Question 1

What is gene cloning in biotechnology?

Accepted Answer

Gene cloning is a technique in biotechnology that allows the production of multiple identical copies of a specific gene or DNA fragment. For example, cloning a gene to produce insulin protein for therapeutic use. — Gene cloning is the process of isolating a gene of interest and producing numerous identical copies by inserting it into a vector and replicating it within a host cell. This technique is fundamental for studying genes and producing proteins.

Question 2

Which of the following is NOT a common vector used in gene cloning?

Accepted Answer

Ribosome — Plasmids, bacteriophages, and cosmids are common vectors used to carry foreign DNA into host cells. Ribosomes are cellular organelles involved in protein synthesis, not vectors for gene cloning.

Question 3

What role do restriction enzymes play in gene cloning?

Accepted Answer

Restriction enzymes act as molecular scissors that cut DNA at specific recognition sequences. For example, EcoRI cuts DNA at GAATTC sites producing sticky ends for gene insertion. — Restriction enzymes recognize specific DNA sequences and cut the DNA, creating fragments with sticky or blunt ends. These cuts allow insertion of the gene of interest into vectors for cloning.

Question 4

DNA ligase is essential in gene cloning because it:

Accepted Answer

Joins DNA fragments by forming phosphodiester bonds — DNA ligase joins DNA fragments by catalyzing the formation of phosphodiester bonds between adjacent nucleotides, enabling insertion of the gene into the vector to form recombinant DNA.

Question 5

Which host organism is most commonly used for gene cloning and why?

Accepted Answer

Escherichia coli is the most commonly used host organism because it grows rapidly, is easy to manipulate genetically, and has well-understood molecular biology. For example, E. coli is used to replicate recombinant plasmids containing cloned genes. — E. coli provides the cellular machinery to replicate recombinant DNA efficiently. Its rapid growth and ease of culture make it ideal for gene cloning experiments.

Question 6

Arrange the following steps of gene cloning in the correct order:
1) Transformation
2) Isolation of gene of interest
3) Ligation of gene into vector
4) Selection and screening
5) Cutting vector DNA with restriction enzymes

Accepted Answer

— The correct order is:
2) Isolation of gene of interest
5) Cutting vector DNA with restriction enzymes
3) Ligation of gene into vector
1) Transformation
4) Selection and screening
This sequence ensures successful cloning and identification of recombinant cells.

Question 7

During gene cloning, why must the same restriction enzyme be used to cut both the gene of interest and the vector DNA?

Accepted Answer

Using the same restriction enzyme ensures that the gene fragment and vector have compatible sticky ends, allowing them to join precisely during ligation. For example, EcoRI produces complementary sticky ends on both DNA pieces for efficient insertion. — Compatible sticky ends created by the same restriction enzyme facilitate the joining of gene and vector DNA by DNA ligase, increasing cloning efficiency.

Question 8

What is blue-white screening and how does it help in identifying recombinant clones?

Accepted Answer

Blue-white screening is a technique where insertion of a gene disrupts the lacZ gene in the vector. Recombinant clones form white colonies on X-gal containing media, while non-recombinant clones form blue colonies. For example, white colonies indicate successful insertion of the gene. — The lacZ gene encodes β-galactosidase which cleaves X-gal to produce blue color. Disruption of lacZ by gene insertion prevents blue color formation, allowing easy identification of recombinant clones.

Question 9

Explain the process of transformation in gene cloning.

Accepted Answer

Transformation is the process of introducing recombinant DNA into a host cell, typically bacteria like E. coli. For example, chemically treated E. coli cells take up plasmid DNA containing the gene of interest during transformation. — Transformation allows the uptake of foreign recombinant DNA by host cells, enabling replication and expression of the cloned gene within the host.

Question 10

Why is antibiotic selection used after transformation in gene cloning?

Accepted Answer

Antibiotic selection is used to grow only those host cells that have taken up the vector containing an antibiotic resistance gene. For example, bacteria transformed with plasmids carrying ampicillin resistance survive on ampicillin-containing media. — This selection process ensures that only transformed cells grow, facilitating identification of cells containing recombinant DNA.

Question 11

Which enzyme is used to synthesize DNA from RNA in gene cloning applications?

Accepted Answer

Reverse transcriptase — Reverse transcriptase synthesizes complementary DNA (cDNA) from an RNA template, which is useful for cloning genes expressed as mRNA.

Question 12

How does the use of plasmids as vectors benefit gene cloning?

Accepted Answer

Plasmids are small, circular DNA molecules that replicate independently in bacteria. For example, plasmids carry antibiotic resistance genes and multiple cloning sites, making them ideal vectors for gene insertion and selection. — Their autonomous replication and selectable markers allow easy propagation and identification of recombinant DNA in host cells.

Question 13

What is the significance of sticky ends produced by restriction enzymes in gene cloning?

Accepted Answer

Sticky ends are single-stranded overhangs produced by restriction enzymes that facilitate the base pairing between vector and gene fragments. For example, EcoRI produces sticky ends that allow complementary binding and efficient ligation. — Sticky ends increase the efficiency and specificity of joining DNA fragments during ligation by complementary base pairing.

Question 14

Explain how colony hybridization is used to screen recombinant clones.

Accepted Answer

Colony hybridization uses a labeled DNA probe complementary to the gene of interest to identify recombinant colonies on a plate. For example, colonies hybridizing with the probe contain the inserted gene and can be selected for further study. — This technique allows detection of specific DNA sequences within bacterial colonies, distinguishing recombinant clones from non-recombinant ones.

Question 15

A gene of interest is 1500 base pairs long. After digestion with a restriction enzyme, it produces sticky ends. The vector plasmid is 3000 base pairs. After ligation and transformation into E. coli, how would you confirm that the recombinant plasmid contains the gene insert?

Accepted Answer

Confirmation can be done by restriction digestion of isolated plasmid DNA followed by gel electrophoresis to observe fragments of 1500 bp and 3000 bp. Alternatively, blue-white screening or PCR can be used to verify the presence of the insert. — Restriction digestion releases the insert, allowing size comparison. Blue-white screening differentiates recombinant colonies by color. PCR amplification with gene-specific primers confirms the insert.

Gene Cloning

Gene Cloning — Study Notes

Introduction

Tools for Gene Cloning

Process of Gene Cloning

Practice Questions — Gene Cloning

All 13 Chapters in Biotechnology