10.1 Molecular Definition of a Gene

10.2 Chromosomal Organization of Genes and Noncoding DNA

10.3 Mobile DNA

10.4 Structural Organization of Eukaryotic Chromosomes

10.5 Morphology and Functional Elements of Eukaryotic Chromosomes

10.6 Organelle DNAs

► FIGURE 10-1 Overview of the structure of genes and chromosomes.

DNA of higher eukaryotes consists of unique and repeated sequences. Only -5% of human DNA encodes proteins and functional RNAs and the regulatory sequences that control their expression; the remainder Is merely spacer DNA between genes and Introns within genes. Much of this DNA, -50% In humans, is derived from mobile DNA elements, genetic symblots that have contributed to the evolution of contemporary genomes. Each chromosome consists of a single, long molecule of DNA up to -280 Mb in humans, organized Into increasing levels of condensation by the hlstone and nonhistone proteins with which It is Intricately complexed. Much smaller DNA molecules are localized In mitochondria and chloroplasts.

chloroplasts also contain DNA, probably evolutionary remnants of their origins, that encode essential components of these vital organelles.

In this chapter we first present a molecular definition of genes and the complexities that arise in higher organisms from the processing of mRNA precursors into alternatively spliced mRNAs. Next we discuss the main classes of eukary-otic DNA and the special properties of mobile DNA. We also consider the packaging of DNA and proteins into compact complexes, the large-scale structure of chromosomes, and the functional elements required for chromosome duplication and segregation. In the final section, we consider organelle DNA and how it differs from nuclear DNA. Figure 10-1 provides an overview of these interrelated subjects.

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