TCA Cycle—Organelle Location in Eukaryotes In a eukaryotic cell, the enzymes of the tricarboxylic acid (TCA) cycle are predominantly located in the:

Introduction / Context:
The TCA cycle is the hub of aerobic metabolism, linking carbohydrate, lipid, and amino acid catabolism. Correctly assigning its location helps understand compartmentalized control and the coupling to oxidative phosphorylation.

Given Data / Assumptions:

• Eukaryotes segregate metabolic pathways by organelle.
• Respiratory chain resides in the inner mitochondrial membrane; ATP synthase uses the proton gradient generated there.

Concept / Approach:
In eukaryotes, TCA enzymes are mitochondrial, primarily in the matrix (with succinate dehydrogenase embedded in the inner membrane). Therefore, the correct organelle for the TCA cycle is the mitochondrion, not nucleus, plasma membrane, or lysosomes.

Step-by-Step Solution:

Verification / Alternative check:
Electron micrographs and organelle fractionation consistently localize these enzymes to mitochondria.

Why Other Options Are Wrong:

• Nucleus/lysosomes/plasma membrane: do not house the TCA cycle.
• Cytosol: hosts glycolysis, not the mitochondrial TCA reactions.

Common Pitfalls:
Conflating glycolysis (cytosolic) with TCA (mitochondrial) steps.

Final Answer:
Mitochondria