Which enzyme cuts DNA at a specific recognition sequence and is therefore called molecular scissors?
- A.DNA ligase
- B.Restriction endonuclease
- C.DNA polymerase
- D.Reverse transcriptase
Correct answer
Explanation
The correct answer is B, restriction endonuclease. A restriction endonuclease recognises a short palindromic sequence in DNA and cuts both strands there, leaving sticky ends that can pair with another piece cut by the same enzyme; Hind II was the first such enzyme to be discovered and EcoRI from Escherichia coli is the most widely used. Option A, DNA ligase, does the opposite work: it seals the gene into the vector and is therefore called molecular glue. Option C, DNA polymerase, builds a new strand along a template and is used in the polymerase chain reaction, where the heat stable Taq polymerase is employed. Option D, reverse transcriptase, makes DNA from an RNA template and is used to prepare complementary DNA and in the replication of retroviruses. Pair the enzymes with their verbs: cut, join, copy and reverse copy.
Read the full article: Biotechnology and Its Applications: Notes and PYQs
Practice Questions
View allWhich bacterium is used as a natural vector to transfer genes into plant cells?
- A.Escherichia coli
- B.Agrobacterium tumefaciens
- C.Bacillus thuringiensis
- D.Rhizobium leguminosarum
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This soil bacterium naturally transfers a part of its tumour inducing plasmid, called the Ti plasmid, into the cells of a dicotyledonous plant and causes crown gall disease; genetic engineers disarm the plasmid, insert the gene they want and use the bacterium as a vector, which is why it is…
Read the full explanation →The insect resistance gene of Bt cotton is obtained from which organism?
- A.A virus
- B.A soil bacterium
- C.A fungus
- D.An alga
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The genes called cry genes are taken from Bacillus thuringiensis, a bacterium of the soil that forms protein crystals during its spore stage.
Read the full explanation →Golden Rice is a genetically modified variety enriched with which substance?
- A.Iron
- B.Beta carotene
- C.Lysine
- D.Vitamin C
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Golden Rice carries genes that let the grain make beta carotene, the orange pigment that the human body converts into vitamin A, and the colour of the grain gives the variety its name; the aim is to reduce night blindness and childhood blindness in populations whose diet is mainly rice.
Read the full explanation →Which heat stable enzyme is used in the polymerase chain reaction?
- A.Taq polymerase
- B.DNA ligase
- C.EcoRI
- D.Lysozyme
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The polymerase chain reaction repeats three steps, denaturation at a high temperature, annealing of short primers and extension of the new strand, so the enzyme must survive near boiling water; Taq polymerase, obtained from the bacterium Thermus aquaticus of hot springs, does exactly that and lets a single DNA segment…
Read the full explanation →Dolly, the first mammal cloned from an adult somatic cell, was which animal?
- A.A cow
- B.A sheep
- C.A goat
- D.A monkey
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Dolly was a sheep produced at the Roslin Institute in Scotland in 1996 by the technique of somatic cell nuclear transfer, in which the nucleus of an udder cell of one sheep was placed in an egg whose own nucleus had been removed, so the lamb carried the genes of…
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