CUET Preparation Today
Which of the following statements is true about exonucleases? |
They cut DNA at specific internal sequences. They remove nucleotides from the ends of DNA. They add methyl groups to DNA. They do not participate in DNA modification. |
They remove nucleotides from the ends of DNA. |
The correct answer is Option (2) -They remove nucleotides from the ends of DNA. Restriction Endonucleases (Molecular Scissors): These are enzymes that are commonly referred to as "molecular scissors" because they cut DNA molecules at specific recognition sequences. These recognition sequences are often palindromic, meaning the sequence reads the same forwards and backward. Restriction enzymes belong to a larger class of enzymes called nucleases. These are of two kinds; exonucleases and endonucleases. Exonucleases remove nucleotides from the ends of the DNA whereas, endonucleases make cuts at specific positions within the DNA. Today we know more than 900 restriction enzymes that have been isolated from over 230 strains of bacteria each of which recognise different recognition sequences. The first restriction endonuclease is –Hind II. EcoRI and Hind III are also restriction endonuclease .EcoRI comes from Escherichia coli RY 13. |
