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Cellular Respiration: Krebs cycle and ETC

Cellular Respiration: Krebs cycle and ETC. IB HL Biology 1. Cell Respiration - controlled release of energy from organic compounds in cells to form ATP. Aerobic Cellular Respiration a metabolic pathway with over 20 reactions, using 20 enzymes. Why cell respiration?.

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Cellular Respiration: Krebs cycle and ETC

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  1. Cellular Respiration:Krebs cycle and ETC IB HL Biology 1

  2. Cell Respiration- controlled release of energy from organic compounds in cells to form ATP Aerobic Cellular Respirationa metabolic pathway with over 20 reactions, using 20 enzymes

  3. Why cell respiration? • Cells require a constant source of energy to perform various tasks • Movement • Transport • Division

  4. Summary Equation • The summary equation for cellular respiration is: C6H12O6 + O2 CO2 + H2O + Glucose + oxygen  carbon dioxide + water + ATP ATP

  5. Key players in this process • Glucose: source of fuel • NAD+: electron carrier • Enzymes: mediate entire process • Mitochondria: site of aerobic respiration • ATP: principal end product • Protons/Electrons: sources of potential energy • Oxygen: final electron acceptor

  6. Redox Reactions • Reduction: reducing overall positive charge by gaining electrons • Oxidation: loss of electrons • OIL RIG • Oxidation Is Loss of e- and addition of oxygen • Reduction Is Gain of e- and loss of oxygen • Redox reactions produce energy change • Reduction absorbs energy (endergonic) • Oxidation releases energy (exergonic)

  7. Respiration is a controlled release of energy • It’s a highly exergonic, but well-controlled process • Mediated by enzymes, electron carriers • Otherwise, it would be like an explosion • Not compatible with life!

  8. Phosphorylation • Addition of a phosphate group to a molecule; ex. Adding PO4 to ADP to form ATP • Occurs in two ways • Substrate level phosphorylation • Oxidative phosphorylation

  9. Substrate-level phosphorylation • An enzyme transfers a phosphate group from a substrate to ADP • Making ATP with an enzyme • Ineffective in generating large amounts of ATP • Occurs during glycolysis; addition of PO4 to glucose and ATP is made when pyruvate loses PO4 to ADP

  10. Oxidative phosphorylation • Refers to phosphorylation that occurs due to redox reactions transferring electrons from food to oxygen • Occurs in electron transport chains in mitochondrion • Makes ATP using energy derived redox reactions

  11. Three stages of cell respiration • Stage 1: Glycolysis (energy investment) • Some ATP is made, some is used • Stage 2: Krebs Cycle (oxidation of pyruvate) • Generation of CO2 • Stage 3: Oxidative Phosphorylation -ETC • Generation of most ATP

  12. Three stages of respiration

  13. General Outline • Glucose Glycolysis No Oxygen Anaerobic Oxygen Aerobic Pyruvic Acid Transition Reaction Fermentation Krebs Cycle ETS 2 ATP 36-38 ATP

  14. Mitochondrion--Structure and Function2 phospholipids bilayers with embedded protein • Inner Membrane • Contains folds called cristae • Cristae contain carriers of ETC • Inter-membrane Space • Space between outer and inner membrane • ETC pumps H+ here for oxidative phosphorylation • Matrix • Space inside inner membrane • Contains enzymes, ribosomes, small loops of DNA and metabolites • acetylCoA formed here • Krebs cycle occurs here

  15. Mitochondrion The outer membrane is fairly smooth. But the inner membrane is highly convoluted, forming folds called cristae. The cristae greatly increase the inner membrane's surface area. • Mitochondria are membrane-bound organelles On these cristae organic molecules are combined with oxygen to produce ATP - the primary energy source for the cell.

  16. 8.1.3 Structure of the mitochondria. • Location of aerobic respiration • Pyruvate, the product of glycolysis can be further oxidized here to release more energy. • Mitochondria are only found in eukaryotic cells. • Cells that need a lot of energy will have many mitochondria ( liver cell) or can develop them under training (muscles cells). • There is a double membrane. • The inner membrane is folded to form 'cristae'. • There is a space between the two membranes which is important for creating a place to concentrate H+ (see 8.1.6 ) • The inner space is called the matrix. • Mitochondria contain some of their own DNA (mDNA). 8.1.6 Relationship between the structure and function of the mitochondria. 1. Cristae folds increase the surface area for electron transfer system. 2. The double membrane creates a small space into which the H+ can be concentrated. 3. Matrix creates an isolated space in which the Krebs cycle can occur.

  17. DRAW AND LABEL A DIAGRAM SHOWING THE STRUCTURE OF A MITOCHONDRION AS SEEN IN ELECTRON MICROGRAPHS.

  18. General Outline of Aerobic Respiration • Glycolysis Transition or Link Reaction Krebs Cycle Electron Transport System

  19. Aerobic Cellular Respiration electrons electrons Glycolysis Krebs Cycle ETC & chemiosmosis glucose pyruvate ATP ATP ATP

  20. Krebs Cycle • When O2 is present, pyruvate enters mitochondrion, enzymes of the Krebs cycle complete the oxidation of the organic fuel • Upon entering, pyruvate is converted to acetyl coenzyme A (acetyl CoA) • This step is the transition between glycolysis and Krebs cycle; is called the link reaction • It is accomplished by a multi-enzyme complex that catalyzes three reactions

  21. Transition to the Krebs cycle Link Reaction Step 1: carboxyl group removed, CO2 diffuses out Step 2: remaining 2-carbon fragment is oxidized, forms acetate • enzyme transfers extracted electrons to NAD+, storing energy in form of NADH Step 3: coenzyme A attaches to acetate by unstable bond, makes acetyl group very reactive The final product is acetyl Co-A, which enters Krebs cycle for further oxidizing

  22. Conversion of pyruvate to acetyl CoA

  23. Krebs cycle has eight steps, each catalyzed by a specific enzyme • For each turn, two carbons enter as acetate, and two different carbons leave in oxidized form of CO2 • Acetate joins the cycle by its enzymatic addition to oxaloacetate, forming citrate • Subsequent steps decompose oxaloacetate, giving off CO2 • It is the regeneration of oxaloacetate that accounts for the “cycle” in the Krebs cycle

  24. Most of energy harvested by oxidative steps is conserved in NADH. • for each acetate that enters the cycle, three NAD+ are reduced to NADH. • In one oxidative step, electrons are transferred to FAD (flavin adenine dinucleotide). • reduced form FADH2 donates its electrons to the electron transport chain • Another step forms an ATP by substrate-level phosphorylation • NADH and FADH2 relay extracted electrons to electron transport chain to make ATP by oxidative-phosphorylation • Krebs cycle turns twice, once for each of the two pyruvate generated by glycolysis

  25. Krebs Cycle Animation

  26. Summary of Krebs Cycle

  27. Transition or Link Reaction (refer to p273 Clegg) Links glycolysis with reactions occuring in mitochodria • Pyruvate diffuses into mitochondrial matrix • It is decarboxylated by removal of CO2 and oxidized by removal of H+ • NAD is reduced by addition of e- and H+ • A two-carbon acetyl group is formed and combines with Coenzyme A to make acetyl CoA, which enters the Krebs cycle Pyruvic Acid Acetyl CoA CO2

  28. Stage 2: Krebs cycle (refer to p273 Clegg) • Where: • Matrix of mitochondria, but only if O2 present • Why: • To oxidize pyruvate to CO2 • To build up a H+ ion gradient used in electron transport • FAD and NAD are reduced • FAD is chief H-carrying coenzyme in ETC

  29. Krebs cycle summary • Per acetyl CoA that enters: • 1 ATP made • 2 CO2 given off • 3 NADH produced • 1 FADH2 produced • Think: how many acetyl CoA entered the cycle? • How many times must this cycle happen to break down ONE glucose? • Refer to p274 Clegg text Table 9.1

  30. Aerobic Cellular Respiration electrons electrons ETC & chemiosmosis Glycolysis Krebs Cycle pyruvate glucose ATP ATP ATP

  31. Stage 3: Oxidative phosphorylation • Where: • Inner membrane of mitochondria (on cristae) • Why: • To produce ATP from H+ ion gradient generated during Krebs cycle • Requires oxygen! • ETC Movie

  32. Oxidative Phosphorylation and ETC (refer to p275 Clegg) • Chemiosmosis is process by which synthesis of ATP is coupled with ETC by H+ movement • Occurs in the cristae folds of inner mitochondrial membrane where e- carrier proteins are arranged • 4 protein-based complexes that work in sequence moving H+ • Carrier proteins oxidize the reduced coenzymes • Energy from this process pumps H+ from matrix to the inter-membrane space (proton pumps)

  33. Oxidative Phosphorylation and ETC (refer to p275 Clegg) • A concentration of H+ ions accumulate between the inner and outer membranes; the H+ contain energy like a dam and pH decreases • H+ concentration gradient creates a potential difference across the membrane • Thiscauses the synthesis of ATP by chemiosmosis as H+ flow back into membrane via channels in ATPase enzymes and APTase uses energy from gradient to make ATP • Energized e- & H+ from the 10 NADH2 and 2 FADH2(produced during glycolysis & Krebs cycle) are transferred to O2 to produce H2O(redox reaction)O2  +  4e-  +  4H+  2H2O

  34. Summary: Oxidative Phosphorylation • 34 ATP made • H2O generated • NADH oxidized back to NAD • Very efficient process! Produces a lot of energy.

  35. Electron Transport Chain: Found in the inner mitochondrial membrane or cristae Contains 4 protein-based complexes that work in sequence moving H+ from the matrix across the inner membrane (proton pumps) A concentration gradient of H+ between the inner & outer mitochondrial membrane occurs H+ concentration gradient causes the synthesis of ATP by chemiosmosis Energized e- & H+ from the 10 NADH2 and 2 FADH2 (produced during glycolysis & Krebs cycle) are transferred to O2 to produce H2O (redox reaction) O2 + 4e- + 4H+ 2H2O

  36. H+ H+ H+ H+ H+ H+ H+ Electron Transport Chain & Chemiosmosis intermembrane space  Chemiosmosis  ATP synthetase: proton pump inner mito. membrane The importance of e-?!? Force the displacement of H+ from the matrix to intermembrane space ADP + Pi ATP matrix

  37. Electron Transport Chain & Chemiosmosis NAD+ H+ NADH H+ H+ + H+

  38. Electron Transport Chain & Chemiosmosis H+ NAD+ H+ NADH H+ + H+

  39. Electron Transport Chain & Chemiosmosis H+ H+ NAD+ H+ NADH + H+

  40. Electron Transport Chain & Chemiosmosis H+ H+ H+ 2 H+ + ½ O2 H20 NAD+ NADH + H+ electon transport chain chemiosmosis

  41. ADP + P Electron Transport Chain & Chemiosmosis H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ 2 H+ + ½ O2 H20 NAD+ NADH ATP + H+

  42. C6H12O6 + 6O2 --> 6CO2 + 6H2O+ energy to make 38 ATP

  43. Other molecules can be used in respiration • Proteins: must be deaminated, then converted to pyruvate • Fats: undergo beta-oxidation • Cells prefer carbs

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