Lipids, nucleotides and sugars

Lipids are generally insoluble in water. The simplest are fatty acids: a carboxyl group attached to an R group, which may be a methyl, an ethyl or a longer chain of –CH2 groups (1 to 19 carbons).

Palmitic acid has 16 carbons and arachidonic acid 20, counting the carboxyl carbon in both.

Fatty acids are saturated when they have no double bond and unsaturated when they have one or more C=C double bonds.

Glycerol, trihydroxy propane, is another simple lipid. Fatty acids esterified with glycerol give monoglycerides, diglycerides and triglycerides.

Glycerides are called fats or oils depending on their melting point. Oils melt at a lower temperature, so an oil such as gingelly oil stays liquid in winter.

Phospholipids contain phosphorus and a phosphorylated organic compound. They are found in cell membranes; lecithin is an example. Neural tissue has lipids of more complex structure.

Some carbon compounds contain heterocyclic rings, such as the nitrogen bases adenine, guanine, cytosine, uracil and thymine.

A base attached to a sugar is a nucleoside (adenosine, guanosine, thymidine, uridine, cytidine). If a phosphate is also esterified to the sugar, it is a nucleotide (adenylic, guanylic, thymidylic, uridylic and cytidylic acid).

DNA and RNA are made of nucleotides only, and they act as genetic material. Sugars such as glucose (C6H12O6) and ribose (C5H10O5) are also among the small biomolecules.