Chapter 3: Cell Structure and Function

The protective surfaces of prokaryotic cells are explored in detail, including the peptidoglycan composition that differentiates gram-positive and gram-negative bacteria, along with accessory structures such as flagella and pili that facilitate movement and attachment. Biofilm formation is presented as a clinically significant phenomenon in which microorganisms develop resistance to antimicrobial agents. Central to cellular survival is the regulation of substance movement across membranes through passive mechanisms including simple diffusion, osmosis, and facilitated diffusion, as well as energy-dependent processes such as active transport pumps, endocytosis, and exocytosis. The chapter explains how cells generate and utilize energy through metabolic pathways controlled by enzymatic catalysts, whose function depends on temperature, pH, and the presence of inhibitors. Energy production is detailed through aerobic cellular respiration, comprising glycolysis, the citric acid cycle, and oxidative phosphorylation, supplemented by anaerobic fermentation and photosynthetic pathways in autotrophic organisms. Genetic information flow is described through the central dogma mechanism: DNA replication ensures accurate hereditary transmission, transcription converts genetic instructions into messenger RNA, and translation synthesizes proteins using codon recognition. Cellular division mechanisms vary by organism type, with prokaryotes employing binary fission for asexual reproduction and eukaryotes utilizing the cell cycle with mitosis for growth and meiosis for sexual reproduction and genetic recombination. The chapter concludes by examining the relationship between genotype and observable traits, the classification and effects of mutations ranging from point mutations to transposable elements, and the mechanisms of horizontal genetic transfer in bacteria including transformation, transduction, and conjugation that accelerate evolutionary adaptation and antibiotic resistance development.