Question

5. FA monomers indirectly interact via covalent bonds with other molecules to form lipid/fat polymers. Explain what this means, and why an additional molecule must be involved. Also describe the interaction that does occurs between FA tails, and why this interaction occurs; compare these interactions in saturated and unsaturated FAs.

Answer 1

A fatty acid monomer, consists of one carboxyl group at the end of a linear hydrocarbon containing at least four carbon atoms.Fatty acid monomers are not directly bonded to each other in polymer chains. They indirectly interact via covalent bonds with other molecules to form lipid polymers.

Process for connecting two fatty acid monomers together is called dehydration synthesis . Dehydration synthesis reactions in lipids form an ester linkage between the carboxyl group of a fatty acid and the hydroxyl group of an alcohol monomer such as glycerol. Thus they form lipid polymers . Two monomer molecules are covalently bonded to each other, with the loss of a water molecule and each monomer contributes part of the water molecule that is released during the reaction.

During this covalent bond formation, three water molecules are released and they may be similar or dissimilar. These fats are also called triglycerides because they have three fatty acids. Dehydration synthesis yields a fat molecule with three fatty acid tails bound to the glycerol backbone via ester linkages.

The three fatty acid tails may be identical or different from each other.

When the hydrocarbon chain has single bond , between the molecules , they are saturated. When the hydrocarbon chain has a double bond, the fatty acid is said to be unsaturated.

Saturated fatty acids tails are straight, so fat molecules with fully saturated tails can pack tightly against one another and it results in fats that are solid at room temperature. Eg : butter

cis-unsaturated fatty acid tails are bent due to the cis double bond. This makes it hard for fat molecules with one or more cis-unsaturated fatty acid tails to pack tightly.Therefore fats with unsaturated tails tend to be liquid at room temperature. Eg : oils