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 Citrate is decarboxylated (removal of CO 2 ) 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 CO 2 α-Ketoglutarate is again decarboxylated and reduced by FAD (Flavine Adenine Dinucleotide) and NAD + to produce maleate, a 4C dertive, CO 2, NADH and FADH 2 (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 FADH 2 generated 1.5ATP are formed The net products per acetyl-CoA, per turn of the cycle = 1ATP, 1FADH 2, 2CO 2, 3NADH

Krebs Cycle The net products per glucose (2 acetyl-CoA), per turn of the cycle = 2ATP, 2FADH, 4CO 2, 6NADH This translates to be = 2 FADH 2 (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 P i in the presence of O 2

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 O 2 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 Fe 3+ becomes reduced then to Fe 2+ 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 Cu 2+ center of the cytochrome oxidase is reduced upon accepting the electron to a Cu 1+ draining the energy of the electron to couple it to the formation of ATP The Cu 1+ center is again oxidised when O 2 the final electron acceptor in the chain takes the electrons and combines it with H + ions to produce water

Electron Transport Chain

Total ATP Produced Glycolysis2ATP = 2ATP 2NADH2= 6ATP Link rxn 2NADH2 = 6ATP Krebs cycle2ATP = 2ATP 2FADH2 = 4ATP 6NADH2 = 18ATP Total ATP = 38 mol for each glucose mol