Cellular respiration AP Biology Cellular Respiration Stage 1

Cellular respiration AP Biology

Cellular Respiration Stage 1: Glycolysis AP Biology 2007 -2008

What’s the point? The point is to make ATP! ATP AP Biology 2007 -2008

Glycolysis § Breaking down glucose u “glyco – lysis” (splitting sugar) glucose pyruvate 2 x 3 C 6 C u ancient pathway which harvests energy § where energy transfer first evolved § transfer energy from organic molecules to ATP § still is starting point for ALL cellular respiration u but it’s inefficient § generate only 2 ATP for every 1 glucose u occurs in cytosol AP Biology That’s not enough ATP for me! In the cytosol? Why does that make evolutionary sense?

Evolutionary perspective § Prokaryotes u first cells had no organelles Enzymes of glycolysis are “well-conserved” § Anaerobic atmosphere u u life on Earth first evolved without free oxygen (O 2) in atmosphere energy had to be captured from organic molecules in absence of O 2 § Prokaryotes that evolved glycolysis are ancestors of all modern life u AP Biology ALL cells still utilize glycolysis You mean we’re related? Do I have to invite them over for the holidays?

Overview glucose C-C-C-C 10 reactions enzyme 2 ATP 2 ADP convert fructose-1, 6 b. P glucose (6 C) to P-C-C-C-P enzyme 2 pyruvate (3 C) enzyme u produces: DHAP G 3 P 4 ATP & 2 NADH P-C-C-C-P 2 H u consumes: 2 Pi enzyme 2 ATP enzyme u net yield: 2 Pi enzyme 2 ATP & 2 NADH u DHAP = dihydroxyacetone phosphate AP Biology G 3 P = glyceraldehyde-3 -phosphate pyruvate C-C-C 2 NAD+ 2 4 ADP 4 ATP

Glycolysis summary endergonic invest some ATP ENERGY INVESTMENT -2 ATP G 3 P ENERGY PAYOFF C-C-C-P 4 ATP exergonic harvest a little ATP & a little NADH like $$ in the bank NET YIELD AP Biology net yield ü 2 ATP ü 2 NADH

1 st half of glycolysis (5 reactions) Glucose “priming” u get glucose ready to split § phosphorylate glucose § molecular rearrangement u ADP Glucose 6 -phosphate 2 Fructose 6 -phosphate 3 ATP phosphofructokinase O CH 2 ADP CH 2 O O P CH 2 4, 5 aldolase isomerase O Dihydroxyacetone CH 2 OH phosphate AP Biology P O CH 2 OH Fructose 1, 6 -bisphosphate C NAD+ O CH 2 O O phosphoglucose isomerase split destabilized glucose P CH 2 OH Glucose 1 ATP hexokinase H Glyceraldehyde 3 -phosphate (G 3 P) Pi NAD 6 glyceraldehyde NADH 3 -phosphate P dehydrogenase 1, 3 -Bisphosphoglycerate (BPG) Pi + C O CHOH CH 2 O O P O CHOH CH 2 O P

2 nd half of glycolysis (5 reactions) DHAP P-C-C-C Energy Harvest u NADH production § § u G 3 P donates H oxidizes the sugar reduces NAD+ NADH Pi NAD+ phosphorylation” § ADP ATP AP Biology Pi 6 NAD+ NADH 7 phosphoglycerate kinase ADP ATP 3 -Phosphoglycerate (3 PG) 8 phosphoglyceromutase 2 -Phosphoglycerate (2 PG) Phosphoenolpyruvate (PEP) H 2 O Phosphoenolpyruvate (PEP) 10 pyruvate kinase ADP ATP Pyruvate OC CHOH CH 2 O P O- 2 -Phosphoglycerate (2 PG) 9 enolase H 2 O ADP Payola! Finally some ATP! C-C-C-P NADH ATP production § G 3 P pyruvate § PEP sugar donates P w “substrate level G 3 P Pyruvate C O H C O CH 2 OH P OC C CH 2 O O OC O CH 3 P

Substrate-level Phosphorylation § In the last steps of glycolysis, where did the P come from to make ATP? u 9 the sugar substrate (PEP) HO enolase H 2 O 2 P is transferred from PEP to ADP ükinase enzyme üADP ATP AP Biology Phosphoenolpyruvate (PEP) ADP Phosphoenolpyruvate (PEP) 10 pyruvate kinase ATP Pyruvate ATP I get it! The Pi came directly from the substrate! ADP Pyruvate OC O CH 2 OC O CH 3 P

Energy accounting of glycolysis 2 ATP 2 ADP glucose pyruvate 2 x 3 C 6 C 4 ADP 4 ATP 2 NAD+ 2 § Net gain = 2 ATP + 2 NADH u u All that work! And that’s all I get? But glucose has so much more to give! some energy investment (-2 ATP) small energy return (4 ATP + 2 NADH) §AP Biology 1 6 C sugar 2 3 C sugars

Is that all there is? § Not a lot of energy… u for 1 billon years+ this is how life on Earth survived § no O 2 = slow growth, slow reproduction § only harvest 3. 5% of energy stored in glucose w more carbons to strip off = more energy to harvest O 2 O 2 AP Biology O 2 glucose pyruvate 2 x 3 C 6 C Hard way to make a living!

But can’t stop there! G 3 P DHAP NAD+ raw materials products Pi + NADH Pi 1, 3 -BPG NAD+ Pi + NADH NAD 1, 3 -BPG NADH 7 ADP Glycolysis 6 Pi ADP ATP 3 -Phosphoglycerate (3 PG) 2 -Phosphoglycerate (2 PG) glucose + 2 ADP + 2 Pi + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH 8 § Going to run out of NAD+ u u H 2 O 9 without regenerating NAD+, energy production would stop! Phosphoenolpyruvate (PEP) another molecule must accept H ADP 10 from NADH ATP § so NAD AP Biology + is freed up for another round Pyruvate H 2 O Phosphoenolpyruvate (PEP) ADP ATP Pyruvate

How is NADH recycled to NAD+? without oxygen with oxygen Another molecule aerobic respiration must accept H pyruvate from NADH H 2 O O 2 recycle NADH anaerobic respiration “fermentation” NAD+ NADH acetyl-Co. A CO 2 NADH NAD+ lactate acetaldehyde NADH NAD+ lactic acid fermentation which path you use depends on AP Biology who you are… Krebs cycle ethanol alcohol fermentation

REVIEW 10 reactions glucose C-C-C-C 2 ATP 2 ADP convert fructose-1, 6 b. P glucose (6 C) to P-C-C-C-P 2 pyruvate (3 C) u produces: DHAP G 3 P 4 ATP & 2 NADH P-C-C-C-P 2 H u consumes: 2 Pi 2 ATP u net: 2 Pi 2 ATP & 2 NADH u AP Biology pyruvate C-C-C 2 NAD+ 2 4 ADP 4 ATP

Cellular Respiration Stage 2 & 3: Oxidation of Pyruvate and the Krebs Cycle AP Biology 2006 -2007

Glycolysis is only the start § Glycolysis glucose pyruvate 6 C 2 x 3 C § Pyruvate has more energy to yield u u u 3 more C to strip off (to oxidize) if O 2 is available, pyruvate enters mitochondria enzymes of Krebs cycle complete the full oxidation of sugar to CO 2 pyruvate CO 2 AP Biology 3 C 1 C

Mitochondria — Structure § Double membrane energy harvesting organelle u u smooth outer membrane highly folded inner membrane § cristae u intermembrane space § fluid-filled space between membranes u matrix § inner fluid-filled space u u DNA, ribosomes enzymes § outer intermembrane inner free in matrix & membrane-bound space membrane cristae matrix What cells would have AP Biology a lot of mitochondria? mitochondrial DNA

Mitochondria – Function Oooooh! Form fits function! Dividing mitochondria Membrane-bound proteins Who else divides like that? Enzymes & permeases bacteria! What does this tell us about the evolution of eukaryotes? Endosymbiosis! AP Biology Advantage of highly folded inner membrane? More surface area for membranebound enzymes & permeases

Oxidation of pyruvate § Pyruvate enters mitochondrial matrix [ 2 x pyruvate acetyl Co. A + CO 2 3 C 2 C 1 C NAD Where does the CO 2 go? Exhale! 3 step oxidation process u releases 2 CO 2 (count the carbons!) u reduces 2 NADH (moves e-) u produces 2 acetyl Co. A u § Acetyl Co. A enters Krebs cycle AP Biology ]

Pyruvate oxidized to Acetyl Co. A reduction NAD+ Pyruvate C-C-C [ CO 2 Coenzyme A oxidation Acetyl Co. A C-C 2 x Yield = 2 C sugar + NADH + CO 2 AP Biology ]

Krebs cycle 1937 | 1953 § aka Citric Acid Cycle in mitochondrial matrix u 8 step pathway u Hans Krebs § each catalyzed by specific enzyme 1900 -1981 § step-wise catabolism of 6 C citrate molecule § Evolved later than glycolysis u AP Biology does that make evolutionary sense? § bacteria 3. 5 billion years ago (glycolysis) § free O 2 2. 7 billion years ago (photosynthesis) § eukaryotes 1. 5 billion years ago (aerobic respiration = organelles mitochondria)

Count the carbons! pyruvate 3 C 2 C 6 C 4 C This happens twice for each glucose molecule AP Biology 4 C acetyl Co. A citrate oxidation of sugars CO 2 x 2 4 C 4 C 6 C 5 C 4 C CO 2

Count the electron carriers! pyruvate 3 C FADH 2 AP Biology 6 C 4 C NADH This happens twice for each glucose molecule 2 C 4 C acetyl Co. A citrate reduction of electron carriers x 2 4 C 4 C ATP CO 2 NADH 6 C CO 2 NADH 5 C 4 C CO 2 NADH

So we fully oxidized glucose C 6 H 12 O 6 CO 2 & ended up with 4 ATP! AP Biology What’s the point?

Electron Carriers = Hydrogen Carriers H+ § Krebs cycle produces large quantities of electron carriers NADH u FADH 2 u go to Electron Transport Chain! u AP Biology What’s so important about electron carriers? H+ H+ H+ H+ ADP + Pi ATP H+

Energy accounting of Krebs cycle 4 NAD + 1 FAD 4 NADH + 1 FADH 2 2 x pyruvate CO 2 3 x 1 C 3 C 1 ADP 1 ATP Net gain = 2 ATP = 8 NADH + 2 FADH 2 AP Biology

Value of Krebs cycle? § If the yield is only 2 ATP then how was the Krebs cycle an adaptation? u value of NADH & FADH 2 § electron carriers & H carriers w reduced molecules move electrons w reduced molecules move H+ ions § to be used in the Electron Transport Chain like $$ in the bank AP Biology

What’s the point? The point is to make ATP! ATP AP Biology 2006 -2007

Cellular Respiration Stage 4: Electron Transport Chain AP Biology 2006 -2007

ATP accounting so far… § Glycolysis 2 ATP § Kreb’s cycle 2 ATP § Life takes a lot of energy to run, need to extract more energy than 4 ATP! There’s got to be a better way! I need a lot more ATP! AP Biology A working muscle recycles over 10 million ATPs per second

There is a better way! § Electron Transport Chain u series of proteins built into inner mitochondrial membrane § along cristae § transport proteins & enzymes transport of electrons down ETC linked to pumping of H+ to create H+ gradient u yields ~36 ATP from 1 glucose! u only in presence of O 2 (aerobic respiration) u AP Biology That sounds more like it! O 2

Mitochondria § Double membrane outer membrane u inner membrane u § highly folded cristae § enzymes & transport proteins u intermembrane space § fluid-filled space between membranes AP Biology Oooooh! Form fits function!

Electron Transport Chain Inner mitochondrial membrane Intermembrane space C Q NADH dehydrogenase cytochrome bc complex Mitochondrial matrix AP Biology cytochrome c oxidase complex

Remember the Electron Carriers? Glycolysis 2 NADH Time to break open the piggybank! AP Biology glucose Krebs cycle G 3 P 8 NADH 2 FADH 2

Electron Transport Chain Building proton gradient! NADH NAD+ + H e p intermembrane space H+ H+ H e- + H+ C e– NADH H FADH 2 NAD+ NADH dehydrogenase inner mitochondrial membrane e– Q AP Biology H+ e– H FAD 2 H+ + 12 O 2 cytochrome bc complex H 2 O cytochrome c oxidase complex mitochondrial matrix What powers the proton (H+) pumps? …

Stripping H from Electron Carriers § Electron carriers pass electrons & H+ to ETC u u H cleaved off NADH & FADH 2 electrons stripped from H atoms H+ (protons) § electrons passed from one electron carrier to next in mitochondrial membrane (ETC) § flowing electrons = energy to do work u transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space TA-DA!! Moving electrons do the work! + H H+ H+ H+ H H+ C e– NADH AP Biology + H H+ H+ Q e– FADH 2 FAD NAD+ NADH dehydrogenase e– 1 2 H+ + cytochrome bc complex 2 O 2 H 2 O cytochrome c oxidase complex ADP + Pi ATP H+

But what “pulls” the electrons down the ETC? H 2 O O 2 AP Biology electrons flow downhill to O 2 oxidative phosphorylation

Electrons flow downhill § Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative u controlled oxidation u controlled release of energy u make ATP instead of fire! AP Biology

“proton-motive” force We did it! § Set up a H+ § § H+ H+ gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + Pi ATP Are we there yet? AP Biology H+ H+ H+ ADP + Pi ATP H+

Chemiosmosis § The diffusion of ions across a membrane u build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis links the Electron Transport Chain to ATP synthesis So that’s the point! AP Biology

1961 | 1978 Peter Mitchell § Proposed chemiosmotic hypothesis u revolutionary idea at the time proton motive force 1920 -1992 AP Biology

Pyruvate from cytoplasm Inner + mitochondrial H membrane H+ Intermembrane space Electron transport C system Q NADH Acetyl-Co. A 1. Electrons are harvested and carried to the transport system. NADH Krebs cycle e- e- FADH 2 e- 2. Electrons provide energy to pump protons across the membrane. 3. Oxygen joins with protons to form water. e- H 2 O 1 O 2 +2 2 H+ O 2 H+ CO 2 ATP Mitochondrial matrix AP Biology H+ ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. H+ ATP synthase

~4 0 A Cellular respiration 2 ATP AP Biology + 2 ATP + ~36 ATP TP

Summary of cellular respiration C 6 H 12 O 6 + 6 O 2 § § § § 6 CO 2 + 6 H 2 O + ~40 ATP Where did the glucose come from? Where did the O 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the ATP come from? What else is produced that is not listed in this equation? § Why do we breathe? AP Biology

Taking it beyond… § What is the final electron acceptor in Electron Transport Chain? O 2 § So what happens if O 2 unavailable? § ETC backs up nothing to pull electrons down chain u NADH & FADH 2 can’t unload H u AP Biology § ATP production ceases § cells run out of energy § and you die!

What’s the point? The point is to make ATP! ATP AP Biology 2006 -2007