We began our exploration of organic chemistry by looking at functional groups, which are a useful way of classifying and studying organic molecules. We use the designation "R" for the collection of atoms other than those in the functional group we're discussing, in order to keep our attention on a particular group of atoms. We looked at several oxygen-containing functional groups, including alcohols, ethers, aldehydes, ketones, carboxylic acids, and esters.

We also looked at two nitrogen- containing functional groups: amines and amides. We finished our discussion of functional groups with those that contain sulfur or phosphorous.

Food energy molecules are organic, so we can use functional groups as a tool for studying their structure and function. One group of multi-functional organic molecules is the monosaccharides. Most monosaccharides are used for energy. Glucose and fructose, isomers with the formula C-6-H-12-O-6, are an important source of energy in most cells. Ribose and deoxyribose are used less often as an energy source, but they play an important role in the nucleotides that are combined to form RNA and DNA.

Fatty acids are nonpolar hydrocarbon chains with a carboxylic acid group at one end of the molecule. Saturated fatty acids contain only carbon-carbon single bonds, while unsaturated fatty acids have one or more carbon-carbon double bonds.

Amino acids contain an amino group, a carboxylic acid group, and one of 20 side chains, designated here as the R group. The side chains are either nonpolar, such as we see in alanine; polar, as in serine, or ionic, as in aspartic acid.

As mentioned earlier, pentose sugars are an important component of nucleotides. The other important components include one of the 5 nitrogenous bases, and a phosphate group.

Now that we've seen many different functional groups and learned about amino acids, let's explore the relationship between aspirin's structure and its biological activity in more detail. Many of the physical symptoms people take aspirin for, like pain or swelling, are caused by molecules called PROSTAGLANDINS. In the body, prostaglandin precursors are converted to prostaglandins by biological catalysts called enzymes. One of these enzymes has the amino acid SERINE in a critical position in its structure. Aspirin works by reacting with serine's alcohol-containing side chain, which converts the enzyme to an inactive form. Since this enzyme normally produces pain-causing prostaglandins, it can't do that anymore. The good news is that without prostaglandins, the pain stops and the swelling goes down, so you start to feel better soon after taking an aspirin!

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