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Chemistry Of Life
Describe how the presence of double bonds in unsaturated fatty acids affects the physical properties of a lipid at room temperature.
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Double bonds cause kinks in the hydrocarbon chain, which prevent unsaturated fatty acid molecules from packing tightly together. The weaker intermolecular interactions mean less energy is needed to separate the molecules, so unsaturated lipids tend to be liquid at room temperature rather than solid.
Predict the effect on the melting point of a fat molecule if one of its saturated fatty acid tails were replaced with a polyunsaturated fatty acid tail containing three double bonds?
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The melting point would decrease. The polyunsaturated tail introduces multiple kinks, which disrupts the tight packing of the fatty acid chains. With less orderly packing and weaker intermolecular interactions, the fat transitions from solid to liquid at a lower temperature.
Describe two functions of fats in living organisms.
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Fats store energy in their many carbon–hydrogen bonds, providing a concentrated fuel reserve for the organism. In some mammals, subcutaneous fat also provides insulation that helps maintain body temperature in cold environments.
Explain how the amphipathic nature of phospholipids leads to the formation of a lipid bilayer in an aqueous environment?
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Phospholipids have hydrophilic phosphate heads and hydrophobic fatty acid tails. In water, the hydrophobic tails are repelled by the aqueous surroundings, so they orient inward, away from water, while the hydrophilic heads face outward toward the water on both sides. This spontaneous arrangement produces a bilayer that acts as a selectively permeable barrier.
Predict what would happen to the structural stability of an animal cell membrane if cholesterol were removed?
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Without cholesterol, the membrane would lose its ability to moderate fluidity. At higher temperatures, the membrane would become excessively fluid because nothing would restrict phospholipid movement. At lower temperatures, the membrane could become too rigid because cholesterol normally prevents tight packing of phospholipid tails. Overall, the membrane would be less stable and less able to maintain consistent function across a range of temperatures.