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Transcript
CELLULAR RESPIRATION • • • • • • • • CONCEPT GLYCOLYSIS LINK REACTION KREB’S CYCLE ELECTRON TRANSPORT CHAIN CHEMIOSMOSIS ALTERNATIVE PATHWAYS ANAEROBIC REACTION AEROBIC REACTION GLYCOLYSIS • Location – cytosol • Biochemical pathway 1 Glucose (6C) 2 Pyruvates (3C) • Names and structures of enzymes involved not required except hexokinase and phosphofructokinase) • Net production of 2 ATP and 2 NADH • Glyco= sweet, sugar; • Catalysed by specific enzymes dissolves in cytosol • Occurs whether or not O2 is present • 2 phase: lysis = split – Energy Investment Phase (2 ATP used) – Energy Yielding Phase (4 ATP and 2 NADH are produced) How many net ATP produced? Phosphorylation • ATP is used to phosphorylate other substrate ATP Substrate ADP Substrate P • Phosphorylation – adding of phosphate group into a molecule making them chemically active GLYCOLYSIS ENERGY INVESTMENT PHASE STEP 4~splitting STEP STEP 1~ 2~ phosphorylation isomerization STEP 3~ phosphorylation STEP 5~isomerization •Fructose-1,6•C6 of glucose ~is an is •Isomerization •C1 of fructose-6-phosphate diphosphate is splitcatalyses phosphorylated •Isomerase isomerasethe catalyses the phosphorylated into tworeversible isomeris 3C •catalysed by hexokinase conversion rearrangement of glucose-6•requires anotherproducing ATP sugar produces: an two G3P’s phosphate to ATP its isomer, •produce•requires fructose-1,6-diphosphate dihydroxyacetoneph •makes glucose chemically fructose-6-phosphate osphate (DHAP) & reactive glyceraldehydes-3- •produces glucose-6phosphate (G3P) phosphate GLYCOLYSIS ENERGY PAYOFF PHASE/ ENERGY YEILDING PHASE Step 6: 7 STEP STEP 10 8 STEP & phosphorylation Phoshate Substrate-level group oxidation Substrate-level phosphorylation translocation •Glyceraldehyde-3-phosphate phosphorylation (G3P) is oxidized & NAD+ is •A phosphate •ATP is produced group byreduced •ATP is produced by + to NADH + H on C3 is transferred substrate level substrate-level •For each glucose molecule, 2 Step 9: to C2 phosphorylation phosphorylation NADH are produced Removal of water •Produce •A phosphate group •For each glucose •Glyceraldehyde-3-phosphate molecule is then 2 phosphorylated 2-phosphoglycerate is transferred from (G3P) molecule, ATP are onproduced C1 •Creates a double bond PEP to ADP •The phospate source is between C1 & C2 of the •For each glucose •Produce inorganic phosphate (not ATP!), substrate molecule, 2 ATP are which 3-phosphoglycerate present in the cytosol •Produce produced •Produce phosphoenolpyruvate •Produce pyruvate 1,3-diphosphoglycerate (PEP) (3C) Oxidative Decarboxylation LINK REACTION (FORMATION OF ACETYL COA) 1. Decarboxylation – Pyruvate (3C) is converted into 2C molecule by removing one CO2 2. Reduction – pyruvate is reduced producing 2 H+, NAD+ accept H+ and becomes NADH + H+ 3. The 2C compound called acetyl attaches to coenzyme A and form acetyl CoA KREB CYCLE REDOX • Oxidation and reduction at the same time • AH + B A + BH • A is oxidized • B is reduced STEP STEP4:5:OXIDATIVE SUBSTRATE DECARBOXYLATION LEVEL PHOSPHORYLATION • -Ketoglutarate removes CO2 = • Succinyl decarboxylation CoA is converted to 4C 7: HYDRATION STEP Succinate NAD+ is reduced to NADH + H+ = Water is added to Fumarate which • ATP dehydrogenation/oxidation produces = Substrate level STEP 3: OXIDATIVE DECARBOXYLATION rearranges the chemical bondsSTEP to form 6: 4C phosphorylation Malate DEHYDROGENATION/OXIDATION • Attachment of CoA to form 4C Succinyl 2 major events: • Breakdown CoA (high energy of Succinyl bond). CoA is STEP 8: • Succinate is oxidized to 4C coupled to the phosphorylation of DEHYDROGENATION/OXIDATION • Isocitrate loses CO2 leaving a 5C Fumarate and FAD is reduced. GDP to GTP. STEP 2: ISOMERIZATION compound = decarboxylation. STEP 1: ENTRY OF ACETYL GROUP Malate is oxidized and NAD+ is •to 2H are transferred to FAD to form • GTP then transfers its phosphate • Citrate is rearranged by two reactions. reduced to NADH + H+ • 5C compound is oxidized and NAD+ is FADH2 • Unstable bond attaching the Acetyl group to CoA breaks. ADP to+ form reduced to NADH H+ toATP. produce 5C •The first reaction, is removed. 4C water Oxaloacetate is regenerated. ketoglutarate = dehydrogenation/oxidation. • 2C Acetyl CoA becomes attached to a 4C Oxaloacetate, •Then water is added. • Forming 6C Citrate. •Through these two reactions Citrate is • CoA is free to combine another 2C Acetyl group. converted to itswith isomer, 6C Isocitrate • The process is repeated. STEP 1 •The unstable bond attaching the acetyl group to CoA breaks. •The 2C Acetyl CoA becomes attached to a 4C oxaloacetate molecule, •Forming citrate, a 6C molecule with 3 carboxyl groups. •CoA is free to combine with another 2C group. •The process is repeated STEP 2 •The citrate is rearranged by two preparation reactions. •The first reaction, water is removed. •Then water is added. •Through these two reactions citrate is converted to its isomer, isocitrate STEP 3 •Isocitrate loses CO2 leaving a 5C compound (decarboxylation). •The 5C compound is oxidized and NAD+ is reduced to NADH + H+ to produce ketoglutarate (dehydrogenation) STEP 4 •-Ketoglutarate undergoes decarboxylation (removal of CO2) •and dehydrogenation (NAD+ is reduced to NADH + H+) •Attachment of CoA to form 4C compound, succinyl CoA (high energy bond). STEP 5 •Succinyl CoA is converted to succinate •Substrate level phosphorylation takes place (ATP produced). •The breakdown of succinyl CoA is coupled to the phosphorylation of GDP to GTP. •GTP then transfers its phosphate to ADP to form ATP STEP 6 •Succinate is oxidized to fumarate and FAD is reduced. •2H are transferred to FAD to form FADH2 STEP 7 •Water is added to fumarate which rearranges the chemical bonds to form malate STEP 8 •Malate is oxidized and NAD+ is reduced to NADH + H+ •Oxaloacetate is regenerated SUBSTRATE LEVEL PHOSPHORYLATION Only few ATPs are directly produced by this Phosphorylation. 2 net ATP per glucose from Glycolisis 2 ATP per glucose in Krebs cycle 1. At the end of Krebs cycle, most energy extracted from glucose is in molecules of 6 NADH + H+ and 2 FADH2 2. These reduced compounds link glycolisis and Krebs Cycle to ETC by passing those electrons down to ETC to O2. 3. The transfer of electrons to O2 is exergonic leads to the formation of ATP • NAD+ + H+ + 2e- NADH (NAD is reduced, substrate is oxidized) • NADH NAD+ + H+ + 2e(NAD is oxidized, substrate is reduced) FOR 1 GLUCOSE.... GLYCOLYSIS • 2 net ATP produced • 2 NADH enter mitochondria as NADH/FADH (depend on the type of shuttles) • Malate-aspetate shuttle: NADH • Glycerol-phosphate shuttle: FADH2 Malate-aspertate shuttle Glycerol-phosphate shuttle FOR 1 GLUCOSE.... GLYCOLYSIS • 2 net ATP produced • 2 NADH enter mitochondria as NADH/FADH KREB CYCLE • 6 NADH (3X2 , 2 pyruvate) • 2 FADH (1X2, 2 pyruvate) • 2 ATP (1X2, 2 pyruvate) In Electron Transport Chain, • 1 molecule of NADH will generate 3 ATP • And 1 molecule of FADH2 will generate 2 ATP. PROCESS GLYCOLYSIS LINK REACTION KREB CYCLE TOTAL PRODUCT ATP 2 ATP 2 ATP 2 NADH /FADH 6 ATP 2 NADH 6 ATP 6 NADH 18 ATP 2 FADH 4 ATP 2 ATP 2 ATP 38 ATP / 4 ATP / 36 ATP Intermembrane space ATP Synthase FADH2 Complex I CoQ Complex II Complex III Cyt C Complex IV FAD : NADH Dehydrogenase : Coenzyme Q : Succinate Dehydrogenase : Cytochrome bc1 : Cytochrome C : Cytochrome c Oxidase Intermembrane space ATP Synthase FADH2 FAD 1. NADH + H+ oxidizes, transfer H+ and 2e to complex I Intermembrane space ATP Synthase FADH2 FAD 2. The transfer of electron cause complex I to pump H+ to intermembrane space Intermembrane space ATP Synthase FADH2 FAD 3. Complex I then transfer e to CoQ, a lipid soluble mobile electron carrier Intermembrane space ATP Synthase FADH2 FAD 4. CoQ transfer e to complex III Intermembrane space ATP Synthase FADH2 FAD 5. This transfer of e cause complex III to pump H+ to intermembrane space Intermembrane space ATP Synthase FADH2 FAD 6. Complex III then transfer e to cyt c, another mobile e carrier Intermembrane space ATP Synthase FADH2 FAD 7. Cyt c transfer e to complex IV, again H+ is pumped to intermembrane space Intermembrane space ATP Synthase FADH2 FAD 8. Complex IV lastly transfer e to O2 (last e acceptor) Intermembrane space ATP Synthase FADH2 FAD 9. O2 acccept 4e with 4H+ and becomes 2 water molecules O2 + 4e- + 4H+ 2H2O Intermembrane space ATP Synthase FADH2 FAD REMEMBER: complex I, III and IV has been pumping H+ to the intermembrane space! This create a H+ gradient: H+ concentration in intermembrane space higher than in matrix. Intermembrane space ATP Synthase FADH2 FAD This concentration gradient switch on the ATP synthase for CHEMIOSMOSIS. H+ will be pumped back to matrix. This pumping generate ATP ATP synthase add inorganic phosphate (Pi) to ADP ATP Intermembrane space ATP Synthase FADH2 FAD How about complex II? Complex II undergo the same process but only accepts H+ from FADH2, Complex II is a peripheral proteins, it cant pump H+ Intermembrane space ATP Synthase FADH2 FAD Complex II except e from FADH2, pass it to CoQ and then to complex III FADH2 will not encounter complex I, thus, for FADH2, H+ will be pumped twice. Cellular respiration ANAEROBIC AND ALTERNATIVE PATHWAY ANAEROBIC RESPIRATION & OTHER MACROMOLECULES METABOLIC PATHWAYS OBJECTIVES: 1. DEFINITION OF ANAEROBIC RESPIRATION. 2. DIFFERENCES BETWEEN AEROBIC AND ANAEROBIC RESPIRATION. 3. PRODUCTS OF GLYCOLISIS. 4. FERMENTATION – LACTIC ACID & ETHANOL FORMATION. 5. IMPORTANCE OF FERMENTATION IN INDUSTRY 6. OTHER MACROMOLECULES METABOLIC PATHWAYS. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Overview of Glucose Catabolism 1. Anaerobic Respiration – In the absence of oxygen, some organisms can still respire anaerobically, using inorganic molecules to accept electrons. • Methanogens • Sulfur Bacteria Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Fig. 9.9 Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies RELATED METABOLIC PROCESSES 1. FERMENTATION ● enables some cells to produce ATP without the presence of O2. ● anaerobic catabolism of organic nutrients. ► Oxidizing agent : NAD+ , not O2. ► Involves glycolisis followed by pyruvate reduction by NADH. ► Result: 2 ATPs. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Anaerobic Routes of ATP Formation • Fermentation pathways – Bacteria, yeasts and protistans – Intensive Exercising • Glycolysis - first step • Net yield of two ATP • Final product is lactate or ethanol Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies LACTIC ACID FERMENTATION 1. Intensive exercising, O2 is scarce, human muscle cells switch from aerobic respiration to lactic acid fermentation. ● Lactate accumulates. ● Gradually it is carried to liver, to be converted back to pyruvate when O2 is available. (O2 Debt) 2. Commercial Importance: cheese production, yoghurt. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Lactate Fermentation • Muscle cells in animals • Quick ATP production • Some bacteria Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies ALCOHOL FERMENTATION 1. 2. 3. 4. 5. Pyruvate loses CO2. Pyruvate is converted to 2C Acetaldehyde. NADH is oxidized to NAD+. Acetaldehyde is reduced to ethanol. Examples: Yeast, Bacteria Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Alcohol Fermentation • Acetaldehyde is intermediate product • Yeasts Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies FERMENTATION & RESPIRATION: COMPARISON 1. Similarity: ● Both use glycolisis to oxidize glucose and other substrates to pyruvate. ● Produce 2 ATPs by substrate-levelphosphorylation. ● Use NAD+ as oxidizing agent in glycolisis. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies 2. Differences: ● Fermentation produce NAD+ during the reduction of pyruvate to form lactate or ethanol and CO2. ● Aerobic respiration produce NADH during the oxidation of intermediates. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies 3. Final electron acceptor: ● Fermentation: pyruvate acts as the final electron acceptor. ● Cell respiration: O2 is the final electron acceptor. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies 4. Amount of energy harvested: ● Fermentation yields net 2 ATPs by substrate- level phosphorylation. ● Cell respiration: 18 times more by substrate-level phosphorylation and oxidative phosphorylation. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies 5. Requirement of O2: ● Fermentation does not require O2. ● Cell respiration occurs only in the presence of O2. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies 6. Occurrence: ● Fermentation happens in cytosol. ● Cell Respiration occurs in cytosol and mitochondria. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies OTHER METABOLIC PATHWAYS 1. Glycolisis and Krebs Cycle can connect to many other metabolic pathways. 2. Cell respiration can oxidize organic molecules other than glucose to make ATP. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Fig. 9.21 Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies 1. PROTEINS - hydrolyzed to amino acids. 2. Excess Amino Acids - enzymatically converted to intermediates of glycolisis & Krebs Cycle. (Pyruvate, Acetyl CoA, -ketoglutarate). 3. This conversion deaminates amino acids, nitrogenous waste are excreted & carbon skeleton can be oxidized. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies 1. FATS - rich in hydrogens. (high energy electrons) 2. Oxidation of 1 g of fat produces 2 times more ATP than 1 g of Carbohydrate. 3. Fats- digested into glycerol and fatty acids. 4. Glycerol can be converted into glyceraldehydes phosphate (intermediate of glycolisis). 5. Fatty acids – converted into Acetyl CoA by βoxidation. The 2C compounds enter Krebs Cycle. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Review • Chemical Energy Drives Metabolism • Glucose Catabolism – Glycolysis – Pyruvate Oxidation – Krebs Cycle – Electron Transport Chain • Aerobic Respiration Summary • Energy Storage • Fermentation Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display Raven - Johnson - Biology: 6th Ed. - All Rights Reserved McGraw Hill Companies Fig.Raven 9.9a- Johnson - Biology: 6th Ed. - All Rights Reserved Copyright © Companies 2002 Pearson Education, Inc., publishing as Benjamin Cummings McGraw Hill Fig. 9.9b - Biology: 6th Raven - Johnson Ed. - All Rights Reserved Copyright © Companies 2002 Pearson Education, Inc., publishing as Benjamin Cummings McGraw Hill Raven - Johnson - Biology: 6thFig. 9.11 Ed. - All Rights Reserved Copyright © Companies 2002 Pearson Education, Inc., publishing as Benjamin Cummings McGraw Hill • The conversion of pyruvate and the Krebs cycle produces large quantities of electron carriers. Raven - Johnson - Biology: 6th Fig. 9.12 Ed. - All Rights Reserved Copyright © Companies 2002 Pearson Education, Inc., publishing as Benjamin Cummings McGraw Hill Fig. 9.15 Raven - Johnson - Biology: 6th Ed. - All Rights Reserved Copyright © Companies 2002 Pearson Education, Inc., publishing as Benjamin Cummings McGraw Hill