Practice question

Extended lag phase not caused by high density per se but by requirement for extensive macromolecular synthesis before replication can resume. Cells transferred from old, stationary, or differently composed medium lack enzymes for new carbon source utilization, transport permeases, central metabolic dehydrogenases, and contain degraded ribosomes, oxidized proteins, and damaged DNA. They must induce transcription of catabolic operons lac, mal via cAMP CRP, synthesize ribosomal proteins rps, rpl, produce tRNA, generate ATP via substrate level phosphorylation, repair chromosome via Uvr, Rec systems. If transferred to medium requiring enzymes absent previously, time required for de novo mRNA translation lengthens lag. Cold shock, osmotic shock, antibiotic exposure exacerbate lag as chaperones GroEL DnaK and proteases Clp needed. Conversely high inoculum quorum signals like autoinducer 2 can shorten lag by sharing metabolites. Therefore requirement for enzyme synthesis and repair explains why lag can last hours while population numbers appear unchanged despite intense metabolic remodeling inside cells preparing for division.