Biotechnology - Principles and Processes
10 solved NEET Biology previous year questions on Biotechnology - Principles and Processes, each with the correct answer and a full explanation.
Q1
The restriction enzymes are used in genetic engineering, because:
✓ Correct answer: a) they can cut DNA at specific base sequence.
ExplanationRestriction enzymes, also known as molecular scissors, are essential in genetic engineering because they have the unique ability to cut DNA at specific base sequences.These enzymes recognize a particular sequence of nucleotides, usually a palindromic sequence, and break the phosphodiester bonds at that exact location.This precision allows scientists to isolate specific genes or create "sticky ends" that can later be joined with other DNA fragments.In contrast, they do not cut at variable sites, nor do they degrade proteins or join DNA; joining is the job of an enzyme called DNA ligase.
Q2
Given below is a sample of a portion of DNA strand giving the base sequence on the opposite strands. What is so special shown in it? _________GAATTC ________ __________ CTTAAG ________
✓ Correct answer: d) Palindromic sequence of base pairs
Explanation(4) Each restriction endonuclease recognises a specific palindromic nucleotide sequences in the DNA.The palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same. [New NCERT Class 12th Page no.196]
Q3
Which of the following in not a feature of the plasmids?
✓ Correct answer: c) Single-stranded
ExplanationPlasmids are typically circular, transferable, and capable of independent replication.However, they are generally double-stranded DNA molecules, not single-stranded.Therefore, single-stranded is not a characteristic of plasmids.
Q4
In a mixture, DNA fragments are separated by
✓ Correct answer: b) Electrophoresis
ExplanationDNA fragments in a mixture can be separated on the basis of their size by a technique known as gel electrophoresis.In this techniques, DNA samples are loaded into wells (indentations) at one end of a gel, and an electric current is applied to pull them through the gel.DNA fragments are negatively charged, so they move towards the positive electrode.
Q5
During the purification process for recombinant DNA technology, addition of chilled ethanol precipitates out [NEET 2021]
✓ Correct answer: d) DNA
ExplanationDuring the purification process in recombinant DNA technology, chilled ethanol is added to the extracted genetic material to precipitate DNA.Ethanol reduces the solubility of DNA, causing it to form visible fine threads that can be collected by spooling.This step helps in isolating pure DNA for further genetic manipulation.
Q6
During the process of gene amplification using PCR, if very high temperature is not maintained in the beginning, then which of the following steps of PCR will be affected first?
✓ Correct answer: b) Denaturation
ExplanationPolymerase chain reaction (PCR) involves 3 steps: denaturation, annealing and elongation.The denaturation process requires high temperature of about .DNA fragments are joined with the help of DNA ligase enzyme.During annealing, primers bind to the target DNA sequences and initiate polymerisation.This process is performed at .Addition of nucleotides to the primer, synthesises a new DNA with the help of enzyme DNA polymerase.This step is called elongation which is performed at .
Q7
Hind II always cuts DNA molecules at a particular point called recognition sequence and it consists of: [NEET 2024]
✓ Correct answer: d) 6 bp
ExplanationHind II was the first restriction endonuclease discovered that cuts DNA at a specific site — known as a recognition sequence.This recognition sequence is 6 base pairs (bp) long and is palindromic, meaning the sequence reads the same on both strands in the 5′ → 3′ direction.Hind II recognizes a specific 6-bp sequence and cuts DNA within this site, producing blunt ends.
Q8
Plasmid pBR322 has PstI restriction enzyme site within gene that confers ampicillin resistance, If this enzyme is used for inserting a gene for -galactoside production and the recombinant plasmid is inserted in an E.coli strain
✓ Correct answer: d) It will not be able to confer ampicillin resistance to host cell.
ExplanationCorrect answer: Option D Explanation: In plasmid pBR322, the PstI restriction site lies within the ampicillin resistance gene (ampR).When a foreign gene (here, the gene for β-galactoside production) is inserted at this site, it disrupts the ampR gene.This process is called insertional inactivation.As a result: The recombinant plasmid cannot express ampicillin resistance.The transformed E. coli cells will not survive on ampicillin-containing medium, even though they may produce β-galactoside.Therefore, the correct option is D: It will not be able to confer ampicillin resistance to host cell.
Q9
DNA precipitation out of a mixture of biomolecules can be achieved by treatment with
✓ Correct answer: b) Chilled ethanol
ExplanationThe correct answer is Option B — Chilled ethanol.Explanation: During DNA isolation, after removing proteins, RNA, and other biomolecules, DNA is precipitated out of the solution by adding chilled ethanol.DNA is insoluble in cold alcohol, so it separates out as fine white threads that can be spooled or collected.The low temperature enhances precipitation and prevents DNA degradation.Isopropanol can also precipitate DNA but NCERT specifically mentions chilled ethanol for DNA precipitation.Methanol at room temperature and chloroform are not used for DNA precipitation.Therefore, the correct choice is chilled ethanol.
Q10
Choose the correct pair from the following. [NEET 2020]
✓ Correct answer: a) Ligases - Join the two DNA molecules
ExplanationLigases are enzymes that play a crucial role in molecular biology by catalyzing the joining of two DNA molecules.They create phosphodiester bonds between adjacent nucleotides, sealing breaks or nicks in the DNA backbone.This process is fundamental in genetic engineering and molecular cloning, facilitating the construction of recombinant DNA molecules.Ligases are essential for linking donor DNA fragments with vectors, enabling the production of genetically modified organisms or the amplification of specific DNA sequences.
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