Q: What is the difference between DNA and RNA?

A: DNA contains all of the genetic information necessary to construct cells, to integrate them into an organism and to maintain them. RNA translates this information into specific instructions for the assembly of proteins, transmits the information outside the cell nucleus and helps to assemble them. Each DNA molecule contains hundreds of millions of atoms in a specific and unique sequence. The DNA molecule is shaped like a ladder twisted into a spiral, like a telephone cord. The rungs of the ladder are molecules called nucleotides; the rail of the ladder consists of alternating molecules of sugar and phosphate. There are four nucleotides, each of which is half of a complementary base pair. Each nucleotide fits into its mate on the opposite rail like two pieces of a jigsaw puzzle. When a cell reproduces a segment of the DNA ladder unzips. The base pairs separate and expose the nucleotides. Each exposed nucleotide attracts its complement from chemicals present in the cell nucleus. The result is two new ladders, each of which is identical to the original. At other times short sections of DNA unzip to expose a certain sequence of base pairs, called a gene. This is where RNA comes in. RNA is similar to DNA in some ways. Nucleotides in RNA are held together by sugars and phosphates. RNA differs from DNA in that each RNA molecule is only a single strand of nucleotides, and is much shorter. An RNA molecule is created by matching the sequence of exposed nucleotides on the unzipped DNA molecule. The RNA is an inverse copy of the gene, like a negative film image. Encoded in it is the information which will be decoded and translated to make the proteins which form the basis of life. Our physical being is an assemblage of thousands of proteins of various types. Structural materials like skin, claws, nails, bones, hair, muscles and the hard bodies of insects and shellfish are proteins. Enzymes are proteins, as are chemicals like insulin and hemoglobin. Proteins are the chemicals of life. The proteins and nucleotide sequence is slightly different for each individual. The types of proteins and the length of DNA are different for each species. But we share with all other people and all other forms of life the same set of amino acids, the same nucleotides and the same genetic code.

Richard Brill is assistant professor of science at Honolulu Community College where he teaches earth and physical science. Send questions to him at Honolulu Community College, 874 Dillingham Blvd., Honolulu, HI 96817 or email to rickb@hcc.hawaii.edu

DNA & RNA ©1995 Richard C. Brill