Question

All enzymes of TCA cycle are located in the mitochondrial matrix except one which is located in inner mitochondrial membranes in eukaryotes and in cytosol in prokaryotes. This enzyme is:
(a) Succinate dehydrogenase
(b) Lactate dehydrogenase
(c) Isocitrate dehydrogenase
(d) Malate dehydrogenase

Answer 1

Hint: TCA(Tricarboxylic acid) cycle occurs inside the mitochondrial matrix of eukaryotic cells and cytoplasm of prokaryotic cells. It is also called the Krebs cycle or Citric acid cycle.

Complete answer:
All enzymes of TCA cycle are located in the inner mitochondrial matrix except one which is located in inner mitochondrial membranes in eukaryotes and in cytosol in prokaryotes. This enzyme is Succinate dehydrogenase.
Succinate dehydrogenase participants both in TCA cycle and Electron transport system. In the TCA cycle, hydrogen atoms are removed from the fuel molecules (pyruvic acid) and are transferred to the carrier molecules, such as NAD for further processing in the Electron transport system.
TCA cycle starts with coenzyme A which transfers its 2-carbon acetyl group to the 4-carbon compound oxaloacetic acid forming a 6-carbon compound called Citric acid. This citric lose its one molecule of water changing into another 6-carbon compound cis-aconite acid by an enzyme called aconitase. CIS aconitic acid is converted into isocitric acid by utilising water. Iso-citric acid on oxidation gives oxalosuccinic acid in the presence of Isocitrate dehydrogenase. -Ketoglutaric acid is formed by the presence of an enzyme called decarboxylase. -ketoglutaric acid results in the formation of succinyl coA. Further, CoA splits off from succinyl coA and forms succinic acid. Succinic acid oxidized into fumaric acid in the presence of an enzyme called Succinate dehydrogenase.
In the Electron transport system, Succinate dehydrogenase derives electrons to complex II to reduce oxygen and form water. Due to three different iron-sulphur clusters and one covalently bound FAD, electrons pass from succinate through FAD and iron-sulphur centres before entering the Electron transport system.

So, the correct answer is ‘Succinate dehydrogenase’.

Note:
Succinate dehydrogenase is also called Market enzyme.
Succinate dehydrogenase is the component of Complex II.