2 8.1.1 Comparison of Oxidation and Reduction Loss of hydrogen atomsEnergyGlucoseGain of hydrogen atomsOILRIG: Oxidation is losing electrons/protons; Reduction is gaining electrons/protons
3 8.1.1 Comparison of Oxidation and Reduction often associated with the release of energyReduction:often associated with the gain of energy
4 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 coenzymeIt’s Reduced to NADH when it picks up two electrons and one hydrogen ionNAD H NADH + H+FAD H FADH2Remember that 2H = 2 electrons and 2H+
5 Aerobic respiration process There are four main stage in the breakdown of glucose during aerobic respiration:Glycolysis.The link reactionKrebs cycleElectron transport chain
6 8.1.2 Outline the process of Glycolysis Glucose (6C)Glucose phosphate (6C)Fructose bisphosphate (6C)glicerate 3-phosphate(3C)Pyruvate (3C)ATPADP + Pi2 ADP + Pi2 ATPNAD+NADH + H +PHOSPORILATIONLYSISGLYCOLYSIS TAKE PLACE IN THE CYTOPLASM OF CELLS.Glycolysis does no need oxygen.It is the first stage of anaerobic respiration and it is, in fact, the only anaerobic stage.Iniatially the glucose is phosphorilated 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 ATPSo 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.OXIDATION&ATP FORMATION
7 8.1.3 Structure mitochondrion like in micrographs
8 8.1.4 Aerobic respiration: the link reaction Piruvate (3C) enters the matrix of the mitochondria from the cytoplasmAcetyl Coenzyme A(2C)Coenzyme APiruvate (3C)Acetate (2C)+CO2NAD+NADH + H +In the presence of Oxygen 3 things happen:The piruvate is descarboxilated (a molecule of CO2 is removed)The piruvate 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.Piruvate + CoA +NAD acetyl-CoA + CO2 +NADH + H+
9 8.1.4 Aerobic respiration: Krebs Cycle Acetyl Co-A combines with a 4-carbon compound (oxalacetate) to form a six-carbon compound (citrate)A series of reactions take place where the citrate (6C) is both decarboxylated and dehydrogenatedThe 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 of ATP.Krebs cycle take place in the matrix of the mitochondria and includes the following reactions>Acetyl Co-A combines with a 4-carbon compound (oxalacetate) to form a six-carbon compound (citrate)A series of reactions take place where the ciitrate (6C) is both decarboxylated and dehydrogenatedCarbon 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 NADH1 molecule of FADH1 molecule of ATP2 molecules of CO2But, 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, 4ATPs, 4CO2
10 The electron transport chain 8.1.4 Aerobic respiration:The electron transport chainThe final stage occurs in the inner membranes of mitochondria. This stage has two parts: an electron transport chain and ATP production by ATP synthaseThe 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.
11 8.1.5 Electron Transport Chain & Oxidative phosphorilation Chemiosmosis couples the electron transport chain to ATP synthesisNADH is the first carriers in the chain, it passes its hydrogen on to FAD. 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 recombines 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.
12 8.1.5 Oxidative phosphorilation & Chemiosmotic theoryMitochondria have a double membrane and the inner membrane is folded to form cristae. The cristae are lined with stalked granules, these stalked granules cotain ATP synthetase enzyme. The chemiosmotic theory provides a model to explain the synthesis of ATP in oxidative phosphorilation. The energy released by electron transport chain os linked to pumping hydrogen ions from the matrix into the space between the 2 membranes of the mitochondrion. This results in a higher concentration of hydrogen ions in the intermembrane space than in the matrix of the mitochondrion: an electrical electrochemical gradient is set up.The hydrogen ions pass back into the matrix through the stalked granules, along the electrochemical gradient. As they do so, their electrical potential energy is used to make ATP from ADP + Pi. ATP synthetase catalyses the reaction.
13 8.1.6 Relationship between structure of mitochondrion and its function Cristae: Large Surface Area for the Electron Transport ChainIntermembrane Space: Accumulation of protonsMatrix: containing enzymes for the Krebs Cycle