Recombinant DNA

Q1: Bacterial cells protect their own DNA from degradation by restriction endonucleases by

A methylating the DNA at the sites that the enzyme recognizes

B deleting all recognition sites from the genome

C not producing any restriction endonucleases

D having anti restriction endonucleases

ANS:A - methylating the DNA at the sites that the enzyme recognizes

DNA methylation is a process by which methyl groups are added to the DNA molecule. Methylation can change the activity of a DNA segment without changing the sequence. DNA methylation typically acts to repress gene transcription.

Q2: An animal, that has gained new genetic information from the acquisition of foreign DNA, is considered as

A a chimera

B a transgenic animal

C a vector

D an enzyme that links DNA molecules

ANS:B - a transgenic animal

Transgenic animals are genetically modified organisms. The first t.cow is Rosie whose milk have good nutritional quality than local. The first t.sheep is Doly and t. monkey is Andi.

Q3: In genetic engineering, a chimera is

A an enzyme that links DNA molecules

B a plasmid that contains foreign DNA

C a virus that infects bacteria

D a fungi

ANS:B - a plasmid that contains foreign DNA

Recombinant DNA is the general name for taking a piece of one DNA, combining it with another strand of DNA.

Recombinant DNA molecules are sometimes called chimeric DNA, because they are usually made of material from two different species, like the mythical chimera.

Q4: A genomic library is

A a database where the sequence of an organism's genome is stored

B a collection of many clones possessing different DNA fragments from the same organisms bound to vectors

C a book that describes how to isolate DNA from a particular organism

D a place where the information of the genetic organization of organisms are kept.

ANS:B - a collection of many clones possessing different DNA fragments from the same organisms bound to vectors

Genomic libraries are a catalog of genes of a particular organism. They are also commonly referred to as gene banks. To create a genomic library, the complete genome of an organism is cleaved into fragments and inserted into a cloning vector. It can also refer to the collection of vector molecules.

Q5: Which of the following is not commonly used as vector?

A Artificial chromosome

B Cosmid

C Fungi

D Plasmid

ANS:C - Fungi

In the above options fungi is the living organism. A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds.

Q6: Enzymes that recognize and cleave specific 4 to 8 base pair sequences of DNA are

A DNA ligase

B helicases

C restriction endonucleases

D DNA gyrase

ANS:C - restriction endonucleases

DNA Ligase is an enzyme that combines the two adjacent strands.

Helicases is another type of enzyme that cleaves hydrogen bonds present between two polynucleotide strands and it cleaves the entire duplex.

DNA gyrase involves in Negative super coiling after the action of Helicase enzyme.

Restriction endonuclease is an enzyme that cuts double stranded DNA, which makes incisions, one through each of the phosphate back bones of the double helix forming free 3'-OH and 5' phosphate ends. It recognizes and cleave specific 4 to 8 base pair sequences of DNA.

Q7: The advantage of using DNA polymerases from thermophilic organisms in PCR is that

A the DNA polymerases of these bacteria are much faster than those from other organisms

B the DNA polymerases of these bacteria can withstand the high temperatures needed to denature the DNA strands

C the DNA polymerases of these bacteria never make mistakes while replicating DNA

D all of the above

ANS:B - the DNA polymerases of these bacteria can withstand the high temperatures needed to denature the DNA strands

The polymerase chain reaction is a thermo-cycling process involving high temperature as 94°C, DNA polymerase of thermophilic bacteria can survive such temperature. An example is a commonly used Taq-polymerase enzyme isolated from Thermophylus aquatics.

Q8: Electroporation is

A the process of separating charged molecules through a gel maintained in an electric field

B the process of combining foreign DNA to an electrically charged vector molecule

C the application of high voltage pulses

D the process of multiplication of the cells

ANS:C - the application of high voltage pulses

Option A) is the definition of electrophoresis.

Option B) is incorrect because the vector molecule cannot be charged in electroporation.

Option D) is the basic definition of cell division so the answer is definitely option C) because electroporation is applying a high voltage pulse to create a temporary pore in the plasma membrane of the cell for introducing the foreign DNA.

Q9: The piece of equipment, that introduces DNA into cells via DNA-coated microprojectiles is known as

A laser

B DNA probe

C gene gun

D inoculating needle

ANS:C - gene gun

Gene gun is the method of introducing gene without using any vector in a plant cell;genes are bombarded on the cell with gold and tungsten.

Q10: The Southern blotting technique depends on

A similarities between the sequences of probe DNA and experimental DNA

B similarities between the sequences of probe RNA and experimental RNA

C similarities between the sequences of probe protein and experimental protein

D the molecular mass of proteins

ANS:A - similarities between the sequences of probe DNA and experimental DNA

Southern blot for DNA.
Northern blot for RNA.
Western blot for protein.
Eastern blot for PTM.

Q11: The deliberate modifications of an organism's genetic information by directly changing its nucleic acid content is a subject matter of

A genetic engineering

B population genetics

C microbiology

D protein engineering

ANS:A - genetic engineering

Genetic engineering is the alteration of genetic code by artificial means, and is therefore different from traditional selective breeding.

Q12: Agrobacterium tumefaciens is

A a disease in humans that causes loss of sight

B a bacterium that can be used to introduce DNA into plants

C a fungi that is used to produce antibiotics in large amounts

D a disease in humans that causes loss of weight

ANS:B - a bacterium that can be used to introduce DNA into plants

It is a gram-negative soil bacteria, responsible for producing crown gall disease, it is basically present in a wound or cut part of trees.

Q13: Which of the following enzyme is used to covalently bond foreign DNA to a vector plasmid?

A DNA polymerase

B Restriction endonuclease

C DNA ligase

D DNA helicase

ANS:C - DNA ligase

DNA ligase is the enzyme that join foreign DNA to vector plasmid by catalyzing the formation of a phosphodiester bond.

Q14: Which type of restriction endonuclease cuts the DNA within the recognition site?

A Type I

B Type II

C Type III

D All of the these

ANS:B - Type II

Type I enzymes cleave at sites remote from a recognition site.

Type II enzymes cleave within or at short specific distances from a recognition site. The most common Type II enzymes are HhaI, HindIII, and NotI, that cleave DNA within their recognition sequences.

Type III enzymes cleave at sites a short distance from a recognition site.

Type IV enzymes target modified DNA, Eg. Methylated, hydroxymethylated and glucosyl hydroxymethylated DNA.

Q15: Which of the following vector can maintain the largest fragment of foreign DNA?


B Cosmid

C Plasmid

D Phage


A yeast artificial chromosome (YAC) is a vector used to clone DNA fragments larger than 100 kb and up to 3000 kb. YACs are useful for the physical mapping of complex genomes and for the cloning of large genes.A YAC is built using an initial circular plasmid, which is typically broken into two linear molecules using restriction enzymes; DNA ligase is then used to ligate a sequence or gene of interest between the two linear molecules, forming a single large linear piece of DNA.

Q16: Vectors are

A molecules that degrade nucleic acids

B molecules that help in replication

C molecules that are able to covalently bond to and carry foreign DNA into cells

D molecules that protect host cells from invasion by foreign DNA

ANS:C - molecules that are able to covalently bond to and carry foreign DNA into cells

Vectors are nothing but a vehicle which is used for the transfer of gene. It is in the vector that the desired gene is inserted and it is then targeted to the host organism where it integrtes and replicates.

Q17: Charged molecules are separated based on varying rates of migration through a solid matrix when subjected to an electric field. This technique is known as

A photoreactivation

B gel electrophoresis

C autoradiography

D blotting

ANS:B - gel electrophoresis

Gel electrophoresis is a method for separation and analysis of macromolecules (DNA, RNA and proteins) and their fragments, based on their size and charge. Gel Electrophoresis is a process where an electric current is applied. Here, shorter molecules move faster because they migrate more easily through the pores of the gel. This phenomenon is called sieving. Proteins are separated by charge in agarose because the pores of the gel are too large to sieve proteins.

Gel electrophoresis can also be used for separation of nanoparticles.

Q18: A molecular technique in which DNA sequences between two oligonucleotide primers can be amplified is known as

A southern blotting

B northern blotting

C polymerase chain reaction

D DNA replication

ANS:C - polymerase chain reaction

PCR is a technique for amplifying DNA fragments which has three steps;

1. Ddenaturation
2. Annealing
3. Extension or elongation.

Q19: Problems in obtaining large amounts of proteins encoded by recombinant genes can often be overcome by using


B expression vectors


D all of these

ANS:B - expression vectors

Yes, but good vectors for cloning large DNA. But expression vectors are specific for the expression for an insered gene.

Q20: Which of the following is obtained using processed mRNA molecules as a template?






cDNA is a complementary DNA of processed m RNA.

In eukaryotes the gene is interrupted with introns (non coding regions) to obtain the desire target gene cDNA is used for further processing. That's why these processed m RNA (without introns) is used from which we make cDNA.

Q21: A short molecule containing 2-20 nucleotide is

A plasmid

B vector

C oligonucleotide

D mononucleotide

ANS:C - oligonucleotide

Oligonucleotides are short DNA or RNA molecules. Oligonucleotides as probe for the detection of DNA or RNA molecules by using procedure DNA microarray, southern blotting, FISH.

Q22: For gene probes to be useful they must

A be large enough to contain gene-specific sequences

B be labeled in some manner to allow detection

C both (a) and (b)

D none of the above

ANS:C - both (a) and (b)

Gene probe or DNA probe is used by Genetic engineering to search a specific genes. So it should be large enough to contain gene-specific sequences.

The probe has a base sequence complementary to the target sequence and will thus attach to it by base pairing. By labelling the probe with a radioactive isotope it can be identified on subsequent separation and purification.

Q23: What is the normal role of restriction endonucleases in bacterial cells?

A To degrade the bacterial chromosome into small pieces during replication

B To degrade invading phage DNA

C To produce RNA primers for replication

D All of the above

ANS:B - To degrade invading phage DNA

Option A) violates the significance of replication. Broken pieces of DNA ceases replication process if not ligated quickly.

Option C) also incorrect because RNA primers are synthesized by primase and not by res. Endonucleases and so it is obvious that option D) can also be ruled out.

Option B) is correct because the biological role of these enzymes is in restriction-modification (R-M) systems that have evolved to cleave the bacteriophage DNA injected into the cell and thus act as a defence mechanism against phage infection.

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