CBSE Class 12 Biology (2026–27)
Chapter 9: Biotechnology: Principles and Processes
20 Important Questions and Answers
1. What are the two core principles of biotechnology?
Answer:
Modern biotechnology is based on two fundamental principles. The first is genetic engineering, which involves altering the genetic material (DNA or RNA) of an organism and introducing it into another organism to obtain desired traits. The second principle is the maintenance of sterile conditions during industrial processes to ensure the growth of only the desired microorganisms or cells. This helps in the large-scale production of useful products such as vaccines, antibiotics, enzymes, and hormones. These principles have enabled scientists to develop genetically modified organisms and improve agricultural, medical, and industrial products. Together, they form the foundation of modern biotechnology.
2. What is recombinant DNA (rDNA) technology?
Answer:
Recombinant DNA (rDNA) technology is a technique in which DNA from two different sources is combined to form a new DNA molecule. This process involves isolating a desired gene, cutting DNA with restriction enzymes, inserting the gene into a vector, and transferring it into a host organism. The host then expresses the inserted gene and produces the desired product. Recombinant DNA technology has numerous applications in medicine, agriculture, and industry. It is used to produce insulin, vaccines, growth hormones, and genetically modified crops. This technology allows scientists to transfer specific genes without introducing unwanted traits.
3. What are restriction enzymes? Why are they called molecular scissors?
Answer:
Restriction enzymes are special proteins that recognize specific DNA sequences and cut the DNA at those sites. They are naturally found in bacteria and protect them from invading viral DNA. These enzymes cut DNA at particular palindromic sequences, producing sticky or blunt ends. Because they precisely cut DNA molecules into fragments, they are commonly called molecular scissors. Restriction enzymes are essential tools in genetic engineering because they allow scientists to isolate desired genes and create recombinant DNA molecules. EcoRI, HindIII, and BamHI are common examples used in biotechnology laboratories.
4. Explain the naming system of restriction enzymes using EcoRI.
Answer:
Restriction enzymes are named according to the bacterium from which they are isolated. In EcoRI, the letter “E” comes from the genus Escherichia, “co” from the species coli, “R” indicates the bacterial strain RY13, and “I” shows that it was the first enzyme isolated from that strain. EcoRI recognizes the palindromic sequence GAATTC and cuts between G and A, producing sticky ends. This systematic naming helps scientists identify the origin and characteristics of different restriction enzymes. Such enzymes play a crucial role in recombinant DNA technology and gene cloning experiments.
5. What are palindromic nucleotide sequences?
Answer:
A palindromic nucleotide sequence is a DNA sequence that reads the same in the 5’→3′ direction on both complementary strands. For example, the sequence recognized by EcoRI is GAATTC. Restriction enzymes identify these specific palindromic sites and cut the DNA at precise positions. Palindromic sequences are important because they ensure accurate cleavage of DNA during genetic engineering procedures. The sticky ends generated after cutting facilitate the joining of DNA fragments from different sources. Therefore, palindromic sequences play a significant role in recombinant DNA technology and gene cloning.
6. Differentiate between sticky ends and blunt ends.
Answer:
Sticky ends are short single-stranded overhangs produced when restriction enzymes cut DNA in a staggered manner. These overhangs can easily pair with complementary DNA fragments, making ligation efficient. In contrast, blunt ends are produced when DNA is cut straight across both strands without creating overhangs. Blunt-end ligation is generally less efficient because there is no base pairing to guide the joining process. Sticky ends are preferred in recombinant DNA technology because they increase the chances of successful insertion of foreign DNA into vectors. Both types of ends are useful depending on the experimental requirement.
7. What is the role of DNA ligase in biotechnology?
Answer:
DNA ligase is an enzyme that joins DNA fragments by forming phosphodiester bonds between adjacent nucleotides. After restriction enzymes cut DNA and generate fragments, DNA ligase seals the gaps and joins the desired gene with a vector DNA. This process creates recombinant DNA molecules. Without DNA ligase, foreign DNA fragments cannot be permanently attached to vectors. Therefore, it is considered one of the most important enzymes in genetic engineering. DNA ligase ensures the stability of recombinant DNA and enables its replication inside host cells, leading to the production of desired proteins or traits.
8. What is a cloning vector? Mention its important features.
Answer:
A cloning vector is a DNA molecule used to carry foreign DNA into a host cell for replication. Common vectors include plasmids, bacteriophages, BACs, and YACs. An ideal cloning vector must possess an origin of replication (ori), which allows replication inside the host cell. It should also contain selectable marker genes such as antibiotic resistance genes for identifying transformed cells. Additionally, vectors have restriction sites where foreign DNA can be inserted. These features help scientists clone and multiply the desired DNA fragment efficiently. Cloning vectors are essential tools in recombinant DNA technology.
9. What is the significance of the origin of replication (ori)?
Answer:
The origin of replication (ori) is a specific DNA sequence present in cloning vectors where DNA replication begins. It controls the replication of the vector inside the host cell and determines the number of copies produced. A vector with a suitable ori can replicate independently and maintain the inserted foreign gene. The efficiency of gene cloning largely depends on the ori because it influences the yield of recombinant DNA. Therefore, the origin of replication is a crucial feature of cloning vectors and is essential for successful genetic engineering experiments.
10. What are selectable markers?
Answer:
Selectable markers are genes present in cloning vectors that help identify transformed host cells. These genes usually provide resistance to antibiotics such as ampicillin or tetracycline. When bacteria are grown on media containing these antibiotics, only those cells that have taken up the vector survive. Thus, selectable markers help scientists distinguish transformed cells from non-transformed cells. They are extremely useful during recombinant DNA experiments because they simplify the screening process. Without selectable markers, identifying host cells carrying recombinant DNA would be difficult and time-consuming.
11. What is PCR? Mention its importance.
Answer:
Polymerase Chain Reaction (PCR) is a technique used to amplify a specific DNA segment and produce millions to billions of copies in a short time. Developed by Kary Mullis, PCR requires DNA templates, primers, nucleotides, and Taq DNA polymerase. It is widely used in medical diagnosis, forensic science, DNA fingerprinting, genetic research, and biotechnology. PCR enables scientists to obtain large quantities of DNA from a very small sample. This makes it an indispensable tool in modern molecular biology and genetic engineering.
12. Describe the three steps of PCR.
Answer:
PCR consists of three main steps. The first step is denaturation, in which double-stranded DNA is heated to separate the strands. The second step is annealing, where primers bind to complementary sequences on the DNA template. The third step is extension, during which Taq DNA polymerase synthesizes new DNA strands at about 72°C. These three steps are repeated through multiple cycles, leading to exponential amplification of the target DNA sequence. PCR can generate billions of copies of a DNA fragment within a few hours, making it highly efficient.
13. Why is Taq DNA polymerase used in PCR?
Answer:
Taq DNA polymerase is obtained from the bacterium Thermus aquaticus, which lives in hot springs. This enzyme is thermostable and remains active even at high temperatures used during PCR. During the denaturation step, DNA is heated to around 94–98°C. Ordinary DNA polymerases would become inactive at such temperatures, but Taq polymerase survives and continues DNA synthesis during the extension phase. Its heat resistance eliminates the need to add fresh enzyme after every cycle. Therefore, Taq DNA polymerase is an essential component of PCR technology.
14. What is gel electrophoresis?
Answer:
Gel electrophoresis is a laboratory technique used to separate DNA fragments according to their size. DNA samples are loaded into wells of an agarose gel and subjected to an electric field. Since DNA carries a negative charge, it moves toward the positive electrode. Smaller DNA fragments move faster and travel farther than larger fragments. After separation, the DNA bands are visualized using staining methods. Gel electrophoresis helps scientists identify, isolate, and analyze specific DNA fragments required for recombinant DNA technology and genetic studies.
15. What is transformation in recombinant DNA technology?
Answer:
Transformation is the process by which a host cell, usually a bacterium, takes up recombinant DNA from its surroundings. During genetic engineering, recombinant plasmids carrying the desired gene are introduced into competent bacterial cells. Once inside, the plasmid replicates and expresses the inserted gene. Transformation is a crucial step because it allows the recombinant DNA to multiply within living cells. Scientists then select transformed cells using selectable markers. Successful transformation leads to the production of desired proteins and the cloning of specific genes.
16. What is a bioreactor?
Answer:
A bioreactor is a large vessel used for the industrial-scale cultivation of microorganisms, plant cells, or animal cells under controlled conditions. It provides optimum temperature, pH, oxygen supply, nutrients, and agitation for maximum growth and product formation. Bioreactors are widely used in the production of antibiotics, enzymes, vaccines, hormones, and other biotechnological products. They ensure efficient large-scale manufacturing while maintaining sterile conditions. Modern biotechnology industries rely heavily on bioreactors for commercial production of biologically important substances.
17. What is downstream processing?
Answer:
Downstream processing refers to all the steps carried out after the formation of a desired biotechnological product. These steps include separation, purification, quality testing, formulation, and packaging. The objective is to obtain a pure and marketable product. For pharmaceuticals such as vaccines and medicines, additional clinical testing and quality control measures are required. Downstream processing is crucial because impurities can affect the effectiveness and safety of the final product. Thus, it ensures that biotechnological products meet industrial and medical standards before reaching consumers.
18. Explain the role of competent cells in genetic engineering.
Answer:
Competent cells are host cells that have been treated to efficiently take up foreign DNA. Under normal conditions, bacterial cells do not readily absorb recombinant DNA. Therefore, scientists use chemical treatments or electrical pulses to make the cell membrane permeable. These modified cells are called competent cells. They can easily accept plasmids carrying the desired gene during transformation. Competent cells are essential in recombinant DNA technology because they increase the efficiency of gene transfer and help produce large numbers of recombinant organisms for research and industrial applications.
19. What is insertional inactivation?
Answer:
Insertional inactivation is a technique used to identify recombinant cells. In this method, a foreign DNA fragment is inserted into a marker gene present in a cloning vector, disrupting its normal function. For example, insertion of a gene into an antibiotic-resistance gene may cause loss of resistance. Recombinant cells can then be distinguished from non-recombinant cells by observing their growth on selective media. This method simplifies the identification of successful recombinants and is widely used in cloning experiments involving vectors such as pBR322.
20. List the major tools of recombinant DNA technology.
Answer:
The major tools of recombinant DNA technology include restriction enzymes, DNA ligase, cloning vectors, competent host cells, and DNA polymerases. Restriction enzymes cut DNA at specific sites, while DNA ligase joins DNA fragments together. Cloning vectors carry foreign genes into host cells. Competent host cells accept and replicate recombinant DNA. DNA polymerases, especially Taq polymerase, are used in DNA amplification through PCR. These tools work together to isolate, clone, amplify, and express desired genes. They form the backbone of modern biotechnology and genetic engineering applications.