Which fatty acid is not synthesized by man
**Core Concept**
The human body has the ability to synthesize certain fatty acids from acetyl-CoA and other precursors, but there are some essential fatty acids that cannot be produced endogenously. This is due to the absence of specific enzymes or pathways necessary for their synthesis.
**Why the Correct Answer is Right**
Linoleic acid (LA) is an essential fatty acid that cannot be synthesized by humans because it requires the enzyme delta-6-desaturase, which is not present in humans. This enzyme is necessary for the conversion of linoleic acid to gamma-linolenic acid (GLA), a precursor for the synthesis of arachidonic acid, prostaglandins, and other important eicosanoids. Humans can only obtain linoleic acid through the diet.
**Why Each Wrong Option is Incorrect**
**Option A:** Oleic acid is a monounsaturated fatty acid that can be synthesized by humans through the desaturation of stearic acid by the enzyme stearoyl-CoA desaturase.
**Option B:** Palmitic acid is a saturated fatty acid that can be synthesized by humans through the condensation of acetyl-CoA molecules by the enzyme acetyl-CoA carboxylase.
**Option C:** Stearic acid is a saturated fatty acid that can be synthesized by humans through the elongation of palmitic acid by the enzyme stearoyl-CoA desaturase.
**Clinical Pearl / High-Yield Fact**
Essential fatty acids like linoleic acid are crucial for maintaining healthy cell membranes, regulating inflammation, and supporting various physiological processes. Deficiencies in these fatty acids can lead to skin problems, impaired wound healing, and other health issues.
**Correct Answer: D. Linoleic acid**