In lipid biochemistry, why do unsaturated fatty acids tend to be liquid at room temperature?

Correct option is A

The correct answer is (a) The cis-double bonds introduce kinks, reducing van der Waals interactions.

• Cis-double bonds in unsaturated fatty acids create kinks in the hydrocarbon chains.

• These kinks prevent tight packing of the molecules, thereby reducing van der Waals interactions between them.

• As a result, less thermal energy is needed to keep them in a liquid state, unlike saturated fatty acids, which pack tightly and are usually solid at room temperature.

Information Booster:

• Saturated fatty acids: No double bonds; straight chains that pack tightly, leading to higher melting points.

• Unsaturated fatty acids: One or more double bonds (usually cis), causing bends and reducing intermolecular attractions.

• Example: Olive oil (rich in unsaturated fats) is liquid at room temperature; butter (rich in saturated fats) is solid.

• Van der Waals forces: Weak attractions between molecules; stronger in well-packed (straight) chains.

Additional Information (Why Other Options Are Incorrect):

• (B) Lower molecular weights: Not always true; unsaturated fatty acids can have similar or higher molecular weights than saturated ones.

• (C) Ionic bonds: Fatty acids do not form ionic bonds in biological systems; they are primarily held together by hydrophobic interactions.

• (D) Increased molecular symmetry: Cis-double bonds reduce symmetry, making packing more difficult, not easier.