Practice question

Prokaryotes comprise bacteria and archaea lacking nucleus defined by nuclear envelope and possessing simpler architecture optimized for rapid division. They contain cell envelope with plasma membrane of phosphoglycerides and hopanoids, peptidoglycan wall providing shape and protection against turgor, nucleoid region where single circular chromosome typically 1-6 megabases supercoiled and organized by histone-like proteins HU, Fis, SMC condensins occupies cytoplasm without separation, and 70S ribosomes for coupled transcription translation. RNA species messenger, transfer, and ribosomal exist transiently. Metabolic processes such as aerobic respiration and photosynthesis occur across plasma membrane or intracytoplasmic membranes where electron transport components quinones, cytochrome bc1, cytochrome oxidase generate proton motive force for ATP synthase. Mitochondria, organelles bounded by outer membrane with VDAC porins and inner membrane with cristae housing respiratory complexes I-V, TCA cycle enzymes in matrix, and own circular mitochondrial DNA encoding 13 respiratory proteins, are absent in prokaryotic cells. Evolutionary theory traces mitochondria to endosymbiosis of alpha-proteobacteria engulfed by proto-eukaryote, providing compartmentalization in eukaryotes absent in prokaryotes which rely on membrane invaginations rather than dedicated powerhouses.