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DNA is a two-stranded macromolecule composed of nucleotides. The order of nucleotides on one strand can be inferred from the order on the other, because the nucleotides are always coupled A to T, T to A, G to C and C to G. Thus since a strand of DNA is some sequence of 4 different types of letters, the DNA molecule can be thought of as a book of letters, where each letter can be encoded using 2 bits of information. The double-stranded structure of DNA both stabilizes it and allows it to be easily opened and copied.

Bioinformatics has come a long way since Watson and Crick’s discovery, and is emerging to stand as a field on its own, not as a combination of biology and computer science, in the 21st century.

B. DNA to RNA to Protein to Cell There is a natural cycle, diagramed below, which occurs in nature.

Figure 3. The various stages in the process of converting DNA to a functional organism

DNA holds the genetic information that each organism needs to live and reproduce. In humans, DNA is about 3x109 nucleotides long, and contains roughly 22,000 genes. DNA is stored within the nucleus of a cell. By a process known as transcription, DNA is converted to mRNA, which is a slightly different molecule and which will be discussed in more detail later. mRNA is then transported into the cell’s cytoplasm to be translated into a sequence of amino acids, which fold into a 3-D structure to become a functional protein. Proteins are main building blocks of life, and they perform most functions within a cell. These cells working together make up a living organism.

C. DNA and RNA

As described above, DNA is a two-stranded molecule composed of 4 different nucleotides, adenine (A), cytosine (C), guanine (G), and thymine (T), which are paired C—G and A—T. DNA has a double-helix shape in 3D. RNA is a single-stranded molecule similar to DNA, except that thymine is replaced by a different nucleotide, uracil (U).

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