Describe the role of DNA in the nucleus of a cell, explaining how it contains the genetic code for determining the structure and function of organisms. Discuss the organization of DNA into chromosomes, the composition of chromosomes with segments known as genes, and the significance of genes as the basic units of heredity transferred from parent to offspring. Additionally, elucidate how DNA carries the genetic code through triplet codons for protein assembly, and mention the shared genetic code among organisms with diversity arising from the differing order of codons. Lastly, touch upon the non-protein-coding functions of some DNA segments, including regulatory and structural roles, while acknowledging that the functions of certain segments remain unknown.