Chapter 14: Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway: Regulation and Energy Balance

Section 14.1 introduces chromosomal architecture, highlighting the distinction between bacterial chromosomes—typically circular, compacted via supercoiling—and eukaryotic chromosomes, which are linear and organized within chromatin. Eukaryotic chromatin is described as a hierarchical structure of DNA wrapped around histone proteins to form nucleosomes, further folded into higher-order structures. Histone variants and post-translational modifications such as acetylation and methylation are presented as key regulators of chromatin accessibility and gene expression. Section 14.2 discusses genome organization, distinguishing between coding regions (exons) and noncoding regions (introns, regulatory elements, repetitive sequences). It explores the paradox of genome size versus gene content, emphasizing the role of transposable elements, satellite DNA, and noncoding RNAs in shaping genome architecture. Section 14.3 focuses on gene families and the evolution of genomes, showing how gene duplication, exon shuffling, and horizontal gene transfer contribute to genetic diversity and complexity. Section 14.4 presents mechanisms of gene regulation in both bacteria and eukaryotes. Prokaryotic operons such as lac and trp are introduced to illustrate transcriptional control through repressors, activators, and feedback loops. In eukaryotes, gene expression is modulated via chromatin remodeling complexes, enhancers, silencers, transcription factors, and epigenetic modifications. The chapter also emphasizes long-range regulatory interactions and the role of nuclear architecture in gene control. Section 14.5 discusses chromosome dynamics during the cell cycle, including replication origins, centromeres, telomeres, and mitotic condensation. The chapter concludes by linking gene and chromosomal structures to genetic variation, regulation, and evolutionary processes, setting the foundation for understanding how genomic information is organized, maintained, and expressed in cells.