**Core Concept**
Mammalian mitochondria are primarily known for their role in cellular respiration, including oxidative phosphorylation and fatty acid metabolism. While they contain their own DNA and ribosomes, their functions are largely centered on energy production and lipid metabolism, not protein synthesis.

**Why the Correct Answer is Right**
Mitochondria are involved in fatty acid oxidation (β-oxidation) in the matrix, which generates acetyl-CoA for the TCA cycle. They also contain mitochondrial DNA (mtDNA) and use it for replication and transcription, supporting DNA synthesis in this organelle. However, protein synthesis in mitochondria is limited to a small number of proteins, mainly for mitochondrial function, and occurs via mitochondrial ribosomes. The vast majority of cellular proteins are synthesized in the cytoplasm by cytosolic ribosomes. Thus, mitochondrial involvement in **protein synthesis** is minimal and not a primary function.

**Why Each Wrong Option is Incorrect**
Option A: Fatty acid synthesis occurs primarily in the cytoplasm (via fatty acid synthase), not in mitochondria. However, **fatty acid oxidation (β-oxidation)** — option C — *does* occur in mitochondria, so this option is misleading but not the correct choice here.
Option B: Mitochondria contain mtDNA and replicate it during mitochondrial biogenesis, so DNA synthesis occurs within them.
Option C: Fatty acid oxidation (β-oxidation) takes place in the mitochondrial matrix and is a key metabolic pathway.

**Clinical Pearl / High-Yield Fact**
Mitochondria are not sites of major protein synthesis; the cytosol is the primary location. Students often confuse mitochondrial function with cytoplasmic processes — remember: **"Mitochondria make energy, not proteins."**

✓ Correct Answer: D. Protein synthesis