101. Which method is best described as shooting DNA-coated gold or tungsten microparticles into target cells?
ⓐ. Transformation
ⓑ. Ligation
ⓒ. Micro-injection
ⓓ. Biolistics
Correct Answer: Biolistics
Explanation: Biolistics, also called the gene gun method, uses tiny metal particles coated with DNA. These microparticles are shot into cells so that the DNA can enter them. The method is especially useful in plant cells, where the cell wall can make other delivery methods difficult. Its defining feature is physical bombardment with DNA-coated particles.
102. Which term is commonly used for the biolistics method of DNA transfer?
ⓐ. Heat-shock cloning
ⓑ. Gene gun
ⓒ. Molecular sieving
ⓓ. Colony blotting
Correct Answer: Gene gun
Explanation: The biolistics technique is popularly called the gene gun method because DNA-coated particles are physically propelled into cells. The name reflects the delivery mechanism rather than the nature of the DNA itself. It is used when direct particle-mediated transfer is useful. The method is especially associated with transformation of plant tissues.
103. A scientist wants to introduce recombinant DNA into plant cells that are difficult to transform by ordinary uptake methods. Which approach is most suitable?
ⓐ. Biolistics using DNA-coated microparticles
ⓑ. Heat shock after calcium treatment
ⓒ. Direct ligation inside the cytoplasm
ⓓ. Agarose gel electrophoresis
Correct Answer: Biolistics using DNA-coated microparticles
Explanation: Plant cells often present an extra barrier because of their cell wall. Biolistics helps overcome this by physically delivering DNA into the cells using coated microparticles. That makes it especially useful for plant transformation. The other methods listed are either better suited to bacteria or are not DNA-delivery methods at all.
104. Which method is correctly matched with its typical application?
ⓐ. Elution — direct DNA transfer into animal nucleus
ⓑ. Micro-injection — direct DNA transfer into animal nucleus
ⓒ. Heat shock — visualization of DNA bands
ⓓ. Ethidium bromide staining — insertion of DNA into plant cells
Correct Answer: Micro-injection — direct DNA transfer into animal nucleus
Explanation: Micro-injection is a direct physical method in which DNA is introduced into the nucleus of an animal cell. The other options mix unrelated techniques with incorrect functions. Elution is used to recover DNA from a gel, while heat shock helps bacterial transformation. Ethidium bromide is used for visualization, not gene transfer.
105. After recombinant DNA is introduced into bacteria, only some cells grow on an ampicillin-containing medium. These growing cells are most likely
ⓐ. non-transformants lacking plasmids
ⓑ. transformants carrying the recombinant DNA
ⓒ. cells with degraded chromosomal DNA
ⓓ. cells that failed to take up any foreign DNA
Correct Answer: transformants carrying the recombinant DNA
Explanation: Growth on antibiotic medium usually indicates that the cells have taken up DNA carrying the relevant resistance marker. Those cells are called transformants. Non-transformants fail to survive because they lack the selectable marker. Antibiotic selection therefore helps separate successful DNA recipients from the rest of the population.
106. Consider the following assertion and reason:
Assertion (A): Disarmed pathogen-based vectors can be used to deliver desired genes into host cells.
Reason (R): Their disease-causing ability is removed, while their natural DNA-delivery ability is retained for biotechnology use.
ⓐ. Both A and R are true, but R is not the correct explanation of A.
ⓑ. A is true, but R is false.
ⓒ. A is false, but R is true.
ⓓ. Both A and R are true, and R is the correct explanation of A.
Correct Answer: Both A and R are true, and R is the correct explanation of A.
Explanation: Some biological agents naturally transfer genetic material into host cells, and that ability can be adapted for biotechnology. When such vectors are disarmed, harmful effects are removed but delivery capacity is preserved. This makes them useful carriers for desired genes. The reason directly explains why pathogen-based systems can be converted into safe gene-transfer tools.
107. Which sequence correctly represents the major steps of recombinant DNA technology from beginning to end?
ⓐ. Transfer into host → ligation → DNA isolation → product extraction
ⓑ. DNA isolation → restriction digestion → isolation of desired fragment → ligation into vector → transfer into host → large-scale culturing → product extraction
ⓒ. Product extraction → host transfer → ligation → DNA isolation
ⓓ. DNA isolation → product extraction → ligation → host transfer
Correct Answer: DNA isolation → restriction digestion → isolation of desired fragment → ligation into vector → transfer into host → large-scale culturing → product extraction
Explanation: Recombinant DNA technology follows a logical order in which the genetic material is first obtained and then manipulated. After the desired fragment is isolated, it is joined to a vector and introduced into a host. The transformed host is then grown to produce the required product in useful quantity. Product recovery comes only after successful culturing and expression.
108. Why is isolation of DNA considered an essential early step in recombinant DNA technology?
ⓐ. Because DNA bands can be seen directly without purification
ⓑ. Because host cells can multiply foreign DNA before it is obtained
ⓒ. Because proteins must be cloned before genes are identified
ⓓ. Because the gene of interest must be separated from the rest of the cellular material before manipulation
Correct Answer: Because the gene of interest must be separated from the rest of the cellular material before manipulation
Explanation: DNA inside a cell is mixed with membranes, proteins, RNA, and many other biomolecules. To work with a selected gene, the genetic material must first be isolated in a usable form. Only then can it be cut, amplified, ligated, or transferred into a host. Isolation therefore creates the starting material for every later recombinant step.
109. Which enzyme is commonly used to break open bacterial cells during isolation of DNA?
ⓐ. Lysozyme
ⓑ. Cellulase
ⓒ. Chitinase
ⓓ. Protease
Correct Answer: Lysozyme
Explanation: Bacterial cells possess a cell wall made largely of peptidoglycan, and lysozyme helps break this barrier. Once the wall is weakened, cellular contents including DNA can be released more easily. This makes lysozyme useful in the early stage of DNA isolation from bacteria. The enzyme is chosen according to the structure of the cell covering being removed.
110. During isolation of DNA from plant cells, which enzyme is especially useful for breaking the cell wall?
ⓐ. Lysozyme
ⓑ. Ribonuclease
ⓒ. Cellulase
ⓓ. Protease
Correct Answer: Cellulase
Explanation: Plant cell walls contain cellulose as a major structural component. Cellulase breaks down this material and helps release the cellular contents. This makes the enzyme particularly suitable when DNA is to be isolated from plant tissues. The treatment is directed at the wall, not at the DNA itself.
111. Which enzyme is most suitable for helping isolate DNA from fungal cells?
ⓐ. Cellulase
ⓑ. Chitinase
ⓒ. Lysozyme
ⓓ. DNA ligase
Correct Answer: Chitinase
Explanation: Fungal cell walls contain chitin, so an enzyme that digests chitin is useful during DNA isolation from fungi. Chitinase helps disrupt the wall and release the contents of the cell. Different organisms require different wall-degrading enzymes because their outer coverings are not chemically identical. Matching the enzyme to the wall material is therefore important.
112. During purification of DNA, which pair of enzymes is used to remove RNA and proteins respectively?
ⓐ. Protease and cellulase
ⓑ. Lysozyme and chitinase
ⓒ. DNA ligase and polymerase
ⓓ. Ribonuclease and protease
Correct Answer: Ribonuclease and protease
Explanation: Purified DNA preparations should be freed from other major biomolecules that may interfere with later steps. Ribonuclease degrades RNA, while protease digests contaminating proteins. Using these enzymes helps obtain cleaner DNA for restriction digestion, ligation, or amplification. The enzymes act on impurities rather than on the DNA target itself.
113. After removal of major contaminants, DNA is commonly precipitated from solution by using
ⓐ. chilled ethanol
ⓑ. warm glycerol
ⓒ. methylene blue
ⓓ. calcium chloride
Correct Answer: chilled ethanol
Explanation: DNA becomes visible as fine threads when precipitated from solution with chilled ethanol. This step helps collect the purified nucleic acid after other cellular components have been removed. The thread-like appearance is a familiar sign of successful DNA precipitation. It is a recovery step, not a cutting or amplifying step.
114. A student isolates DNA and notices thin thread-like material appearing after addition of ice-cold ethanol. This material is most likely
ⓐ. denatured protein
ⓑ. cell wall fragments
ⓒ. precipitated DNA
ⓓ. digested RNA
Correct Answer: precipitated DNA
Explanation: When purified DNA is treated with chilled ethanol, it separates out of the solution as fine threads that can often be spooled out. This visible material is the precipitated DNA itself. The step is widely used during DNA isolation to recover the nucleic acid in a concentrated form. Its thread-like appearance is due to the long polymeric nature of DNA molecules.
115. Why must cells be opened during the initial isolation of genetic material?
ⓐ. Because DNA is enclosed within cellular membranes and cannot be accessed directly
ⓑ. Because DNA must first be converted into protein before purification
ⓒ. Because restriction enzymes can act only on broken chromosomes
ⓓ. Because isolated DNA is produced only outside living cells
Correct Answer: Because DNA is enclosed within cellular membranes and cannot be accessed directly
Explanation: Genetic material is located inside cells and is surrounded by cellular barriers. To obtain DNA, these membranes and other enclosing structures must first be disrupted. Only then can the DNA be released into solution for purification. Cell opening is therefore a necessary starting step in DNA isolation.
116. Which statement correctly explains why different organisms may require different enzymes during DNA isolation?
ⓐ. DNA composition differs completely in bacteria, plants, and fungi.
ⓑ. Their cell coverings differ in composition, so different wall-degrading enzymes are needed.
ⓒ. Restriction enzymes cannot function unless the wall is made of cellulose.
ⓓ. RNA is present only in plant cells and not in bacterial or fungal cells.
Correct Answer: Their cell coverings differ in composition, so different wall-degrading enzymes are needed.
Explanation: Bacteria, plants, and fungi do not have identical outer structures. Bacterial walls are targeted by lysozyme, plant cell walls by cellulase, and fungal walls by chitinase. The reason for this difference is the different chemical makeup of their cell coverings. Matching the enzyme to the wall material helps release DNA efficiently.
117. During the cutting stage of recombinant DNA technology, purified DNA is incubated with a restriction enzyme mainly to
ⓐ. stain the DNA fragments for ultraviolet detection
ⓑ. copy the DNA segment many times in vitro
ⓒ. cleave DNA at specific recognition sites
ⓓ. protect the DNA from ligase activity
Correct Answer: cleave DNA at specific recognition sites
Explanation: Restriction enzymes are used at this stage because they cut DNA in a precise and reproducible manner. The enzyme recognizes a particular nucleotide sequence and breaks the DNA backbone at or near that site. This generates fragments that can later be isolated and joined to a vector. Controlled cleavage is essential for selective gene manipulation.
118. Why is the same restriction enzyme generally used for cutting both the source DNA and the vector DNA?
ⓐ. It prevents the host cell from degrading the recombinant molecule.
ⓑ. It creates compatible ends that can join during ligation.
ⓒ. It increases the copy number of the vector automatically.
ⓓ. It removes selectable markers from the plasmid.
Correct Answer: It creates compatible ends that can join during ligation.
Explanation: When both donor DNA and vector DNA are cut with the same restriction enzyme, they usually produce matching ends. These compatible ends can pair with each other, which makes ligation much easier. The strategy improves the chance of forming a stable recombinant molecule. Compatibility of ends is the key purpose of using the same enzyme.
119. Which method is commonly used to check whether DNA digestion by a restriction enzyme has occurred properly?
ⓐ. Heat-shock treatment
ⓑ. Downstream processing
ⓒ. Agarose gel electrophoresis
ⓓ. Calcium ion treatment
Correct Answer: Agarose gel electrophoresis
Explanation: After restriction digestion, the resulting DNA fragments can be separated and examined on an agarose gel. This helps confirm whether the DNA has been cut and gives an idea of the fragment pattern produced. The method is therefore useful for monitoring the success of digestion. It is an analysis step rather than a transformation or production step.
120. After a desired gene fragment has been isolated and the vector has been cut with the same restriction enzyme, the next essential step is to
ⓐ. expose both to ultraviolet light for replication
ⓑ. transfer both directly into an animal cell nucleus
ⓒ. precipitate both with chilled ethanol again
ⓓ. mix them with DNA ligase to form recombinant DNA
Correct Answer: mix them with DNA ligase to form recombinant DNA
Explanation: Once the insert and vector have compatible ends, they need to be joined into one stable DNA molecule. DNA ligase performs this by sealing the sugar-phosphate backbone between the aligned fragments. Without this step, the donor fragment and vector remain separate. Ligation is therefore the step that produces recombinant DNA itself.
