Q.42 Determine the correctness or otherwise of the following Assertion (a) and the Reason (r).
Assertion: In synchronous culture, majority of the cells move to next phase of the cell cycle simultaneously.
Reason: Synchronous culture could be obtained by starving cells for essential nutrient components.
(A) both (a) and (r) are true and (r) is the correct reason for (a)
(B) both (a) and (r) are true but (r) is not the correct reason for (a)
(C) (a) is true but (r) is false
(D) (a) is false but (r) is true
Correct Answer: (A) Both (a) and (r) are true and (r) is the correct reason for (a)
In synchronous culture, all cells progress through cell cycle phases (G1→S→G2→M) simultaneously due to physical/chemical synchronization. Nutrient starvation arrests cells at G0/G1 (serum deprivation) or S-phase (thymidine block); replenishment triggers uniform division.
Option Analysis
-
(A): Correct. Synchronous cultures show >90% cells in single phase (flow cytometry validation); nutrient starvation induces G1 arrest via cyclin D/CDK4/6 inhibition, directly causing population synchrony.
-
(B): Incorrect. Nutrient starvation directly creates synchrony by halting progression until nutrient restoration.
-
(C): Incorrect. Reason true—essential amino acid/nitrogen starvation synchronizes yeast/bacteria at Start/G1 checkpoint.
-
(D): Incorrect. Assertion true; synchronous cultures enable precise growth rate (μ) vs time analysis.
Synchronous culture nutrient starvation synchronizes microbial populations for cell cycle analysis, forming Q.42 assertion-reason core testing biochemical engineering growth kinetics fundamentals.
Synchronization Mechanisms
Nutrient Starvation (Induction): Amino acid deprivation → uncharged tRNA → GCN2 kinase → eIF2α phosphorylation → global translation block at G1. Nitrogen starvation → TORC1 inhibition → autophagy induction. Restoration triggers exponential division wave.
Cell Cycle Progression:
t=0h: 95% G1 arrest (2N DNA)
t=2h: S-phase entry (DNA replication)
t=4h: G2/M peak (4N DNA)
t=6h: Division → 2N return
Efficiency Metrics
Synchrony Index = (Max cells in phase – Min cells in phase)/(Total cells). Nutrient methods yield 85-95% synchrony vs 20-30% random culture. Duration limited to 3-4 doublings before desynchronization.
Bioprocess Applications
Growth Kinetics: μ = (ln X₂ – ln X₁)/(t₂ – t₁) measured phase-specifically vs mixed culture averaging.
Recombinant Protein: S-phase synchronization maximizes plasmid replication before induction.
Metabolic Engineering: Cell cycle phase-specific enzyme activity profiling (G1: glycolysis high; M-phase: stress response).
GATE Biotechnology Integration
Q.42 connects Q.35-41 sequence: synchronous culture → IPTG induction timing → PPI pathway analysis → Shine-Dalgarno expression → allosteric regulation → metabolic localization. Critical for bioreactor DO control, specific growth rate optimization (μₛ = Yₓₛ·μ).
