Question

note that in this phospholipid, the tail (at the bottom) includes one unsaturated hydrocarbon chain and one saturated hydrocarbon chain. also note that the head (at the top) contains 1) one full negative charge, and 2) oxygen (o) atoms that have partial negative charges. the \cartoon\ version of the molecule, on the right, is used a lot in the life sciences because it simplifies the structure but emphasizes two key structural elements: the hydrophilic head (here, a blue sphere) and the hydrophobic tail (yellow lines). you probably wont be surprised to learn that these structural elements play a key role in how phospholipids function in organisms.
fats contain highly electronegative oxygen atoms, which carry a partial charge. which of the following is the most logical explanation for why fats are not soluble in water?
the oxygen atoms in fats are less electronegative than the oxygen atoms in water, so carry less of a partial charge.
numbers and geometry: c - o and o - h bonds are very few in number compared with nonpolar bonds, and the few o atoms are \buried\ by hydrophobic groups.
if fats were soluble in water, they could not perform their various functions in organisms, starting with energy storage and metabolism.
each fatty acid found in a fat consists of a long hydrocarbon chain that ends in a carboxl group (cooh, or o = c - oh). why is \fatty acid\ an appropriate name?
\fatty\ refers to the long hydrocarbon chain; the carboxyl group acts as an acid by dropping a proton, just like the carboxyl groups in amino acids.
carbon can form a total of four covalent bonds, so the c in the carboxyl group of a fatty acid can form a c - c bond with the hydrocarbon chain.
fats vary in structure because they can contain more than one type of fatty acid, and because fatty acids vary in the length and saturation of their hydrocarbon chains.
why is \phospholipid\ an appropriate name?
the head region has a polar group that adds to the strongly hydrophilic nature of the phosphate group.
the two hydrocarbon chains that make up the tail can be long or short and saturated or unsaturated.
these molecules contain a phosphate group (\phospho\) and a hydrocarbon tail that does not interact with water (\lipid\).

Explanation:

• For the first question:
• Water is polar. For a substance to be soluble in water, it should have significant polar - like interactions. In fats, the non - polar hydrocarbon chains (which are abundant) "bury" the few polar \(C - O\) and \(O - H\) bonds. So, the overall molecule is non - polar and not soluble in water.
• For the second question:
• The long hydrocarbon chain gives the "fatty" part of the name. The carboxyl group (\(COOH\)) can donate a proton (\(H^{+}\)), which is the characteristic of an acid (similar to amino acids which have a carboxyl group that can act as an acid).
• For the third question:
• The word "phospho" refers to the phosphate group (\(PO_{4}^{3 -}\) related group in phospholipids) and "lipid" refers to the non - polar hydrocarbon tail (which does not interact with water, a key property of lipids).

Answer:

• First question: Numbers and geometry: \(C - O\) and \(O - H\) bonds are very few in number compared with nonpolar bonds, and the few \(O\) atoms are "buried" by hydrophobic groups.
• Second question: "Fatty" refers to the long hydrocarbon chain; the carboxyl group acts as an acid by dropping a proton, just like the carboxyl groups in amino acids.
• Third question: These molecules contain a phosphate group ("phospho") and a hydrocarbon tail that does not interact with water ("lipid").