What structural feature do cis unsaturated fatty acids have?

What structural feature do cis unsaturated fatty acids have?

• A. Straight tails
• B. Kinks that cause tails to bend
• C. Longer tails
• D. Higher melting point

Answer: (B)

Cis unsaturated fatty acids have a kink in their hydrocarbon tail created by the cis double bond. In the cis arrangement, the hydrogens on the same side of the double bond push the chain to bend, so the tail isn’t straight. This bend prevents tight packing of the fatty acid tails, which makes fats more fluid and lowers their melting point compared with saturated fats that have straight tails. So the defining structural feature is the kink that causes the tails to bend. The other ideas aren’t defining traits: straight tails describe saturated fats, longer tails don’t define cis unsaturation, and a higher melting point would not occur because the kink actually lowers it.

Cis unsaturated fatty acids have a kink in their hydrocarbon tail created by the cis double bond. In the cis arrangement, the hydrogens on the same side of the double bond push the chain to bend, so the tail isn’t straight. This bend prevents tight packing of the fatty acid tails, which makes fats more fluid and lowers their melting point compared with saturated fats that have straight tails. So the defining structural feature is the kink that causes the tails to bend. The other ideas aren’t defining traits: straight tails describe saturated fats, longer tails don’t define cis unsaturation, and a higher melting point would not occur because the kink actually lowers it.