Mitochondrial matrix contents — Which of the following are found within the mitochondrial matrix of eukaryotic cells?

Introduction / Context:
The mitochondrial matrix is the innermost compartment enclosed by the inner mitochondrial membrane. It houses critical components for energy metabolism and mitochondrial gene expression. Recognizing its contents helps connect structure to function in cellular respiration and biosynthesis.

Given Data / Assumptions:

• Mitochondrial DNA (mtDNA) resides in nucleoids within the matrix.
• Matrix ribosomes (mitoribosomes) translate mtDNA-encoded proteins.
• Key enzymes of the tricarboxylic acid (TCA) cycle and parts of fatty acid oxidation localize in the matrix.

Concept / Approach:
Each listed item is a known matrix resident. The TCA cycle enzymes (e.g., citrate synthase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, malate dehydrogenase) function in the matrix; β-oxidation steps in many eukaryotes also involve matrix enzymes; mtDNA and mitoribosomes enable organelle-encoded protein synthesis in situ.

Step-by-Step Solution:

Verification / Alternative check:
Biochemical fractionation of mitochondria yields matrix fractions enriched in the above constituents; electron micrographs show dense matrix with nucleoids and ribosomes.

Why Other Options Are Wrong:

Common Pitfalls:
Forgetting that succinate dehydrogenase (Complex II) is embedded in the inner membrane while catalyzing a TCA step; most other TCA enzymes are matrix soluble.

Final Answer:
All of these.