Don’t you just love John Lennon?
I immensely enjoyed doing this blog even though it had its up and downs. I hope other people enjoy also.This learning tactic was great at retaining information,always keeping you on your feet thanks to our lecturer..Mr. Jason Matthews. Toodles people, finals here we come.=)
The TCA cycle is different from glycolysis in that it has no beginning or end. Where in glycolysis adding a given amount of a glycolytic intermediate would result in the synthesis of a certain amount(equal to) of number of moles of pyruvate, the addition of a given amount of an intermediate of the TCA cycle results in a greater amount than that of number of moles of pyruvate consumed. In the TCA cycle certain substrates and prouducts are formed catalyzed by enzymes. The steps can be followed from the diagram below.
Firstly the pyruvate is change into Acetyl CoA,these two substrates are oxalocacetate and Acetyl CoA produces citrate and CoA-SH this irrerversible reaction is catalysed by citrate synthase. It is followed by substrate citrate which produces Aconitate and this reaction that occurs here is called a dehydration reaction catalysed by Aconitase. Thirdly cis-Aconitate and water reacts to form Isocitrate which is catalyse by Aconitase. Here Isocitrate to product Oxalosuccinate which is catalysed by Isocitrate dehydrogenase produces in this oxidation reaction NADH. Oxalosuccinate reacts to form alpha Ketoglutarate and CO2 which is catalysed by Isocitrate dehydrogenase. a-ketoglutarate reacts to form Succinyl-CoA which is catalysed by oxidative decarboxylation,this stage would yield NADH and CO2. After this stage succinyl is catalysed by succinyl-CoA synthetasem,this reaction is called substrate level phosphorylation and produces Succinate. Here at this stage it there would be GDP-GTP because of the fact that there is a condensation reaction occurring . What also occurs is the Succinyl-CoA being hydrolysis for the reaction to be balanced to occur. Following is the Succinate which produces Fumurate and ubiquinol,this is catalysed by succinate dehyrogenase,here in this reaction it uses FAH where FAH->FADH2. Fumarate produces L-Malate which is catalysed by Fumarase. This is a hydration reaction and can be seen below. Lastly L-Malate produces the Oxaloacetate which is catalysed by Malate dehyrogenase,this reaction is reversible and it generates NADH.
Therefore all in all per glucose molecule in the TCA cycle :1 ATP(GTP) ,2 CO2, 3 NADH, 1 FADH2 are produced
IMAGE OF THE TCA CYCLE.
What happens after to pyruvate? Under anaerobic conditions fermentation occurs fermentation is the general term for such processes which extract energy but doesnot consume oxygen or change the concentrations of NAD+ or NADH.
Firstly there is the entry into the TCA cycle. This reaction is irreversible with the cofactors CoA-SH,NAD+,TPP lipoate,FAD,NADH. The enzyme that is used to catalyse this reaction is pyruvate dehydrogenase.
Secondly under anaerobic conditions there is the conversion of pyruvate to lactate. In mature red blood cells Eurocytes cells need to have NADH. The red blood cell converts pyruvate to lactate to regenerate NAD+. Glucose is converted to 2 NADH and the NAD+ needs to be regenerated this is done by converting the 2 pyruvate molecules to 2 lactate molecules. The enzyme used is lactate dehydrogenase and the reaction is reversible. In fermentation there is no net gain. No ATP is generated. When lactate is produced not enough oxygen is present,the acidification that results from ionization if the lactic acid in muscle and blood limits the length of time given for vigorous activity.
Lastly the final fate is pyruvate to ethanol.Ethanol results from the decarboxylation of pyruvate and the reduction of acetaldehyde. Yeasts and other organisms that produce ethanol use a two-step reaction sequence. First, pyruvate decarboxylase releases CO2 to make acetaldehyde. Then alcohol dehydrogenase transfers a pair of electrons from NADH to the acetaldehyde, resulting in ethanol.
Take a look its really helpful 🙂