Metabolism II Flashcards
Link Reaction, TCA cycle, Oxidative Phosphorylation
How many molecules of Acetyl-CoA does the link reaction produce and why?
Produces 2 Acetyl-CoA for every 1 molecule of glucose, as 2 molecules of pyruvate are produced from glycolysis.
Where does the link reaction take place?
Link reaction begins in the cytosol, where pyruvate begins to be transported to the mitochondrial matrix by transmembrane transporters, where pyruvate is converted to acetyl-CoA under aerobic conditions to be used in TCA.
Link reaction equation:
Pyruvate + (NAD+) + CoA –> Acetyl-CoA + NADH + CO2 + (H+). *oxidative decarboxylation reaction + forming NADH
What is the PDC and what are its components?
Pyruvate dehydrogenase complex is responsible for the oxidative decarboxylation of pyruvate to form Acetyl-CoA in the mitochondrial matrix, and is composed of 3 enzymes; pyruvate dehydrogenase, dihydrolipoyl transacylase, dihydrolipoyl dehydrogenase.
Describe how PDC converts pyruvate to acety-CoA
- Decarboxylation, pyruvate combines with TPP and decarboxylated to form hydroethyl-TPP (rate limiting step)
- Oxidation, hydroxyethyl group on TPP is oxidised to form an acetyl group which is then attached to a lipoamide (deritive of lipoic acid, linked to side chain of lysine residue by amide linkage) resulting in energy rich thioester bond. Yeilds acetyllipoamide + carbanion of TPP.
- Energy rich thioester bond in acetyl group is transferred to CoA (CoA acts as carrier of Acyl groups) forming Acetyl CoA.
- Dihydrolipoamide is oxidised to lipoamide FAD is reduced to FADH2 which NAD+ accepts electrons from and produces FAD, NADH, H+.
Name all the intermediates of the TCA cycle.
- Citrate
- Isocitrate
- a-Ketoglutarate
- Succinyl CoA
- Succinate
- Fumerate
- Malate
- Oxaloacetate
Name all the enzymes used in the TCA cycle.
- Aconitase
- Isocitrate dehydrogenase
- a-Ketoglutarate dehydrogenase complex (a-KDC)
- Succinyl CoA synthase
- Succinate dehydrogenase
- Fumerase
- Malate dehydrogenase
- Citrate synthase
Name the inhibitors and promoters of the TCA cycle.
Inhibitors- ATP, Acetyl CoA, NADH, Succinyl CoA.
Promoters- ADP, Pyruvate
What are anaplerotic reactions and name some of the products of anaplerotic reactions from the TCA cycle.
Anaplerotic reactions are those that form intermediates of a metabolic pathway, such as glucose from oxaloacetate, fatty accids and sterols from citrate and glutamate from a-ketoglutarate.
What is oxidative phosphorylation and where does it occur?
Function is the oxidation. of NADH by O2 by 3 protein complexes, 2 mobile carries, cytochromes and iron-sulphur proteins in the inner mitochondrial membrane.
What are the redox products of the partial oxidation of glucose during glycolysis and TCA cycle?
24 [H+] reducing 10 NAD+ and 2 Ubiquinone to 10 NADH and 2 Ubiquinol.
Where does most of the energy of glucose stored?
Reduced NADH in the reaction NADH + (H+) + 1/2 O2 –> (NAD+) + H2O giving a DG= -220 KJmol-1.
Name the 3 protein complexes and 2 mobile carriers used to oxidise NADH.
PC= I- NADH dehydrogenase III- Cytochrome b/c1 complex IV- Cytochrome oxidase MC= 1- UQ= Ubiquinone 2- Cytc= Cytochrome c
What gets reduced when NADH gets oxidised?
1/2 O2 + 2H+ –> H2O
Difference between cytochrome a,b,c?
Differences distinguished by absorbance spectra. a,b heme is non covalently bound to protein. c, covalently bound.
