What is the function of endonucleases?

To cut DNA at specific positions within the DNA

The correct answer is Option (2) - To cut DNA at specific positions within the 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. When a restriction endonuclease encounters its specific recognition sequence on a DNA molecule, it cleaves the DNA at that specific point by breaking the sugar-phosphate backbone of both DNA strands. This results in the production of DNA fragments with "sticky ends," which can be used in various molecular biology techniques like DNA cloning.

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. The function of endonucleases is to cut DNA at specific positions within the DNA molecule. Unlike exonucleases that remove nucleotides from the ends of DNA or RNA molecules.

Endonucleases are enzymes that recognize specific nucleotide sequences in the DNA called recognition sequences or recognition sites. These recognition sequences are typically palindromic, meaning they read the same on both strands of the double helix when read in the 5' to 3' direction. For example, a common recognition sequence for many restriction endonucleases is the palindromic sequence 5'-GAATTC-3', which reads the same on both strands as 5'-GAATTC-3'.

When an endonuclease recognizes its specific recognition sequence, it binds to the DNA at that site and then catalyzes the hydrolysis of the phosphodiester bond within the DNA backbone. This results in the cleavage of the DNA into two fragments at the specific position dictated by the recognition sequence.