Chapter 11: Biological Membranes and Transport: Lipid Bilayers, Membrane Dynamics, and Solute Transport

Section 11.1 explains how replication initiates at specific origin sites (oriC in E. coli), where initiator proteins like DnaA bind and destabilize the helix. This is followed by helicase (DnaB) unwinding the DNA, single-stranded binding proteins stabilizing the open strands, and topoisomerases relieving supercoiling stress. Section 11.2 outlines the role of primase in synthesizing RNA primers and the action of DNA polymerase III in leading and lagging strand synthesis. It explores the processivity of DNA polymerases, their requirement for a 3'-OH group, and the synthesis of Okazaki fragments on the lagging strand. DNA polymerase I is introduced as essential for removing RNA primers and filling in gaps. Ligase then seals nicks to create a continuous strand. Section 11.3 covers proofreading mechanisms via 3'→5' exonuclease activity and the importance of high fidelity in replication. Section 11.4 expands on eukaryotic DNA replication, describing multiple origins of replication and the roles of polymerases α, δ, and ε, along with PCNA, RPA, and the licensing system to ensure once-per-cell-cycle replication. Telomerase is discussed in detail, highlighting how it extends telomeres using an internal RNA template to prevent chromosome shortening. Section 11.5 addresses the regulation of replication initiation and termination, and Section 11.6 discusses clinical and experimental inhibitors of replication such as aphidicolin and AZT. The chapter concludes by emphasizing the orchestration of multiple enzymatic complexes in maintaining genomic integrity across all domains of life.