Given below is the diagrammatic representation of one of the categories of small molecular weight organic compounds in the living tissues. Identify the category shown and the one blank component X in it:
| 1. | Category: Cholesterol; Component: Guanine |
| 2. | Category: Amino acid; Component: NH2 |
| 3. | Category: Nucleotide; Component: Adenine |
| 4. | Category: Nucleoside; Component: Uracil |