Structure and Function of Biological Macromolecules

AP Biology· difficulty 3/5

A food chemist analyzes two fats: one is solid at room temperature (butter) and the other is liquid (olive oil). Both contain triglycerides composed of fatty acids similar to those drawn. The chemist wants to predict which sample contains more of each type of fatty acid.

COOH Saturated tail (no C=C) CH3 COOH Unsaturated tail (has C=C, kinks) CH3

Why does the unsaturated fatty acid (lower chain) tend to make a fat liquid at room temperature?

  • A

    Double bonds increase polarity, dissolving the fat in water

  • B

    Unsaturated chains form covalent bonds with each other

  • C

    It contains more hydrogen, raising the melting point

  • D

    Kinks at C=C double bonds prevent tight packing, weakening intermolecular forces

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Explanation

Cis double bonds introduce kinks that keep chains apart; weaker van der Waals attractions lower the melting point so the fat is liquid at room temperature.

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