Explaining Lysine Decrease in Reactor
The question describes a scenario where Lysine concentration is decreasing in a bioreactor containing a threonine auxotroph strain, despite stable operating conditions and no contamination.
Investigating the Cause of Lysine Reduction
The core issue is the declining Lysine levels. Let's analyze the potential causes:
- Threonine Auxotroph Nature: The microorganism requires threonine to grow.
- Decreasing Lysine: This indicates either reduced production or increased degradation/consumption of Lysine.
- Stable Conditions & No Contamination: This rules out external factors like operational errors or unwanted microbes.
Role of Revertants in Lysine Synthesis
The most probable explanation is the growth of revertants.
- Revertants are cells within the culture that have undergone a secondary mutation, regaining the ability to synthesize their own threonine.
- These revertant cells may have lost or altered the metabolic pathways responsible for Lysine overproduction, which is often linked to amino acid biosynthesis regulation.
- Alternatively, revertants might preferentially consume Lysine or degrade it as part of their altered metabolism.
- The growth of these revertants, even if not initially dominant, can lead to a net decrease in the overall Lysine concentration in the reactor over time.
Evaluating Other Options
- Accumulation of ethanol: Ethanol is a fermentation byproduct, typically associated with specific metabolic pathways (e.g., yeast), and not a direct cause for Lysine decrease in this context.
- Production of citric acid: Citric acid is another metabolic product, unrelated to Lysine stability or the auxotrophic nature of the strain described.
- Unutilized phosphoenol pyruvate (PEP): While PEP is crucial for central metabolism, its unutilization doesn't specifically explain Lysine degradation or reduced production in the way revertant growth does.
Therefore, the selective growth advantage or altered metabolic activity of revertant cells is the most likely reason for the observed decrease in Lysine concentration.
Important Questions from Mutations and Mutagenesis
Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].
Assertion [a]: Chromosome mutations can change the structure of chromosomes.
Reason [r]: All chromosome mutations arise due to nondisjunction of chromosomes during mitosis or meiosis.A DNA sequence, 5'-ATGGACGTGCTTCCCAAAGCATCGGGC-3', is mutated to obtain
P. 5'-ATGGACGTGCTTCaCAAAGCATCGGGC-3′
Q. 5′-ATGGACGTGCTTCCCgAAAGCATCGGGC-3′
R. 5'-ATGGACGTGCTTCC-AAAGCATCGGGC-3′
S. 5'-ATGGACGTGCTTCCCAAtGCATCGGGC-3′
T. 5'-ATGGACGaGCTTCCCAAAGCATCGGGC-3′
[Point mutations are shown in the lower case or ‘–' within the sequences]
Which of the above mutant sequences DO NOT have frame-shift?
- A mutation in a gene that codes for a polypeptide results in a variant polypeptide that lacks the last three amino acids. What type of mutation is this?
- A truncated polypeptide is synthesized due to a nonsense mutation. Where would you introduce another mutation to obtain a full-length polypeptide?
Determine the correctness or otherwise of the following Assertion (a) and the Reason (r).
Assertion : N-methyl-N'-nitro-N-nitrosoguanidine (NTG) is an effective chemical mutagen.
Reason: Mutations induced by NTG mainly are the GC $\rightarrow$ AT transitions.
