201. Two transformed bacterial populations carry the same foreign DNA insert:
| Population | Transformed cells | Vector copies per cell |
|---|
| P | \(300\) | \(2\) |
| Q | \(40\) | \(50\) |
Assuming one insert per vector molecule, which population contains more plasmid-linked copies of the target DNA?
ⓐ. Q, with approximately \(2{,}000\) copies compared with \(600\) in P
ⓑ. P, because it contains more transformed cells regardless of vector copy number
ⓒ. Both contain exactly \(600\) copies
ⓓ. Both contain exactly \(2{,}000\) copies
Correct Answer: Q, with approximately \(2{,}000\) copies compared with \(600\) in P
Explanation: The number of linked target-DNA copies depends on both the number of transformed cells and the vector copy number within each cell. Population P contains approximately \(300 \times 2 = 600\) recombinant vector copies. Population Q contains approximately \(40 \times 50 = 2{,}000\) copies. Even though Q has fewer transformed cells, its much higher vector copy number produces a greater total number of plasmid-linked target sequences under the supplied assumptions. This is a useful example of why biological interpretation should not rely on a single variable such as cell number when vector replication also contributes directly to DNA yield.
202. In a pBR322 experiment, transformed colonies are first grown on an ampicillin master plate. Replica plating onto tetracycline gives the following result:
| Colony position | Ampicillin master plate | Tetracycline replica plate |
|---|
| P | Growth | No growth |
| Q | Growth | Growth |
| R | Growth | Growth |
Foreign DNA was inserted at the BamHI site within tetR. Which colony should be recovered from the master plate as the strongest recombinant candidate?
ⓐ. Q
ⓑ. P
ⓒ. R
ⓓ. Q and R only
Correct Answer: P
Explanation: All three colonies grew on ampicillin, showing that they carry plasmid DNA with functional ampR. The distinguishing information comes from the tetracycline replica plate. Insertion of foreign DNA at the BamHI site within tetR causes insertional inactivation, so a recombinant is expected to be ampicillin-resistant but tetracycline-sensitive. Colony P displays this pattern because it grows on the master ampicillin plate but fails to grow at the corresponding position on tetracycline. The original master plate is important because the tetracycline-sensitive recombinant cannot be recovered from a plate on which it failed to grow; its corresponding colony must be selected from the preserved ampicillin plate.
203. A student makes the claim: "If a colony survives ampicillin after pBR322 transformation, the foreign DNA insert must be present." Which evaluation is most accurate?
ⓐ. Correct, because ampicillin resistance specifically proves that foreign DNA has been inserted into pBR322.
ⓑ. Correct, because any cell that acquires pBR322 by transformation necessarily carries the desired foreign insert.
ⓒ. Correct only if the same colony also retains tetracycline resistance, which confirms the desired insertion.
ⓓ. Incorrect, because ampicillin survival shows pBR322 uptake but does not prove that the plasmid carries an insert.
Correct Answer: Incorrect, because ampicillin survival shows pBR322 uptake but does not prove that the plasmid carries an insert.
Explanation: In the stated BamHI insertion scheme, the foreign DNA is inserted within tetR while ampR remains functional. Both recombinant and non-recombinant pBR322 molecules can therefore allow their host cells to survive on ampicillin. Ampicillin selection establishes which cells acquired plasmid DNA, but it does not establish which plasmids actually contain the foreign insert. Tetracycline testing is required to distinguish the ampR tetS recombinant pattern from ampR tetR non-recombinant transformants. The claim therefore confuses selection of transformants with screening for recombinants.
204. A DNA-isolation protocol for fungal material uses lysozyme for wall disruption, omits ribonuclease, includes protease, and finally adds chilled ethanol. Which combination of consequences is most reasonable?
ⓐ. Wall disruption is appropriate for fungi, and omission of ribonuclease still removes RNA completely.
ⓑ. Wall disruption is appropriate, and chilled ethanol selectively removes all RNA while leaving DNA soluble.
ⓒ. Wall disruption is mismatched and RNA may remain, although protein removal and DNA precipitation are included.
ⓓ. Wall disruption and RNA removal are both correct because the listed enzymes are functionally interchangeable.
Correct Answer: Wall disruption is mismatched and RNA may remain, although protein removal and DNA precipitation are included.
Explanation: Fungal material is associated with chitin-containing walls, so chitinase is the appropriate source-specific lytic enzyme rather than lysozyme, which is used for bacterial cells. Omitting ribonuclease means that RNA released during cell disruption may remain as a contaminant. Protease can still remove proteins, and chilled ethanol can precipitate the purified DNA as visible threads. The protocol therefore contains both correct and incorrect elements. Hard troubleshooting requires identifying which experimental problem each reagent solves instead of treating all purification enzymes as interchangeable.
205. Purified source DNA and vector DNA are incubated with the correct restriction enzyme, but the reaction conditions are unsuitable for enzyme activity. Gel analysis afterward shows essentially no expected cleavage products. If the laboratory proceeds directly to the planned ligation step, what is the most likely root cause of poor recombinant formation?
ⓐ. DNA ligase converted the uncleaved source and vector DNA into RNA before ligation.
ⓑ. Restriction cleavage failed, so compatible insert and vector ends were not generated.
ⓒ. Agarose electrophoresis destroyed the enzyme recognition sites in both source and vector DNA.
ⓓ. The selectable marker blocked restriction cleavage of both source and vector DNA.
Correct Answer: Restriction cleavage failed, so compatible insert and vector ends were not generated.
Explanation: Recombinant construction depends on successful preparation of both the source fragment and the vector. If the restriction enzyme is present but the reaction conditions do not support its activity, the DNA may remain largely uncut. Gel electrophoresis can reveal this failure before ligation is attempted. DNA ligase cannot compensate for missing restriction cleavage because it joins DNA ends that have already been appropriately generated and aligned. The root problem therefore lies upstream of ligation: the molecular substrates needed for recombinant assembly were never properly produced.
206. A restriction digest of source DNA produces several fragments, including the desired gene-containing fragment. Instead of isolating the required band, all fragments are mixed directly with an opened vector and DNA ligase. Why does this reduce control over recombinant construction?
ⓐ. Gel purification is required because elution creates the vector origin needed for subsequent plasmid replication.
ⓑ. DNA ligase preferentially joins RNA fragments, so all restriction-generated DNA fragments are excluded from ligation.
ⓒ. Restriction digestion destroys gene function in every DNA fragment, making selective recovery unnecessary.
ⓓ. Several source fragments can compete for vector ligation, so the desired insert is not selectively enriched.
Correct Answer: Several source fragments can compete for vector ligation, so the desired insert is not selectively enriched.
Explanation: Restriction digestion often produces a mixture of DNA fragments. Only one of those fragments may contain the desired gene. Electrophoretic separation followed by recovery of the appropriate band allows the researcher to enrich specifically for the intended insert before ligation. If the entire digest is combined with the opened vector, unwanted fragments may also possess compatible ends and can participate in ligation. The problem is therefore not that ligase is defective but that the experimental mixture lacks insert specificity. Fragment isolation is an important control step between restriction digestion and recombinant assembly.
207. Four PCR tubes contain the same template DNA:
| Tube | Two primers | Nucleotides | Thermostable polymerase |
|---|
| P | Present | Present | Present |
| Q | Absent | Present | Present |
| R | Present | Absent | Present |
| S | Present | Present | Absent |
Assuming all other conditions are appropriate, which tube has the complete core machinery for repeated amplification of the defined target?
ⓐ. Q
ⓑ. R
ⓒ. S
ⓓ. P
Correct Answer: P
Explanation: Tube P contains the template, both primers, free nucleotides and thermostable DNA polymerase, providing the essential components required for repeated PCR cycling. Tube Q lacks primers, so the target boundaries and starting points for DNA synthesis are missing. Tube R lacks the nucleotide building blocks required to construct new strands. Tube S lacks the polymerase that catalyses primer extension. The comparison demonstrates that PCR is a coordinated system: each component performs a distinct role, and the presence of the template alone cannot compensate for the absence of primers, substrates or enzyme.
208. In a PCR experiment, a new primer pair is designed so that the primers anneal to valid complementary regions farther apart on the same template than the original pair. If amplification proceeds successfully, what is the most reasonable prediction?
ⓐ. The PCR must amplify exactly the same segment because primer position never affects target definition.
ⓑ. The boundaries of the amplified DNA segment will change according to the new primer-binding positions.
ⓒ. The template automatically becomes a plasmid.
ⓓ. Only the number of nucleotides in the reaction changes, not the identity of the amplified region.
Correct Answer: The boundaries of the amplified DNA segment will change according to the new primer-binding positions.
Explanation: PCR specificity is determined largely by where the two primers anneal on the template DNA. The primers provide the starting points from which DNA polymerase extends, so the region lying between the selected primer-binding positions becomes the principal amplified target. Moving the primers to different valid flanking positions therefore changes the boundaries of the DNA segment that is copied. This is a deeper consequence of primer specificity: primers do not merely enable amplification; they help define which part of a complex DNA template is selectively enriched.
209. A PCR machine is programmed so that each cycle performs denaturation followed immediately by extension, with no primer-annealing stage. All reagents are otherwise correct. Which outcome is most likely?
ⓐ. Amplification improves because denatured DNA can be copied without primer annealing.
ⓑ. DNA ligase substitutes for primer binding and provides the starting point for extension.
ⓒ. Target amplification is impaired because polymerase lacks annealed primers for extension.
ⓓ. The reaction becomes equivalent to bacterial cloning because annealing is omitted.
Correct Answer: Target amplification is impaired because polymerase lacks annealed primers for extension.
Explanation: Denaturation separates the template strands, but this alone does not provide DNA polymerase with a correctly positioned starting point. During annealing, the primers bind to complementary target sequences and establish the sites from which new DNA synthesis begins. If the reaction moves directly from strand separation to extension without allowing primer binding, efficient target-specific DNA synthesis cannot proceed as intended. PCR stages are therefore ordered because each creates the molecular condition needed for the next: denaturation exposes the template, annealing positions the primers and extension builds new DNA.
210. A target DNA segment is first amplified extensively by PCR, then ligated into a plasmid with a functional ori, and finally introduced into bacterial cells. Which statement best describes the two amplification phases?
ⓐ. PCR multiplies target DNA in vitro, whereas vector replication multiplies the linked target inside host cells.
ⓑ. Both phases use the same mechanism because PCR requires a plasmid to replicate inside bacterial host cells.
ⓒ. Only the host-vector phase increases DNA copy number because PCR merely changes the physical appearance of DNA.
ⓓ. The host-vector phase replaces ligation because PCR-amplified DNA inserts itself into a plasmid automatically.
Correct Answer: PCR multiplies target DNA in vitro, whereas vector replication multiplies the linked target inside host cells.
Explanation: PCR and cloning can both increase the amount of a selected DNA sequence, but they do so by fundamentally different mechanisms. PCR is a cell-free amplification reaction driven by template DNA, primers, nucleotides and polymerase. After the amplified fragment is ligated into a vector carrying an appropriate ori and transferred into a host, replication of the recombinant vector can further multiply the inserted sequence inside living cells. The two stages are therefore complementary rather than redundant. PCR provides rapid in vitro enrichment, whereas vector-based cloning provides biological maintenance and propagation.
211. A continuous-culture record shows that cells remain in a highly active growth state while fresh medium is supplied and spent medium is removed. When fresh-medium supply is progressively reduced, active growth and product output both decline. Which interpretation is best supported by continuous-culture physiology?
ⓐ. Product output falls because recombinant DNA is converted into agarose when nutrients decline.
ⓑ. Medium flow changes only colony colour and does not affect cell physiology or product formation.
ⓒ. Reduced fresh-medium supply directly removes the vector ori from recombinant cells.
ⓓ. Favourable nutrient supply helps sustain active growth, biomass and recombinant-product formation.
Correct Answer: Favourable nutrient supply helps sustain active growth, biomass and recombinant-product formation.
Explanation: Continuous culture is designed to maintain a physiologically active population by supplying fresh nutrients while removing spent medium. When nutrient replacement becomes inadequate, cells are less able to remain in the active log or exponential phase associated with strong biomass accumulation and productive metabolism. The observed fall in product output therefore reflects changing culture physiology rather than loss of recombinant DNA itself. This connects culture management with biotechnology yield: the engineered genetic system provides the capacity to make the product, while the growth environment influences how effectively that capacity is realised.
212. Two stirred-tank bioreactors contain the same recombinant cells and nutrients:
| Reactor | Mechanical stirring | Sterile-air sparging | Observed oxygen availability |
|---|
| P | Present | Absent | Lower |
| Q | Present | Present | Higher |
Which explanation best accounts for the difference?
ⓐ. Sparging destroys oxygen and forces cells to use less.
ⓑ. Mechanical stirring prevents oxygen transfer whenever air is bubbled.
ⓒ. Air bubbles in Q increase the gas-liquid interface and can improve oxygen transfer to the culture.
ⓓ. Q must contain a different recombinant gene because oxygen availability cannot depend on reactor design.
Correct Answer: Air bubbles in Q increase the gas-liquid interface and can improve oxygen transfer to the culture.
Explanation: A sparged stirred-tank reactor combines mechanical mixing with bubbling of sterile air through the culture. The bubbles create additional gas-liquid contact area, allowing oxygen to move more effectively into the liquid phase. Stirring then helps distribute oxygen and other culture components. Because the two reactors are otherwise stated to contain the same cells and nutrients, the additional sparging in Q provides the most direct explanation for its greater oxygen availability. Reactor design therefore influences process performance through physical control of the cellular environment rather than by altering the recombinant gene itself.
213. A sparged bioreactor continues receiving sterile air, but the agitator fails. Which consequence is most reasonable?
ⓐ. Mixing becomes poorer, so cells, nutrients and oxygen may become less uniformly distributed.
ⓑ. Mixing remains fully uniform because sterile-air bubbles replace all mechanical agitation.
ⓒ. Agitator failure immediately removes the recombinant plasmid from every production cell.
ⓓ. Foam control automatically performs all mixing and oxygen-distribution functions.
Correct Answer: Mixing becomes poorer, so cells, nutrients and oxygen may become less uniformly distributed.
Explanation: Aeration and agitation perform related but distinct functions. Sparging introduces air and improves the gas-liquid interface, whereas the agitator mixes the culture contents and helps distribute cells, nutrients and dissolved gases throughout the vessel. Continued air supply therefore does not make mechanical mixing irrelevant. If agitation fails, local differences in nutrient and oxygen availability can develop even though bubbles are still entering the reactor. Bioreactor efficiency depends on coordinated control systems, and failure of one component can reduce overall process uniformity without altering the recombinant DNA itself.
214. A production vessel begins developing heavy foam while pH, temperature and oxygen readings remain within their intended ranges. Which response most directly addresses the observed process problem?
ⓐ. Adjust the foam-control system while continuing to monitor the remaining culture variables.
ⓑ. Add a restriction endonuclease to digest the foam without changing culture conditions.
ⓒ. Remove the vector ori from the production cells to prevent further foam formation.
ⓓ. Stop all sampling because sampling ports are the direct cause of foam accumulation.
Correct Answer: Adjust the foam-control system while continuing to monitor the remaining culture variables.
Explanation: Foam formation is a physical process problem that can arise during aeration and agitation of large-scale cultures. Bioreactors therefore include dedicated foam-control mechanisms. Because the stated pH, temperature and oxygen values remain appropriate, there is no evidence that those control systems are the primary cause of the immediate problem. The correct response is to address foam directly while continuing normal monitoring of the culture. This type of process diagnosis requires matching an observed production problem to the bioreactor subsystem designed to control it rather than changing unrelated molecular biology steps.
215. Samples taken through a bioreactor sampling port show that product concentration rises normally for several hours and then falls at the same time that culture pH moves outside its target range. Oxygen and temperature remain stable. Which conclusion is best supported?
ⓐ. The sampling port caused a mutation in the recombinant gene during withdrawal.
ⓑ. Oxygen supply must have failed because every productivity change reflects aeration.
ⓒ. Loss of pH control best explains the decline while oxygen and temperature remained stable.
ⓓ. The decrease proves that DNA ligation failed before the production culture was established.
Correct Answer: Loss of pH control best explains the decline while oxygen and temperature remained stable.
Explanation: The sampling system provides time-dependent information about the culture, allowing changes in product formation to be compared with changes in controlled variables. Here, the decline in product coincides with pH leaving its target range, while oxygen and temperature remain stable. This makes pH control the most directly implicated process variable. The recombinant construct must already have been successfully established because production occurred normally at first. The problem therefore lies in maintaining an appropriate physiological environment during scale-up rather than in the earlier DNA-construction stage.
216. A purified recombinant therapeutic protein has been formulated for administration, but no appropriate clinical evaluation has yet been performed. Which statement is most accurate?
ⓐ. Purification alone establishes clinical suitability, so the therapeutic is ready for use.
ⓑ. Any product made in a bioreactor can be used without clinical evaluation.
ⓒ. Additional plasmid replication is the only remaining requirement before therapeutic use.
ⓓ. A therapeutic formulation still requires appropriate clinical evaluation before use.
Correct Answer: A therapeutic formulation still requires appropriate clinical evaluation before use.
Explanation: Production and purification establish that the biotechnology product can be manufactured and isolated, while formulation prepares it in a usable form. For a therapeutic drug product, however, appropriate clinical evaluation is an additional requirement before use. The need for such evaluation should not be generalised identically to every biotechnology product, because downstream and regulatory requirements depend on the nature and intended use of the product. The scenario therefore highlights a product-specific downstream requirement rather than another genetic-engineering step.
217. Which comparison between quality control and clinical evaluation is most appropriate?
ⓐ. Both terms refer to antibiotic-based plasmid selection rather than assessment of the final biotechnology product.
ⓑ. Quality control applies to finished products; clinical evaluation is additionally needed for appropriate therapeutics.
ⓒ. Clinical evaluation replaces product purification, whereas quality control replaces recombinant-gene expression.
ⓓ. Neither process is required once large-scale production has produced the desired amount of product.
Correct Answer: Quality control applies to finished products; clinical evaluation is additionally needed for appropriate therapeutics.
Explanation: Quality control is a broad requirement associated with assessing whether a finished biotechnology product meets appropriate standards. Clinical evaluation is more specifically relevant when a formulation is intended for therapeutic use and must be assessed before use as a drug. These processes are therefore related to product readiness but are not identical. A biotechnology process may require separation, purification, formulation and quality assessment, with clinical evaluation added where the product type demands it. This distinction prevents the incorrect assumption that every biotechnology product follows exactly the same post-production pathway.
218. Two purified biotechnology products differ in stability. Product P loses activity during storage unless a suitable preservative is included in its final preparation, whereas product Q remains stable without that same additive. Which downstream principle is most appropriate?
ⓐ. Both products must receive the same preservative because downstream formulation is fixed for all products.
ⓑ. Product stability is determined only by the recombinant vector used during cloning.
ⓒ. Final formulation should be adapted to the properties and intended use of each product.
ⓓ. Purification becomes unnecessary whenever a preservative is added during formulation.
Correct Answer: Final formulation should be adapted to the properties and intended use of each product.
Explanation: Formulation is a downstream step that prepares a purified biotechnology product for storage, handling or use. Because products differ in chemical properties, stability and intended application, their formulations need not be identical. A preservative may be appropriate for one product but unnecessary or unsuitable for another. This product-specific approach does not replace purification or quality control; it follows successful recovery and purification and is designed around the requirements of the final product.
219. A cloning project gives the following results:
| Stage | Observation |
|---|
| P. Recombinant-vector construction | Correct insert confirmed |
| Q. Transformation | Many selectable transformants obtained |
| R. Gene expression | Desired protein detected |
| S. Large-scale culture | High product quantity obtained |
| T. Final preparation | Product remains mixed with major unwanted components |
Where is the strongest remaining failure?
ⓐ. Failure in restriction digestion and recombinant-vector construction
ⓑ. Failure in transformation and selection of plasmid-bearing host cells
ⓒ. Failure in expression of the cloned gene and product synthesis
ⓓ. Failure in downstream recovery and purification of the final product
Correct Answer: Failure in downstream recovery and purification of the final product
Explanation: Each earlier stage has direct evidence of success. The correct insert confirms recombinant construction, selectable colonies demonstrate transformation, protein detection demonstrates expression, and high product quantity shows that scale-up has worked. The remaining defect appears only at the final preparation stage, where unwanted material has not been sufficiently removed. This identifies downstream recovery and purification as the unresolved problem. Locating the failure from the experimental evidence prevents an incorrect return to earlier genetic-engineering stages that have already succeeded.
220. The following sequence is proposed for producing a recombinant protein:
P. PCR amplification of the desired DNA segment
Q. Ligation into a suitable vector
R. Introduction of recombinant DNA into a competent host
S. Expression of the cloned gene
T. Large-scale culture
U. Product recovery and purification
Which ordering is biologically coherent?
ⓐ. \(U\rightarrow T\rightarrow S\rightarrow R\rightarrow Q\rightarrow P\)
ⓑ. \(P\rightarrow R\rightarrow Q\rightarrow S\rightarrow U\rightarrow T\)
ⓒ. \(P\rightarrow Q\rightarrow R\rightarrow S\rightarrow T\rightarrow U\)
ⓓ. \(Q\rightarrow P\rightarrow T\rightarrow R\rightarrow S\rightarrow U\)
Correct Answer: \(P\rightarrow Q\rightarrow R\rightarrow S\rightarrow T\rightarrow U\)
Explanation: PCR can first provide many copies of the target DNA. The amplified segment can then be ligated into an appropriate vector to generate recombinant DNA. That recombinant molecule must enter a suitable host before the cloned gene can be expressed. Once expression has been established, the production system can be expanded to large scale, after which the product is recovered and purified through downstream processing. The order reflects real dependencies between stages: purification cannot precede production, expression cannot precede host introduction, and recombinant-vector construction must occur before the vector can be propagated in the host.
