Question

Restriction endonucleases are enzymes which
A. Recognize a specific nucleotide sequence for binding of DNA ligase
B. Restrict the action of the enzyme DNA polymerase
C. Remove nucleotides from the ends of the DNA molecule
D. Makes cut at a specific position within the DNA molecule

Answer 1

Hint: Endonucleases are classes of enzymes which cleave the phosphodiester bonds within a polynucleotide chain. They cleave DNA internally, which means they do not require free DNA ends for activity.

Complete answer:
Option A: DNA ligases are responsible for repairing breaks in the DNA. It recognizes the site of the break and joins the strands together by the formation of phosphodiester bonds. Therefore, this is the incorrect option.

Option B: DNA polymerases are enzymes that carry out the synthesis of new DNA. They read the template DNA fragment and add complementary nucleotides, one at a time. DNA polymerase adds nucleotides to the 3’ end of the DNA strand. Therefore, this is the incorrect option.

Option C: The removal of nucleotides from the ends of DNA molecules is carried out by a class of enzymes known as DNA exonucleases. They require a free end of DNA for activity. They cleave the phosphodiester bonds between nucleotides and remove nucleotides from the strand, one at a time.
Therefore, this is the incorrect option.

Option D: Restriction Endonucleases are responsible for making cuts at specific sites within the DNA molecule. It helps in the fragmentation of DNA. The sites at which they cut are called recognition sites, which are a specific nucleotide sequence. The recognition sites are usually palindromic nucleotides. Each restriction endonucleases have specific recognition sites. Because of this property, they are an important tool in biotechnology. Therefore this is the correct answer.

Hence, the correct answer is option (D)

Note: Restriction endonucleases are found in bacteria and archaea. They are isolated and used in laboratories to manipulate DNA.
They are used during gene cloning. Plasmid vectors are cut at specific restriction sites using restriction endonucleases and the gene of interest is inserted into this site with the help of ligase.