Question

Which of the following is true for the TCA cycle in eukaryotes?
A. Takes place in mitochondria
B. Produces no ATP
C. Takes place in Golgi complex
D. Independent of the electron transport chain

Answer 1

Hint: The word eukaryotic refers to an organism that consists of a cell in which the nucleus is enclosed in a nuclear envelope. Typically, membrane-bound cell organelles like mitochondria and Golgi complex are found in the cell of eukaryotes. The term TCA represents the tricarboxylic acid cycle.

Complete answer: A series of chemical reactions which involves the release of energy by oxidizing acetyl-CoA which is derived from fats, carbohydrates, and proteins is called a tricarboxylic acid cycle (TCA). This process is used by all aerobic organisms to release the energy stored within them. TCA cycle provides certain amino acids and reduces agents like NADH which are used in other chemical reactions. The tricarboxylic acid cycle takes place in the matrix of mitochondria in eukaryotes. The TCA cycle is completed in ten steps. Each molecule of glucose requires two turns of the Krebs cycle.
Step1. Aldol condensation of oxaloacetate and acetyl-CoA in presence of enzyme citrate synthase produces citrate and CoA-SH.
Step2. Citrate is dehydrated in presence of aconitase to form cis-Aconitate and water molecule.
Step3. Cis-Aconitate is hydrated to form isocitrate using aconitase.
Step4. Oxidation of isocitrate with NAD+ produces oxalosuccinate and NADH.
Step5. Oxalosuccinate undergoes decarboxylation to form α-ketoglutarate with the help of enzyme isocitrate dehydrogenase.
Step6. Oxidative decarboxylation of α-ketoglutarate along with NAD+ and CoA-SH forms succinyl-CoA, NADH, carbon dioxide, and hydrogen atom using enzyme α-ketoglutarate dehydrogenase.
Step7. Phosphorylation of succinyl-CoA with GDP produces succinate, CoA-SH, and GTP in presence of enzyme succinyl CoA synthetase.
Step8. Oxidation of succinate with ubiquinone produces fumarate and ubiquinol. The enzyme used is succinate dehydrogenase.
Step9. Hydration of fumarate produces malate using enzyme fumarase.
Step10. Malate is oxidized to form oxaloacetate, NADH, and hydrogen atom.
So, option A is the correct option.

Note: Tricarboxylic acid cycle (TCA) is also called a citric acid cycle (CAC) or Krebs cycle. TCA cycle takes place in the cytosol of prokaryotic cells as they lack membrane-bound organelles. Products obtained after completion of two rounds of Krebs cycle are two GTP, two ubiquinol, six NADH, and four molecules of carbon dioxide.