In our study, we focused on the conceptual understanding of the concepts and processes presented in the first lectures of an introductory course in cellular biology for biology majors. The study topic we considered was, "the structure of DNA and the functions of nucleotides". One hundred and eighteen students were asked to prepare concept maps from a list of twenty given concepts. Analysis of these maps has shown a compartmentalization into two major groups of concepts. The most frequent concepts were from the genetic aspect, while frequencies of concepts from the energetic aspect were comparatively low. Many students did not recognize that molecules like ATP or GTP are simply nucleotides. Other interesting misconceptions concerned the concepts of nucleic acids, purines and pyrimidines. One of the advantages of using the concept map technique was that it encouraged the instructor to start using maps as a graphic instructional tool, summarizing his lectures. In addition, the need to select twenty concepts and arrange them in a map forced him to go over his lectures and reconsider whether or not these concepts should have been selected for instruction. (Contains 5 figures and 2 tables.)