Question

Description of the characteristics of enzyme restriction endonuclease is given in following statements. Which of these is incorrect?

• A. The enzyme recognizes specific palindromic nucleotide sequences in the DNA.
• B. The enzyme cuts the sugar-phosphate backbone at specific sites on each strand.
• C. The enzyme binds DNA at specific sites and cuts only one of the two strands.
• D. The enzyme cuts DNA molecules at identified position within the DNA.

Answer 1

The correct option is C

The enzyme binds DNA at specific sites and cuts only one of the two strands.

The correct option is C.

Explanation of the correct option:

1. The restriction enzyme is a protein produced by bacteria that cleaves the DNA at specific sites. This site is known as the restriction site.
2. The enzyme endonuclease is known to bind at specific sites and cuts both the DNA (Deoxyribonucleic acid) strands.
3. Restriction enzymes are also called biological scissors or molecular scissors.
4. There are three kinds of restriction endonucleases which are categorized as Type I, Type II, and Type III.
5. These restriction enzymes cut the DNA far from the recognition sequences. However, they do not produce discrete restriction fragments, hence, are of not much practical value.
6. These enzymes cut at specific positions closer to or within the restriction sites. Discrete restriction fragments and gel banding patterns are observed. They are exclusively used for DNA analysis and gene cloning in the laboratories.
7. These are multi-functional proteins with two subunits- Res and Mod. It is a modification methyltransferase. The DNA sequence specific for the system is recognized by the Mod subunit.

Explanation of the incorrect options:

Option A:

1. The enzyme is known to recognize specific palindromic nucleotide sequences in the DNA.
2. Palindromic sequences are the sequences of nucleotides in double-stranded DNA or RNA, where the sequence of the first strand of DNA is similar to the sequences of the complementary strand when it is read from the same direction.

Option B:

1. The enzyme is known to cut the sugar-phosphate backbone at specific sites on each strand.
2. The sugar-phosphate backbone joins the nucleotides in a DNA and thus is available for cleavage.

Option D:

1. The enzyme cuts DNA molecules at an identified position within the DNA.
2. The Type I restriction enzyme is found to cut the DNA at a distance away from the recognition sequence.
3. The Type II restriction enzymes cleave the sugar-phosphate backbone at both sides of the recognition sequence.
4. The Type III restriction endonuclease cleaves the sugar-phosphate backbone at a non-palindromic sequence and needs two inversely oriented recognition sites for the cleavage.

Final answer: The enzyme endonuclease does not cut only one strand of the DNA molecule.