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KREBS CYCLE. Krebs Cycle. Occurs in matrix Discovered by Sir Hans Krebs Acetyl-CoA enters the cycle and combines with a 4C compound called oxaloacetate to give a 6C derivative called Citrate. Krebs Cycle.
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Krebs Cycle • Occurs in matrix • Discovered by Sir Hans Krebs • Acetyl-CoA enters the cycle and combines with a 4C compound called oxaloacetate to give a 6C derivative called Citrate
Krebs Cycle • Citrate is decarboxylated (removal of CO2) and oxidised (breaking of a C-H bond in acetyl-CoA) in the presence of NAD+ to generate a 5C deravitive called α-ketoglutarate, NADH and CO2 • α-Ketoglutarateis again decarboxylated and reduced by FAD (FlavineAdenine Dinucleotide) and NAD+ to produce maleate, a 4C dertive, CO2, NADH and FADH2 (Reduced FAD).
Krebs Cycle • Malate is the 4C derivative • other 4C derivatives (succinyl-coa, succinate and fumarate ) are isomers of malate • Malate is then further oxidised in the presence of NAD+ back to oxaloacetate, ie, the starting 4C compound is regenerated along with another NADH molecule
Krebs Cycle • For every turn of the cycle the energetics of the individual reactions allow for the formation of GTP (Guanine Tri-Phosphate) which is regarded as an ATP molecule as well. • For every NADH generated 2.5 ATP is formed upon its oxidation in the ETC (Electron Transport Chain) • for every FADH2 generated 1.5ATP are formed • The net products per acetyl-CoA, per turn of the cycle = 1ATP, 1FADH2, 2CO2, 3NADH
Krebs Cycle • The net products per glucose (2 acetyl-CoA), per turn of the cycle = 2ATP, 2FADH, 4CO2, 6NADH • This translates to be • = 2 FADH2 (TCA) × 1.5 3 ATP • = 6 NADH (TCA) × 2.5 15 ATP • = 2 ATP per turn of glucose 2 ATP • = 2 net ATP from Glycolysis 2 ATP • = 2 NADH from Glycolysis × 2.5 5 ATP • = 2 NADH per glucose in link reaction × 2.5 5 ATP • TOTAL = 32 ATP projected to be produced, ranges to 38
Importance of Krebs Cycle • Brings about the degradation of macromolecules. 3C pyruvate broken down to CO2 • Provides the reducing power for the electron (hydrogen) transport system, produces pairs of H atoms which are ultimately used to provide energy to make ATP in oxidative phosphorylation • Interconversion centre-source of intermediate compounds used to make other substances such as a.a., f.a., chlorophyll
Electron Transport Chain • Also called respiratory chain • Means by which energy from the Krebs cycle in the form of H atoms is converted to ATP • Site- cristae of mitochondria. • Mechanism of oxidative phosphorylation where ATP is made from ADP and Pi in the presence of O2
Electron Transport Chain • On the cristae are embedded enzymes (ATP synthase), electron/hydrogen carriers, and proton channels (H+ channels). • These are positioned so that the reduced hydrogen carriers (NADH and FADH) produced in the matrix are made accessible to the ATP generating machinery on the cristae.
Electron Transport Chain • FADH and NADH provide the high energy electrons that were extracted from the chemical bonds of glucose, which are coupled to the production of ATP. • NADH enters the chain of electron carriers at a higher energy level than FADH • Hence, NADH produces approximately 1 more ATP. • NADH is oxidised firstly to NAD+ and an H+ ion is released to combine with O2 to produce water, where in the process 1 ATP is generated. • the high energy electrons from NADH are passed on to the next electron carrier in the chain.
Electron Transport Chain • The next carrier is FAD- it accepts the electron to become reduced as FADH or it enters already reduced as FADH • as the electrons are passed from one carrier to the next they constantly loose energy that is coupled to the production of ATP. • The electrons are passed to the other carrier which is a cytochrome protein with an iron center. The Fe3+ becomes reduced then to Fe2+ which passes its electrons to cytochrome oxidase with a copper center again draining the energy from the electron that is coupled to the production of ATP.
Electron Transport Chain • The Cu2+ center of the cytochrome oxidase is reduced upon accepting the electron to a Cu1+draining the energy of the electron to couple it to the formation of ATP • The Cu1+ center is again oxidised when O2 the final electron acceptor in the chain takes the electrons and combines it with H+ ions to produce water
Total ATP Produced Glycolysis 2ATP = 2ATP 2NADH2= 6ATP Link rxn 2NADH2 = 6ATP Krebs cycle 2ATP = 2ATP 2FADH2 = 4ATP 6NADH2 = 18ATP Total ATP = 38 mol for each glucose mol