Biotechnology Principles and Processes PYQs

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During recombinant DNA purification, chilled ethanol is added to the sample to precipitate nucleic acids. Ethanol causes DNA to come out of solution as a solid because it reduces its solubility in water. This helps in collecting DNA by spooling it out. Hence, the correct option is DNA.

DNA precipitates as a visible, sticky mass when ethanol is added and the mixture is kept cold, aiding its collection by centrifugation.

“Ethanol precipitation is used to precipitate DNA during purification.”

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The correct sequence is B, C, D, A. First, B: restriction enzymes cut DNA at specific locations. Next, C: the desired DNA fragment is isolated from the rest. Then, D: the gene is amplified using PCR to obtain enough copies. Finally, A: the recombinant DNA is inserted into the host cell for expression. This order reflects the typical steps described in NCERT for recombinant DNA technology, from cutting to isolating, amplifying, and inserting into a host.

PCR stands for polymerase chain reaction and helps make many copies of the gene of interest before insertion.

Restriction enzymes cut DNA; isolate the fragment; amplify the gene; insert into host cells.

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Probe is not a cloning vector. Cloning vectors are DNA molecules used to carry foreign DNA into a host cell for replication, such as plasmids (pBR322) and larger artificial chromosomes like BACs and YACs. Probes are short DNA sequences used to detect specific DNA via hybridization, not to replicate DNA in a host. Hence option 1 is correct.

pBR322 is a classic plasmid vector used in cloning experiments; BACs can carry large DNA fragments in bacteria; YACs can clone large fragments in yeast cells.

Vectors used for cloning include plasmids (like pBR322) and artificial chromosomes (BAC, YAC); probes are for detection, not cloning.

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Option 3 is not true. In gel electrophoresis, DNA is visualized using dyes such as ethidium bromide, which after UV illumination shows bright orange fluorescence. A chromogenic substrate does not produce blue DNA bands in this technique. The statements 1, 2, and 4 are correct: elution refers to extracting DNA strands from the gel, DNA fragments are stained with ethidium bromide, and under UV light, ethidium bromide–stained DNA bands appear orange.

Ethidium bromide is a common DNA stain used in gel electrophoresis because it binds DNA and fluoresces under UV light, making the fragments visible.

Gel electrophoresis visualization relies on ethidium bromide staining and UV light to see orange fluorescent DNA bands; chromogenic blue bands are not part of this method.

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Only option 2 shows a perfect palindromic sequence: 5' GAATTC 3' matches 3' CTTAAG 5' as its reverse complement. This is the recognition site for the restriction enzyme EcoRI, which cuts between G and A to yield sticky ends. Other options are not true palindromes (the sequences do not read the same in the opposite direction on the complementary strand), so they are not typical EcoRI sites. NCERT emphasizes that restriction enzymes recognize palindromic sequences and cut within them to produce sticky or blunt ends.

Palindromic DNA sequences read the same forward on one strand and backward on the complementary strand, enabling precise enzymatic cuts.

Palindromic sequences are read the same in the 5'→3' direction on both strands and are common recognition sites for restriction enzymes.

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Statement I is correct: Restriction endonucleases recognize specific palindromic nucleotide sequences. Statement II is also correct: these enzymes cut the DNA within the recognition site, often a little away from the center of the palindromic sequence, producing "sticky" or blunt ends as described in NCERT. Thus, both statements are correct.

Most Type II restriction enzymes cut within or near the palindromic target, enabling precise genetic manipulation for cloning experiments.

Restriction endonucleases recognize palindromic sequences and cut within those sites, often not exactly at the center.

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According to NCERT, a cloning vector should have features that allow easy selection and replication: a marker gene, and an origin of replication. A single restriction site or a well-structured multiple cloning site (but not multiple unwanted sites) helps controlled insertion. The statement that is not desirable is having two or more recognition sites, because multiple sites can cause unwanted cuts and incorrect insertion, reducing cloning efficiency. Therefore, option 3 is correct.

Cloning vectors use restriction enzymes to open DNA at specific sites; selective markers help identify cells that have taken up the vector.

A vector should contain a marker gene and an origin of replication for selection and propagation.