#log phase

Animal Tissue Culture 3

Cell viability during log phase is approximately:

Exponential log phase represents period of maximal health for mammalian cultures. Under optimal conditions of adequate nutrients, pH maintained at 7.2-7.4 by CO2-bicarbonate buffering, temperature 37°C, and absence of waste accumulation, trypan blue exclusion tests reveal membrane intact viable cells at 90-100% because apoptotic signaling minimal, caspase-3 inactive, mitochondrial membrane potential high as indicated by JC-1 aggregation. Mitochondrial succinate dehydrogenase activity robust leading to efficient reduction of tetrazolium salts in MTT assay. Cells display high cloning efficiency

Ref: Freshney Ch.18 Viability during log 90-100%; ATCC Cell Viability trypan blue exclusion exponential phase near maximal.

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Animal Tissue Culture 3

The phase of cell growth most suitable for drug testing is:

Pharmacological testing and chemosensitivity evaluation are most predictive during logarithmic exponential growth phase when cell population is actively cycling, metabolically robust, and homogeneous. During lag, cells are still recovering and fraction in S phase low, causing underestimation of antimetabolite efficacy. In log phase, DNA synthesis enzymes including topoisomerase II, thymidylate synthase, and kinases targeted by many drugs are highly expressed, mitochondrial activity high, ATP levels stable. Dose-response curves generated in this window show reproducible IC50 values. Plateau or

Ref: Freshney Ch.21 Drug testing log phase; NIH Assay Guidance Manual 2021 Chemosensitivity assays log phase optimal viability.

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Microbial Physiology

In the log phase, bacterial cell numbers increase by a factor of:

Balanced exponential growth implies each cell divides into two, so number after one generation doubles. In log phase cultures specific growth rate constant, generation time minimal, cells divide asynchronously but average population doubling per generation time. Starting N0, after n generations N equals N0 times two to n. Therefore per generation increase factor exactly two, not one meaning no growth, nor four or eight which would imply multiple fission or formation of tetrads and octads seen in some cocci Sarcina but not typical rods Escherichia coli bacilli dividing by binary transverse fiss

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Log phase - Cell number doubles factor 2.

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Microbial Physiology

Which phase is characterized by exponential bacterial growth?

Log phase also termed exponential phase represents balanced growth state where every cellular constituent doubles at identical specific rate. Under saturating nutrients and aeration, DNA replication initiates synchronously via DnaA ATP activation at oriC, elongation by PolIII, segregation by MukBEF SMC complex, and cytokinetic ring FtsZ with FtsA ZipA divides cells with constant interdivision time. Specific growth rate mu maximal, defined by mu equals ln2 over generation time g. Equation dN over dt equals mu N integrated yields N equals N0 times e to mu t, producing straight line on semi-log p

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Exponential phase and balanced growth.

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Microbial Physiology

During the log phase, bacterial cells:

Logarithmic phase also termed exponential phase reflects balanced growth where all cellular constituents increase in constant proportion and cells divide at maximal specific rate mu max set by genotype and environment. Biomass, protein, RNA, DNA and numbers double at exact constant generation time. DNA replication precisely matches division rate, ribosome content peaks up to 70 percent dry weight, peptidoglycan precursor synthesis via Mur enzymes operates maximally, and transcription of glycolysis and TCA cycle remains high while alarmone ppGpp stays low. Plotting log colony forming units vers

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 4: Log Phase and Exponential Growth Dynamics.

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