11 public questions tagged with this topic.
Restriction enzymes are molecular scissors that cut DNA at specific recognition sites, which is essential_x000D_ for genetic engineering.
Ref: NCERT Class 12 Biology Chapter 10: Biotechnology and its Applications Biopiracy and Biopatent - Basmati Turmeric Neem
Restriction endonucleases recognize specific sequences in DNA and cut at precise locations, facilitating genetic modifications.
Ref: NCERT Class 12 Biology Chapter 9: Biotechnology: Principles and Processes Bioreactors and Downstream Processing
Recombinant DNA technology allows the insertion of foreign genes into another organism to produce desirable traits or proteins.
Ref: NCERT Class 12 Biology Chapter 9: Biotechnology: Principles and Processes Tools - Restriction Enzymes - Molecular Scissors
Recombinant DNA technology enables the insertion of foreign genes into host cells for genetic engineering and medical applications.
Ref: NCERT Class 12 Biology Chapter 9: Biotechnology: Principles and Processes Principles of Biotechnology - Genetic Engineering
Inverse polymerase chain reaction based mutagenesis allows mutation of entire plasmid without subcloning. Divergent primers containing desired change amplify around circular template generating linear mutated product. Reaction mixture retains original non-mutated parental plasmid isolated from methylation-competent Escherichia coli, which could transform and cause background wild-type colonies. DpnI is a restriction endonuclease that recognizes methylated and hemimethylated sequence 5 prime GATC methylated at adenine by Dam methylase. It cleaves parental methylated DNA into fragments unable to replicate, enriching for newly synthesized unmethylated mutated plasmid, increasing mutagenesis efficiency and reducing false positives.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Molecular linkers are blunt-ended synthetic double-stranded oligonucleotides containing one or more internal restriction sites. After ligation to blunt-ended target DNA with T4 DNA ligase, digestion with corresponding restriction enzyme exposes cohesive termini for cloning. Adaptors are asymmetric duplexes engineered with one blunt end and one pre-formed sticky end; they require no post-ligation restriction cleavage, as cohesive overhang is built in. Adaptors reduce risk of linker oligomerization and self-ligation, improving efficiency. Both strategies facilitate addition of new restriction sites and conversion of blunt fragments into insertable modules for plasmid construction.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Homopolymer tailing overcomes incompatibility of blunt ends by enzymatically synthesizing complementary extensions. Terminal deoxynucleotidyl transferase adds homopolymer tracts such as poly-deoxyguanosine to vector 3' ends and poly-deoxycytosine to insert ends. Guanine-cytosine pairing provides high thermal stability due to three hydrogen bonds, enabling annealed complexes to be extended or ligated and subsequently repaired in vivo. Alternative dA-dT tailing is also used. Before advent of synthetic linkers, this method was central to first cDNA cloning experiments, demonstrating conversion of blunt molecules into clonable sticky structures without restriction site dependence.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Terminal deoxynucleotidyl transferase, also called TdT, is a unique template-independent DNA polymerase expressed in pre-B and pre-T lymphocytes where it adds N-nucleotides during V(D)J recombination. In vitro, it catalyzes addition of deoxyribonucleotides preferentially to the 3'-hydroxyl terminus of single or double-stranded DNA, extending the strand without a complementary template. This property underlies homopolymer tailing for cDNA cloning, 3'-end labeling with dideoxynucleotides, and generation of sticky ends from blunt fragments, as poly-A and poly-T tails can anneal to facilitate recombinant construction.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Neoschizomers recognize the same nucleotide sequence but hydrolyze phosphodiester bonds at different positions, thereby generating distinct fragment ends. Discrimination between isoschizomers, neoschizomers and isocaudomers is essential for mapping. HpaII and MspI both recognize CCGG, representing canonical tetranucleotide containing CpG methylation sensitivity. HpaII cleaves C/CGG, producing 5' CG overhang, while MspI is often taught as cutting at C/CGG as well but historic textbook classifications list them as neoschizomers due to differing cleavage sensitivity and context-specific cut variations. Their shared recognition with divergent cutting behavior exemplifies neoschizomer definition used in examinations.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Linkers are short double-stranded blunt-ended oligonucleotides containing one or more restriction enzyme recognition sites. They are ligated to blunt-ended DNA fragments and then digested with cognate restriction enzyme to create cohesive ends. Adapters already possess a blunt end and a pre-formed sticky end, so no digestion after ligation is necessary. Thus the distinguishing feature of linkers is requirement for restriction cleavage post-ligation to expose sticky termini, which risks concatemer formation and insert cleavage if internal sites exist, unlike ready-to-use adapter strategy.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Labeling cohesive ends commonly employs DNA polymerases that can fill in 5' overhangs. T4 DNA polymerase possesses strong 3' to 5' exonuclease and polymerase activity that efficiently incorporates labeled dNTPs opposite the single-stranded overhang using the protruding 5' sequence as template. EcoRI is restriction enzyme that creates ends, not label them. Ligase joins fragments, exonuclease III degrades from 3' terminus. Hence T4 polymerase is standard choice for labeling sticky ends in mapping, footprinting, and terminal labeling protocols using radioactive or fluorescent nucleotides.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
