Here computers do most of the data-handling. Highly sophisticated programs from the Internet can examine the nucleotide sequences of many genes, and deduce the amino acid sequences of proteins. Learning to use these programs needs hands-on practice in front of the screen. Microbiologists of the old school may deplore (= envy?) the limited amount of quantitative work that the researcher now has to do. In this chapter we shall consider some topics that still are feasible with pencil and paper and a bit of thought.

Composition of DNA

The discovery of DNA was reported by Friedrich Miescher in 1871. Understanding the detailed structure of the DNA molecule became very important after Avery and Macleod had shown that DNA was the material of the gene. Each of the two strands in a molecule of DNA is a linear polymer of units of 2-deoxyribose 5-phosphate. Every one of these deoxypentose units is linked to a purine base (adenine (A) or guanine (G)) or to a pyrimidine base (thymine (T) or cytosine (C)). The sequence in which these bases occur (on the chain of deoxypentose phosphate units) is the genetic code.