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8.2 cell respiration
- 2. Understandings Cell respiration involves the oxidation and reduction of electron carriers. Phosphorylation of molecules makes them less stable. In glycolysis, glucose is converted into pyruvate in the cytoplasm. Glycolysis gives a small net gain of ATP without the use of oxygen. In aerobic cell respiration, pyruvate is decaroxylated and oxidized, and converted to acetyl compound and attached to coenzyme A to form acetyl coenyme A in the link reaction. In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of H carriers, liberating carbon dioxide. Energy released by oxidation reactions is carried to the cristae of the mitochondrion by reduced FAD and NAD+. Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping. In chemiosmosis protons diffuse through ATP synthase to generate ATP. Oxygen is needed to bind with the free protons to form water to maintain the H gradient The structure of the mitochondrion is adapted to the function it performs.
- 3. Applications/Skills Guidance A: Electron tomography used to produce images of active mitochondria. S: Analysis of diagrams of the pathways of aerobic respiration to deduce where decaroxylation and oxidation reactions occur. S: Annotation of a diagram of mitochondrion to indicate the adaptations to its functions. The names of the intermediate compounds in glycolysis and the Krebs cycle are not required.
- 4. Oxidation: Results in a compound with lower potential energy Reduction: Results in a compound with higher potential energy Comparison of Oxidation and Reduction
- 5. Reduction and Oxidation Reaction: Electron carriers • Electron carriers are substances that accept and give up electrons as required. • They often link oxidations and reductions in cells. • Main electron carrier is NAD + (nicotinamide adenine dinucleotide), it is a coenzyme • It’s Reduced to NADH when it picks up two electrons and one hydrogen ion NAD+ + 2 H ⇒ NADH + H+ FAD + 2 H ⇒ FADH2
- 7. Structure mitochondrion like in micrographs
- 8. Glucose (6C) Glucose phosphate (6C) Fructose bisphosphate (6C) glicerate 3-phosphate (3C) glicerate 3-phosphate (3C) Pyruvate (3C) Pyruvate (3C) ATP ADP + Pi ATP ADP + Pi 2 ADP + Pi 2 ADP + Pi 2 ATP 2 ATP NAD+ NADH + H + NAD+ NADH + H + Glycolysis PHOSPORILATION LYSIS OXIDATION & ATP FORMATION
- 9. Aerobic respiration: the link reaction Acetyl Coenzyme A (2C) Coenzyme A Pyruvate (3C) Acetate (2C) + CO2 NAD+ NADH + H + Pyruvate (3C) enters the matrix of the mitochondria from the cytoplasm Pyruvate + CoA +NAD+ acetyl-CoA + CO2 +NADH + H+
- 10. Aerobic respiration: Krebs Cycle 1. Acetyl Co-A combines with a 4-carbon compound (oxalacetate) to form a six-carbon compound (citrate) 2. A series of reactions take place where the citrate (6C) is both decarboxylated and dehydrogenated 3. The most important role of the Krebs cycle is to provide hydrogen that can be used in the electron transport chain to provide energy for the formation
- 11. Aerobic respiration: The electron transport chain The final stage occurs in the inner membranes of mitochondria. This stage has two parts: an electron transport chain and ATP production by ATP synthase
- 12. Electron Transport Chain & Oxidative phosphorylation Chemiosmosis couples the electron transport chain to ATP synthesis
- 13. Relationship between structure of mitochondrion and its function 1. Cristae: Large Surface Area for the Electron Transport Chain 2. Intermembrane Space: Accumulation of protons 3. Matrix: containing enzymes for the Krebs Cycle
- 14. Overview Aerobic Cell Respiration
- 15. ATP balance
- 16. Vocab 8.2Vocab 2.8 Catabolic Anabolic Oxidation Reduction Redox reaction Phosphorylation Lysis ATP/ADP Decarboxylation ATP synthase Substrate level phosphorylation Oxidative phosphorylation Rapid oxidation Slow oxidation Glycolysis Pyruvate Cell respiration Anaerobic respiration Fermentation Alcoholic fermentation Lactic acid fermentation Aerobic respiration Homework
- 17. 2.8 8.2 Exercises 21-24, pg 103 Challenge Yourself, pg 364 Exercises 4-8, pg 368 More Homework
Editor's Notes
- There are four main stage in the breakdown of glucose during aerobic respiration: Glycolysis. The link reaction Krebs cycle Electron transport chain
- GLYCOLYSIS TAKE PLACE IN THE CYTOPLASM OF CELLS. Glycolysis does not need oxygen. It is the first stage of anaerobic respiration and it is, in fact, the only anaerobic stage. Iniatially the glucose is phosphorylated to make glucose phosphate. The phosphate comes from a molecule of ATP. Glucose phosphate is then phosphorilated to fructose bisphosphate using up another ATP. Fructose bisphosphate split into 2 molecules of glicerate-3-phosphate (3C) and the glicerate-3-phosphate is converted to piruvate. Hydrogen is removed and transferred to the hydrogen acceptor NAD. Enough energy is released at this stage to make two molecules of ATP. Important: Since 2 molecules of glicerate-3-phosphate are formed, there will be 2 molecules of NADH2 formed and 2x2=4 molecules of ATP So from 1 molecule of glucose, glycolysis produces the following: 2 molecules of ATP (4 ATPs are produce but 2 are used up) 2 molecules of NADH2 (reduced hydrogen acceptor) 2 molecules of Piruvate, which enter the link reaction in aerobic respiration.
- In the presence of Oxygen 3 things happen: The pyruvate is descarboxilated (a molecule of CO2 is removed) The pyruvate is dehydrogenated (a molecule of hydrogen is removed). The hydrogen is transferred to the acceptor NAD+ to form NAD+ + H+ The resulting acetate (2C) combines with coenzyme A (CoA) to form the 2C-molecule acetyl-Coenzyme A, which enters Krebs cycle. Since 2 molecules of piruvate are formed form each glucose molecule, there will be also 2 acetyl CoA molecules formed.
- Krebs cycle takes place in the matrix of the mitochondria and includes the following reactions> Acetyl Co-A combines with a 4-carbon compound (oxaloacetate) to form a six-carbon compound (citrate) A series of reactions take place where the ciitrate (6C) is both decarboxylated and dehydrogenated Carbon dioxide is released as a waste product and the hydrogen atoms are picked up by the hydrogen aceptor NAD and FAD (flavine adeninde dinucleotide) As a result, oxaloacetate (4C) is regenerated to combine with more acertyl coenzyme A. So, after one turn of the Krebs cycle, we have: 3 molecules of NADH 1 molecule of FADH 1 molecule of ATP 2 molecules of CO2 But, don’t forget that 2 molecules of Acetyl-CoA enter in the Krebs cycle for each molecule of glucose. So the cycle turns twice for each glucose molecule, so giving: 6NADH, 2FADH, 2ATPs, 4CO2
- The electron transport chain provides the means by which the energy from the hydrogen atoms removed from compounds in Krebs cycle, glycolysis and the link reaction can be used to make ATP. Oxygen is required for this final stage of aerobic respiration. The reactions take place in the inner membrane of the mitochondria. The electron transport chain involves a chain of carriers molecules along which hydrogen atoms and electrons are passed. The hydrogen atoms are passed on to other carrier molecules from the hydrogen carriers reduced NADH and FADH2.
- The hydrogen atoms split into hydrogen ions (H+) and electrons. The electrons are transferred along a series of electron carriers. The Hydrogen ions stay in solution in the space between the inner and outer membranes of the mitochondria. Finally, the electrons recombine with the hydrogen ions to form hydrogen atoms and are passed on to oxygen to form water. Oxygen is therefore the final electron acceptor. The transfer of electrons along the chain releases sufficient energy to make ATP from ADP+Pi.
- For each NADH entering at the chain, 3 molecules of ATP are made. And for each FADH, 2 molecules of ATP are made. The formation of ATP in this way is called oxidative phosphorilation.