Final answer:
Fatty acid synthesis primarily occurs in the cytoplasm and endoplasmic reticulum of cells, and mitochondria are involved in the transport of necessary substrates. The correct sites for fatty acid synthesis are the mitochondria, endoplasmic reticulum, and cytosol.
Step-by-step explanation:
The student asked to list three major sites for fatty acid synthesis. The process of fatty acid synthesis occurs primarily in the cytoplasm, the endoplasmic reticulum, and also involves transport mechanisms from the mitochondria. While fatty acids up to 16 carbons in length are typically synthesized in the cytoplasm using a fatty acid synthase complex, elongation of these fatty acids can occur in the endoplasmic reticulum and is catalyzed by enzymes known as elongases. The transportation of acetyl-CoA from the mitochondria to the cytoplasm is crucial for this process and can be mediated by molecules such as citrate and acetylcarnitine.
Because fatty acid synthesis involves the addition of two-carbon units to the growing chain, substrates such as malonyl-CoA are used for this purpose. This synthesis is highly energy-dependent, and the mitochondria play a crucial role by providing the necessary energy in the form of ATP. Hence, the correct answer to the student's question is b) Mitochondria, Endoplasmic Reticulum, Cytosol, as these are the major sites for fatty acid synthesis.