Chapter 6: How Cells Read the Genome: From DNA to Protein

The differences between prokaryotic and eukaryotic transcription are highlighted, including the presence of three RNA polymerases in eukaryotes and the elaborate processing steps required for eukaryotic mRNA, such as 5' capping, RNA splicing to remove introns, and 3' polyadenylation. Alternative splicing is introduced as a mechanism that enables a single gene to produce multiple proteins. The chapter also covers the variety of noncoding RNAs (ncRNAs), including rRNA, tRNA, snRNA, and miRNA, and their essential roles in RNA processing, gene regulation, and translation. Translation itself is explored in detail, showing how ribosomes read mRNA codons and pair them with the correct amino acids using tRNA molecules. Key stages such as translation initiation, elongation, and termination are discussed, with emphasis on the roles of initiation factors, elongation factors, and release factors. Post-translational modifications, such as phosphorylation and glycosylation, are noted as critical for functional protein maturation. Finally, the chapter explains how gene expression is tightly regulated at multiple levels—transcriptional, post-transcriptional, translational, and post-translational—allowing cells to respond to environmental cues and maintain homeostasis. This chapter provides a full-circle view of how the genome becomes the functional output of the cell, giving rise to the molecular machinery that drives all cellular processes.