Question

Why are linoleate and linolenate considered essential fatty acids? What step in production of polyunsaturated fatty acids are mammals unable to perform?

Short answer

Linoleate and linolenate are essential because mammals cannot introduce double bonds beyond the 9th and 10th carbon positions, making ω-3 and ω-6 desaturation impossible.

Step-by-step solution

Define Essential Fatty Acids

Essential fatty acids are fatty acids that humans and other mammals must obtain through diet because they cannot be synthesized by the body.

Identify Linoleate and Linolenate

Linoleate, or linoleic acid, is an omega-6 fatty acid, and linolenate, or alpha-linolenic acid (ALA), is an omega-3 fatty acid. Both are essential fatty acids.

Explain Why They Are Essential

Linoleate and linolenate are considered essential because mammals lack the necessary enzymes to synthesize them. More specifically, mammals cannot introduce double bonds into fatty acids beyond the carbon 9 and 10 positions.

Detail the Missing Step in Polyunsaturated Fatty Acid Production

Mammals are unable to perform desaturation at the ω-3 (omega-3) and ω-6 (omega-6) positions. This means they cannot insert double bonds between the third and fourth or between the sixth and seventh carbons from the methyl end of the fatty acid chain.

Key concepts

linoleate

Linoleate, also known as linoleic acid, is an omega-6 fatty acid. This means that its first double bond is located at the sixth carbon from the methyl end of the fatty acid chain.
Linoleate is essential because our bodies cannot synthesize it on their own.
We primarily obtain linoleate through dietary sources like vegetable oils, nuts, and seeds.
Linoleate plays a crucial role in cellular functions and is essential for producing other important omega-6 fatty acids.
Without sufficient intake of linoleate, our cell membranes, brain functions, and growth could be compromised.

linolenate

Linolenate, or alpha-linolenic acid (ALA), is an omega-3 fatty acid. Its first double bond is situated at the third carbon from the methyl end of the fatty acid chain.
Similar to linoleate, linolenate is an essential fatty acid because our bodies lack the enzymes needed to produce it on their own.
Rich dietary sources of linolenate include flaxseeds, chia seeds, walnuts, and fish oils.
Linolenate is crucial for maintaining heart health and plays a key role in brain function and development.
Consuming enough linolenate can help reduce inflammation and may also lower the risk of chronic diseases like heart disease.

polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their carbon chain.
Both linoleate and linolenate fall into this category due to their multiple double bonds.
PUFAs can be further classified into omega-3 and omega-6 fatty acids, depending on the location of the first double bond.
These fatty acids are liquid at room temperature and are considered healthier compared to saturated fats, which have no double bonds.
PUFAs are important for various bodily functions, including inflammatory response, blood clotting, and the development of brain and eye tissues.

desaturation

Desaturation is a biochemical process where enzymes introduce double bonds into fatty acid chains.
In mammals, this process is limited by the absence of certain enzymes. Specifically, mammals cannot introduce double bonds beyond the carbon 9 and 10 positions from the carboxyl end.
This inability to desaturate at the ω-3 (omega-3) and ω-6 (omega-6) positions means that essential fatty acids like linoleate and linolenate must be obtained through diet.
The desaturation step is key to producing longer-chain polyunsaturated fatty acids, which are critical for various physiological functions.
Without this capability, the metabolic flexibility of humans and other mammals is constrained, necessitating dietary sources to fulfill these essential roles.