3
Question
How many of the following statements regarding restriction enzymes are correct?
A. They generally recognise palindromic nucleotide sequences.
B. They are endonucleases.
C. They are isolated from viruses.
D. A particular restriction enzyme produces the same kind of sticky or blunt ends in any DNA molecules.
How many of the following statements regarding restriction enzymes are correct?
A. They generally recognise palindromic nucleotide sequences.
B. They are endonucleases.
C. They are isolated from viruses.
D. A particular restriction enzyme produces the same kind of sticky or blunt ends in any DNA molecules.
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Solution
The correct option is C 3
Nucleases are the class of enzymes that act on the nucleic acids (RNA and DNA) and digest them.
They are of two types - exonucleases and endonucleases.
- Exonucleases cleave phosphodiester bonds between consecutive nucleotides of the DNA at their terminal ends (either 5’ or 3’ end), usually one nucleotide at a time.
- Endonucleases are enzymes that make cuts between consecutive nucleotides within the DNA.
Restriction enzymes are a type of endonucleases that cleave the phosphodiester bonds present between consecutive nucleotides at or near to specific positions called ‘recognition sites’. The cleavage site is present within the DNA. They are also called “molecular scissors or biological scissors” because they cut the DNA and produce fragments.
The restriction endonuclease enzymes are mostly produced by the bacteria as a part of their defence mechanism. More than 900 restriction enzymes have been isolated from over 230 strains of bacteria each of which recognise different recognition sequences.
They can act on different DNA molecules if they have the recognition site for that particular restriction enzyme. The restriction enzyme would sometimes cut the sugar phosphate backbone in the double stranded DNA in such a way that it leaves single stranded free ends called sticky ends. Since same recognition sites, if present in different DNA molecules, can be identified by a particular restriction enzyme, hence, the same kind of sticky ends will be generated. Hence, for those restriction enzymes which cleave two different DNA molecules at specific sites within the recognition sequence, sticky overhangs generated would be identical.
Hence, statements A, B and D are correct. Statement C is incorrect as we do not isolate restriction enzymes from viruses.
Nucleases are the class of enzymes that act on the nucleic acids (RNA and DNA) and digest them.
They are of two types - exonucleases and endonucleases.
- Exonucleases cleave phosphodiester bonds between consecutive nucleotides of the DNA at their terminal ends (either 5’ or 3’ end), usually one nucleotide at a time.
- Endonucleases are enzymes that make cuts between consecutive nucleotides within the DNA.
The restriction endonuclease enzymes are mostly produced by the bacteria as a part of their defence mechanism. More than 900 restriction enzymes have been isolated from over 230 strains of bacteria each of which recognise different recognition sequences.
They can act on different DNA molecules if they have the recognition site for that particular restriction enzyme. The restriction enzyme would sometimes cut the sugar phosphate backbone in the double stranded DNA in such a way that it leaves single stranded free ends called sticky ends. Since same recognition sites, if present in different DNA molecules, can be identified by a particular restriction enzyme, hence, the same kind of sticky ends will be generated. Hence, for those restriction enzymes which cleave two different DNA molecules at specific sites within the recognition sequence, sticky overhangs generated would be identical.
Hence, statements A, B and D are correct. Statement C is incorrect as we do not isolate restriction enzymes from viruses.
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