Link reaction and Krebs cycle 0.0 / 5 ? BiologyCellular processesA2/A-levelAQA Created by: HindleycCreated on: 04-11-18 19:54 First step of link reaction Pyruvate is actively transported across the mitochondrial membrane into the matrix (small enough to get through) 1 of 19 Step 2 Pyruvate is oxidised and decarboxylated to Acetate. 2 of 19 What happens in this process pyruvate loses a carbon dioxide molecule and 2 hydrogen molecules 3 of 19 What are hydrogens accepted by? NAD to from reduced NAD 4 of 19 step 3? 2 carbon Acetate molecule now combines with coenzyme A to form a molecule called Acetyl coenzyme A 5 of 19 Overall steps? Pyruvate- Acetate by losing CO2 and 2H that combines with 2NAD to form 2NADH. Acetate+ coenzyme A= Acetyl coenzyme A 6 of 19 Notes? This happens twice after glycolysis because 2 pyruvate molecules are produced therefore Krebs cycle happens twice too. 7 of 19 Where Krebs cycle? Matrix of mitochondria 8 of 19 What does cycle involve? Series of redox reactions to produce a single molecule of ATP (per acetyl coenzyme A) (substrate level phosphorylation) reduced FAD and reduced NAD 9 of 19 What is there also a series of? Decarboxylation reactions resulting in the release of carbon dioxide. 10 of 19 Step 1 4c oxaloacetic acid combines with 2c Acetyl coenzyme A producing citric acid 6c and coenzyme A. 11 of 19 Step 2 Citric acid is decarboxylated twice losing 2 carbons (CO2) 12 of 19 Step 3 Reduced FAD, NAD and 2NAD so citric acid oxidised -redox rxn removing Hydrogen and reducing coenzymes 13 of 19 step 4 Substrate level phosphorylation- phosphate from substrate combines with ADP forming ATP 14 of 19 How is this different to oxidative phosphorylation? Phosphate derived from chemicals in cycle 15 of 19 step 5 Substrate (citric acid) regenerated to oxaloacetic acid 16 of 19 Products? Reduced coenzymes FAD and NAD. ATP molecule, 2 molecules of CO2 17 of 19 Summary 2 decarboxylations, 4 oxidations of citric acid, 1 molecule through substrate level phosphorylation 18 of 19 diagram Oxaloacetic acid- Citric acid by 2c acetyl coA- CoA so add 2 c. Citric acid- oxaloacetic acid by losing 2 co2, NAD, 2NAD, FAD,ATP 19 of 19
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