Which of the following statements is/are associated with role of enzymes in genetic engineering? 1. Exonucleases remove nucleotides from the ends of DNA 2. Restriction endonucleases are used to form recombinant molecule of DNA Select the answer using the code given below:
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Correct answer
Explanation
The correct answer is C, Both 1 and 2. Both statements describe how nucleases are used as tools of recombinant DNA technology.
Nucleases are enzymes that break the phosphodiester bonds of DNA. Exonucleases work from the ends of a DNA strand and remove nucleotides one by one. Endonucleases cut at positions inside the strand. Restriction endonucleases, the "molecular scissors", recognise a specific palindromic base sequence and cut there, often leaving sticky ends. When the same enzyme cuts a plasmid vector and foreign DNA, the matching sticky ends can be joined by DNA ligase, giving a recombinant DNA molecule made of DNA from two different genomes. The first such enzyme studied in detail was EcoRI from E. coli.
Option A is wrong because it leaves out statement 2, which is the very basis of gene cloning. Option B is wrong because statement 1 is also correct; exonucleases do trim DNA from its ends. Option D is wrong because both statements are true.
Exam tip: restriction enzyme cuts, DNA ligase joins, plasmid carries; exonuclease works at ends, endonuclease works inside.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
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- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
Show answer
They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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