BIOLOGY Assertion (A) & Reason (B) MCQ

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

Plasmid pBR322 has a variety of unique restriction sites for restriction endonucleases. Two unique sites, Pst I andPvu /are located within the amp' gene and Bamrll, Sal I etc. are within tet¹ gene. The presence of restriction sites within the marker tef and amp' permits an easy selection for cell transformed with the recombinant pBR322. Insertion of the DNA fragment into the plasmid using enzyme Pst I and Pvu I places the DNA insert within the gene amp' and make it non functional.

2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.

3. Assertion is correct but Reason is incorrect.

Explanation:

Restriction enzymes were named due to the phenomenon of host restriction of bacterial phages.

Restriction enzymes produced in a bacterial cell, recognise and cleave foreign DNA introduced (such as from bacteriophage) into the cell.

Thus, bacterial cell cannot be infected and lysed by bacteriophage and hence a bacterial cell lacking restriction enzymes is easily susceptible to infection of phages.

The DNA of the host bacterial cell is protected from its own restriction endonucleases by methylation (usually of A and C) within their recognition sites.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Bacteriophage vector have two advantages over plasmid vectors.

1. They are more efficient than plasmids for the cloning of large DNA fragments. For example, the largest cloned insert in lambda phage is 24kb while for plasmid vector it is less than 15kb.
2. It is easier to screen a large number of phage plaques than bacterial colonies for identification of recombinant vectors.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Restriction endonuclease are enzymes that cleaves DNA at specific sites along the molecule. Type I restriction enzyme recognises specific DNA sequences but make their cut at seemingly random sites that can be as far as 1000 base pair away from the recognition site.

3. Assertion is true but reason is false.

Explanation:

Selectable markers are the substances which helps in identifying recombinants and eliminating non recombinants. Generally the genes encoding the resistance to antibiotics such as tetracycline, ampicillin, kanamycin or chloramphenicol, etc. are useful selectable markers for E.coli.

2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

Explanation:

A palindromic sequence in DNA is one in which the 5' to 3' base pair sequence is identical on both strands.

Restriction enzymes recognize and cut within specific palindromic sequences, known as restriction sites, in the DNA and produce DNA strands with the sticky ends. It cuts both the strands of DNA at the palindrome site.

This is usually a 4- or 6 base pair sequence. Hence the assertion and reason are both correct but the reason does not explain the given assertion.

3. Assertion is true but reason is false.

Explanation:

Restriction enzyme, a type of endonuclease, functions by "inspecting" the length of a DNA sequence. Once it finds a recognition sequence, it binds and cut each of the two strands of the double helix at specific point a staggered cut generates two sticky ends and a straight cut generates blunt end. The staggered cut leaving single stranded portions at the ends which results in overhanging stretches called sticky ends. These are named so because they form hydrogen bonds with their complementary counter parts, i.e., they can join similar complementary ends of DNA fragment from some other source with the help of DNA ligase. This stickiness of the ends facilitates the action of the enzyme DNA ligase, not DNA polymerase.

3. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

Yeast Artificial Chromosome (YACs) is a human engineered DNA molecule derived from the yeast. YACs are often used in connection with mapping and sequencing of genomes. Segments of an organism's DNA, upto one million base pairs in length, can be inserted into YACs. The YACs are then taken up by yeast cells. As the yeast cell grow and divide, they amplify the YAC DNA, which can be isolated and used for DNA mapping and sequencing.

4. Both assertion and reason are false.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

In recombinant DNA technology, widely used host for replication and amplification of recombinant DNA are prokaryotic E. coli and the eukaryotic yeast. They replicate very fast to form a large population which expressed desired gene. Yeast artificial chromosome (YAC) are important cloning tools for the analysis of complex genome such as that of humans. They allow the maintenance, propagation and analysis of such genome in an experimentally tractable system, the yeast.

1. Both assertion and reason are true and reason is the correct explanation of assertion.

Explanation:

The bacterial cell is made competent by treating it with specific concentration of a divalent cation such as calcium to increase the efficiency with which DNA can enter the bacteria through pores of cell wall because DNA is a hydrophilic molecule and it cannot pass through cell membrane so making bacterial cell competent ease the process to take up DNA.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

2. Both assertion and reason are true but reason is not the correct explanation of assertion.

Explanation:

DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA, because in these sequences, a small stretch of DNA is repeated many times. These sequences normally do not code for any proteins, but they form a large portion of human genome. These sequence show high degree of polymorphism and form the basis of DNA fingerprinting. As the polymorphisms are inheritable from parents to children, DNA fingerprinting is the basis of paternity testing in case of disputes.

2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

Explanation:

Polymerase chain reaction (PCR) has many applications in medicine.

This is a very sensitive test that is used to amplify trace amount of DNA or RNA located in or on any liquid or any surface where DNA strand can be deposited.

The HIV is difficult to target and eradicate. Earlier tests relied on presence of antibodies to the virus in the blood.

But they appear late and maternal antibodies mask the infection in newborn.

PCR test can detect as little as one viral genome among the DNA of over 50,000 host cells.

Suspected cases can be detected earlier, donated blood can be screened directly for the virus, newborns can be immediately tested for infection and treatment can be quantified.

PCR was first used for genetic testing. A sample of DNA was used for the presence of genetic disease mutations.

PCR can be used to amplify the sequence that contains mutation with appropriate restriction enzymes, generating 10 million copies.

The copies are used for further testing like endonuclease digestion with electrophoresis, hybridization to oligonucleotide probes, polymorphism analysis etc.

Prospective parents can be tested for being genetic carriers in hemophilia, thalassemia.

A child can be detected for actual disease.

PCR analysis is also essential to preimplantation genetic diagnosis, where individual cells of developing embryo are tested for the mutation.

3. Assertion is true but reason is false.

Explanation:

A palindromic sequence in DNA is one in which the 5' to 3' base pair sequence is identical on both strands. Restriction enzymes recognise and make a cut within specific palindromic sequence, known as restriction sites, in the DNA. This is usually a 4 or 6 base pair sequence.