cytosol? Why does that make evolutionary sense?Thats not enough ATP for me!Breaking down glucose glyco lysis (splitting sugar)
ancient pathway which harvests energywhere energy transfer first evolvedtransfer energy from organic molecules to ATPstill is starting point for ALL cellular respirationbut its inefficient generate only 2 ATP for every 1 glucoseoccurs in cytosol
Evolutionary perspectiveProkaryotesfirst cells had no organellesAnaerobic atmospherelife on Earth first evolved without free oxygen (O2) in atmosphereenergy had to be captured from organic molecules in absence of O2Prokaryotes that evolved glycolysis are ancestors of all modern lifeALL cells still utilize glycolysisYou mean were related? Do I have to invite them over for the holidays?Enzymes of glycolysis are well-conserved
10 reactionsconvert glucose (6C) to 2 pyruvate (3C) produces: 4 ATP & 2 NADHconsumes: 2 ATPnet yield: 2 ATP & 2 NADHglucoseC-C-C-C-C-Cfructose-1,6bPP-C-C-C-C-C-C-PDHAPP-C-C-C G3PC-C-C-PpyruvateC-C-COverviewDHAP = dihydroxyacetone phosphateG3P = glyceraldehyde-3-phosphate
Pi364,5ADPNAD+GlucosehexokinasephosphoglucoseisomerasephosphofructokinaseGlyceraldehyde 3-phosphate (G3P)DihydroxyacetonephosphateGlucose 6-phosphateFructose 6-phosphateFructose 1,6-bisphosphateisomeraseglyceraldehyde3-phosphatedehydrogenasealdolase1,3-Bisphosphoglycerate(BPG)1,3-Bisphosphoglycerate(BPG)12ATPADPATPNADHNAD+NADHPiCH2COCH2OHPOCH2OPOCHOHCCH2OPOCHOHCH2OPOCH2OP OPOCH2HCH2OHOCH2POOCH2OHPO1st half of glycolysis (5 reactions)Glucose primingget glucose ready to split
split destabilized glucose
2nd half of glycolysis (5 reactions)Payola! Finally some ATP!78H2O910ADPATP3-Phosphoglycerate(3PG)3-Phosphoglycerate(3PG)2-Phosphoglycerate(2PG)2-Phosphoglycerate(2PG)Phosphoenolpyruvate(PEP)Phosphoenolpyruvate(PEP)PyruvatePyruvatephosphoglyceratekinasephosphoglycero- mutaseenolasepyruvate kinaseADPATPADPATPADPATPH2OCH2OHCH3CH2O-OCPHCHOHO-O-O-CCCCCCPPOOOOOOCH2NAD+NADHNAD+NADHEnergy Harvest G3PC-C-C-PPiPi6 DHAPP-C-C-C
ATP productionG3P pyruvate
Regulation of Glycolysis and Cancer
Glycolysis summary net yield
4 ATPENERGY INVESTMENTENERGY PAYOFF G3PC-C-C-PNET YIELDlike $$ in the bank-2 ATP
Substrate-level PhosphorylationI get it!The Pi came directly from the substrate!In the last steps of glycolysis, where did the P come from to make ATP?ATP
Energy accounting of glycolysis Net gain = some energy investment (-2 ATP)small energy return (4 ATP + 2 NADH)1 6C sugar glucose pyruvate2x6C3CAll that work! And thats all I get?But glucose has so much more to give!
2006-2007Cellular RespirationStage 2:Citric Acid Cycle orKrebs Cycle
Glycolysis is only the startGlycolysis
Pyruvate has more energy to yield
Oxidation of pyruvate3C2C1C
Citric Acid cycle1937 | 1953Hans Krebs1900-1981
citrateacetyl CoACount the carbons!pyruvatex2oxidation of sugarsThis happens twice for each glucose molecule
citrateacetyl CoACount the electron carriers!pyruvatereduction of electron carriersThis happens twice for each glucose moleculex2
Whats the point?
Electron Carriers = Hydrogen CarriersWhats so important about electron carriers? ATPADP + Pi
Energy accounting of Citric Acid cycle Net gain=ATPpyruvate CO23C
Value of Citric Acid cycle?If the yield is only 2 ATP then how was the Citric Acid cycle an adaptation?like $$ in the bank
The Second Law of Thermodynamics states that spontaneous processes tend to increase the entropy (disorder) of the universe. Why would this law favor a glucose molecule being broken down?
The First Law of Thermodynamics states that energy is neither created or destroyed in any process, including chemical reactions. Looking at the big picture of life, and assuming energy used by organisms comes from the sun, how does ATP production by cellular respiration obey the First Law?
*What gets oxidized? What gets reduced? How are photosynthesis and respiration related? Why is it necessary to break down respiration into so many steps? *Last class we saw that the break down of glucose releases a lot of energy. Which is why the breakdown of glucose in the cell occurs through a number of metabolic pathways beginning with glycolysis. What type of reaction is it, anabolic or catabolic? Pay attention to where each of the molecules is coming from and where it is going. If you look at the reaction closely you will notice the movement of hydrogen atoms from glucose to water*So we take in our fuel, food. And we digest into smaller molecules. Through cellular respiration we then break the bonds between the molecules and basically shuffle the electrons around. As the electrons move they carry with them their energy and the energy iis then stored in another bond or released as hear or harvested to make ATP.*Energy is transferred from one molecule to another via redox reactions.
They are called oxidation reactions because it reflects the fact that in biological systems oxygen, which attracts electrons strongly, is the most common electron acceptor. Oxidation & reduction reactions always occur together therefore they are referred to as redox reactions.As electrons move from one atom to another they move farther away from the nucleus of the atom and therefore are at a higher potential energy state.The reduced form of a molecule has a higher level of energy than the oxidized form of a molecule. The ability to store energy in molecules by transferring electrons to them is called reducing power, and is a basic property of living systems.
*C6H12O6 has been oxidized fully == each of the carbons (C) has been cleaved off and all of the hydrogens (H) have been stripped off & transferred to oxygen (O) the most electronegative atom in living systems. This converts O2 into H2O as it is reduced. So which molecule do you think has a higher energy level? The one that is reduced or the one that is oxidized?The reduced form of a molecule has a higher energy state than the oxidized form. The ability of organisms to store energy in molecules by transferring electrons to them is referred to as reducing power. The reduced form of a molecule in a biological system is the molecule which has gained a H atom, hence NAD+ NADH once reduced.soon we will meet the electron carriers NAD & FADH = when they are reduced they now have energy stored in them that can be used to do work.Ultimate goal of respiration is to extract and capture as much of the available free energy as possible in the form of ATP. This is accomplished by two processes substrate level phosphorylation and oxidative phosphorylation*In substrate level phosphorylation ATP is formed directly. Which one the substrate or the ADP is reduced? Which one is oxidized? What about the enzyme? Nothing happens to the enzyme. The enzyme just acts as the catalyst for the reaction to occur. ***Nicotinamide adenine dinucleotide (NAD) and its relative nicotinamide adenine dinucleotide phosphate (NADP) which you will meet in photosynthesis are two of the most important coenzymes in the cell. In cells, most oxidations are accomplished by the removal of hydrogen atoms. Both of these coenzymes play crucial roles in this. Nicotinamide is also known as Vitamin B3 is believed to cause improvements in energy production due to its role as a precursor of NAD (nicotinamide adenosine dinucleotide), an important molecule involved in energy metabolism. Increasing nicotinamide concentrations increase the available NAD molecules that can take part in energy metabolism, thus increasing the amount of energy available in the cell.Vitamin B3 can be found in various meats, peanuts, and sunflower seeds. Nicotinamide is the biologically active form of niacin (also known as nicotinic acid). FAD is built from riboflavin also known as Vitamin B2. Riboflavin is a water-soluble vitamin that is found naturally in organ meats (liver, kidney, and heart) and certain plants such as almonds, mushrooms, whole grain, soybeans, and green leafy vegetables. FAD is a coenzyme critical for the metabolism of carbohydrates, fats, and proteins into energy. Another coenzyme called Flavin adenine dinucleotide performs a function similar to NAD+*Another coenzyme called Flavin adenine dinucleotide performs a function similar to NAD+*Energy harvesting reactionsEventually transfer most of their energy to ATP moleculesAct as mobile energy carriers moving energy from one place to another and from one molecule to another
*Electrons are passed from the electron donor NADH2 to a protein complex (dehydrogenase), the electron donor becomes oxidized into its electron donor form NAD+ while dehydrogenase is reduced. Dehydrogenase uses these electrons to pump protons through the membrane to the outside of the cell. This increasing concentration of protons outside the cell develops a gradient**In most cells glucose is metabolized aerobically in the presence of free oxygen.It is completely oxidized to carbondioxide and water releasing the maximum amount of energy. In some cancers there is not enough oxygen to metabolize the glucose so the cancer cells get most of their energy through glycolysis***Glycolysis literally means breaking of glucose. Glyco lysis. It is a series of 10 reactions in which one glucose molecule is broken down into two pyruvate molecuesl. This is the most universal of all metabolic processs. Occuring eentially the same way in all organisms. Which suggests that it is the most primitive metabolic pathway to have evolved.
Why does it make sense that this happens in the cytosol?Who evolved first?*The enzymes of glycolysis are very similar among all organisms. The genes that code for them are highly conserved.They are a good measure for evolutionary studies. Compare eukaryotes, bacteria & archaea using glycolysis enzymes.Bacteria = 3.5 billion years ago glycolysis in cytosol = doesnt require a membrane-bound organelle O2 = 2.7 billion years ago photosynthetic bacteria / proto-blue-green algaeEukaryotes = 1.5 billion years agomembrane-bound organelles!Processes that all life/organisms share:Protein synthesisGlycolysisDNA replication**Glycolysis is ALWAYS the initial step in the process by which organisms break down sugar to generate fuel for their activities. Two distinct phases: an uphill preparatory phase and a downhill payoff phase.As Figure 4-29 (Glycolysis up close) illustrates, glycolysis is a sequence of chemical reactions (there are ten in all) through which glucose is broken down to yield two molecules of a substance called pyruvate. Glycolysis has two distinct phases: an uphill preparatory phase and a downhill payoff phase. *Glycolysis involves a total of 10 steps. 1st ATP used is like a match to light a fire initiation energy / activation energy.
Destabilizes glucose enough to split it in two
*Two ATP molecules are used in the first five steos, one in step 1 and one in step 3. These reactions prime the glucose molecule by adding phsphate groups to its structure, which prepares the molecule for cleavage in steps 4 and 5 and a return on the energy investments in the last 5 steps. So its a little like again investing your money in the bank to gather interest on it.*In step 6 two NADH are produced, one from each of the two G3P molecules processed. In step 7 two ATP are produced through substrate level phosphorylation. In step 7 two ATP are produced by substrate level phosphorylation. One ATP for each of the 1,3-biphosphoglycerate (BPG) molecules processed.In step 10, two more ATP are formed by substrate level phophorylation as two molecules of phosphoenoyruvate are converted into two pyruvate molecules.All metabolic pathways are regulated. This means that the flow of metabolites can either be increased or decreased in response to the metabolic needs of the organism.*The steps that are the best candidates for regulation are those that have large negative free energy changes. Such reactions are essentially irreversible. They are the major control points of glycolysis*In glycolysis reactions 1, 3 and 10 all have large free energy changes. So these are the reguatory reactions. *The first regulated reaction of glycolysis step 1 is catalyzed by the enzyme hexokinase. If this reaction is blocked in a cell all of glycolysis stops and the cell will die. Cancer researchers are trying to find a way to turn hexokinase off to kill cancer cells.**Glucose is a stable molecule it needs an activation energy to break it apart.phosphorylate it = Pi comes from ATP.make NADH & put it in the bank for later.*And thats how life subsisted for a billion years.Until a certain bacteria learned how to metabolize O2; which was previously a poison.But now pyruvate is not the end of the processPyruvate still has a lot of energy in it that has not been captured.It still has 3 carbons bonded together! There is still energy stored in those bonds. It can still be oxidized further. **Cant stop at pyruvate == not enough energy producedPyruvate still has a lot of energy in it that has not been captured.It still has 3 carbons! There is still energy stored in those bonds.
*To form the acceptable 2 carbon acetyle CoA. The electrons in hydrogen are picked up by NAD+. What happens to this NAD+. It becomes reduced to form NADH. The 2-C acetyle CoA goes on to Krebs Cycle.**However the Krebs cycle utilizes a 2 Carbon moleculeCO2 is fully oxidized carbon == cant get any more energy out itCH4 is a fully reduced carbon == good fuel!!!
Why did we not keep the CO2? It was completely oxidized , lost all the hydrogens and we cant get anymore energy out of it.*We now enter the Krebs cycle. Now acetyl CoA joins with an oxaloacetate to create a 6 carbon molecule.*A 2 carbon sugar went into the Krebs cycle and was taken apart completely. Two CO2 molecules were produced from that 2 carbon sugar. Glucose has now been fully oxidized!
But wheres all the ATP??? *Everytime the carbons are oxidized, an NAD+ is being reduced.
But waitwheres all the ATP??*Citrate loses water to form aconitate. Aconitate picks up water and is rearranged to create isocitrate.Isocitrate encounters an NAD+ and reduces it to NADH. It then loses another CO2. Ketogluterate hooks up with Coenzyme A and releases 2electron, a hydrogen and a carbondioxide to form Succinyl CoA. Succinyl CoA reacts with an ADP and a phosphate releasing coenzyme A, ATP and forming succinate.Succinate encounters FAD and produces the energy carrier FADH2 and fumerate. Fumerate reacts with water to make malate. In the final reaction Malate encounters an NAD+ and produces the last of the NADH carriers and regenerates oxaloacetate***