Question

Structure of an Omega-3 Fatty Acid The omega-3 fatty acid docosahexaenoic acid (DHA, \(\left.22: 6\left(\Delta^{4,7,10,13,16,19}\right)\right)\) is the most abundant omega-3 fatty acid in the brain and an important component of breast milk. Draw the structure of this fatty acid.

Short answer

DHA has a 22-carbon chain with 6 double bonds at positions 4, 7, 10, 13, 16, and 19.

Step-by-step solution

Understand Fatty Acid Nomenclature

The notation "22:6(Δ^{4,7,10,13,16,19})" provides the chain length and the positions of the double bonds in the fatty acid. "22" indicates there are 22 carbon atoms, "6" indicates there are 6 double bonds.

Identify the Double Bond Positions

The positions provided in the parentheses (Δ^{4,7,10,13,16,19}) indicate the carbon numbers where each double bond is located, starting from the carbonyl end. These are at positions 4, 7, 10, 13, 16, and 19.

Draw the Basic Carbon Chain

Create a linear chain of 22 carbon atoms. Keep it straight initially to allow space for inserting double bonds.

Insert Double Bonds

Place double bonds at the specified positions along the carbon chain: between C4-C5, C7-C8, C10-C11, C13-C14, C16-C17, and C19-C20.

Ensure the Omega-3 Naming

Since it is an omega-3 fatty acid, ensure that the first double bond from the omega end (the opposite of the carbonyl end) appears at the third carbon when counting from that end.

Add Hydrogen Atoms

Attach hydrogen atoms in such a way that each carbon atom forms four covalent bonds, ensuring that the chain remains saturated except at the double bonds.

Key concepts

Docosahexaenoic Acid (DHA)

Docosahexaenoic Acid (DHA) is a key omega-3 fatty acid with significant importance in human health. It is primarily found in the brain, eyes, and heart. DHA plays a crucial role in cognitive and visual development, especially in infants, which is why it is often a component of prenatal supplements and included in baby formula.
Dietary sources of DHA include fish like salmon and mackerel, and it can also be derived from algae, making it accessible for vegetarians and vegans. Maintaining adequate levels of DHA is associated with various health benefits, including improved mental focus, reduced inflammation, and lower risk of chronic diseases.

Fatty Acid Nomenclature

Fatty acid nomenclature may initially seem complex, but it is based on a systematic method that conveys valuable information.

• Chain Length: The first number in the notation represents the total number of carbon atoms in the fatty acid. For DHA, this number is 22, indicating a 22-carbon atom chain.
• Double Bonds: The second number, found after the colon, indicates the number of double bonds present, which for DHA is 6.
• Double Bond Positions: The numbers following the delta (Δ) symbol show the specific carbon atoms where each double bond is located. In DHA, these are at positions 4, 7, 10, 13, 16, and 19, starting from the carbonyl end.

This method of naming allows scientists and health professionals to easily understand the structure and nature of various fatty acids, helping to communicate findings and recommendations efficiently.

Double Bond Positioning

Double bond positioning in fatty acids is a fundamental concept that influences the properties and classification of the molecule. In DHA, the positions of the double bonds are identified relative to the carbonyl end of the molecule, which is the functional group that distinguishes fatty acids.
In terms of molecular structure, double bonds introduce kinks due to the restricted rotation around these bonds, which affects how the molecules pack together. This, in turn, impacts the fluidity of cell membranes.
The omega-3 designation of DHA is determined by the location of the first double bond being at the third position from the omega end, which is opposite the carboxyl group. Such precise positioning is crucial for the biological roles these molecules play in the body.

Biochemical Structure Drawing

Drawing the biochemical structure of a fatty acid like DHA involves several systematic steps. Start with the linear carbon chain, which in DHA comprises 22 carbon atoms. Space these adequately to allow the inclusion of hydrogen atoms and double bonds. Next, locate the double bonds based on their positions given in the nomenclature, appearing at carbons 4-5, 7-8, 10-11, 13-14, 16-17, and 19-20.
For each of these positions, ensure that the atoms involved in the double bonds exhibit the typical bend in the carbon chain, which distinguishes unsaturated fatty acids. All carbon atoms should fulfill their tetravalency, having four bonds with adjacent carbons or hydrogens as necessary. This ensures the structure is chemically accurate and reflects the molecule's real-world biochemical behavior.