Biology Major Field Test Practice

Restriction enzymes, also known as restriction endonucleases, play a crucial role in molecular biology by cutting DNA at specific sequences known as recognition sites. The correct choice highlights that these enzymes recognize and cleave precise 4- to 8-base pair sequences within the DNA. This specificity allows restriction enzymes to differentiate between various DNA strands, ensuring that they only target specific sequences, which is fundamental in techniques like cloning and DNA manipulation.

The binding and activity of these enzymes depend on the sequence context; they have distinct recognition sites that usually consist of palindromic sequences—meaning the sequence reads the same forward and backward on complementary strands. This precise recognition is critical for applications such as genetic engineering, where accurate cuts at specific locations are necessary.

The other options do not accurately describe the mechanism of restriction enzyme action. Scanning entire genomes randomly would be inefficient and ineffective for locating specific sequences. Modifying RNA structures is unrelated to the function of restriction enzymes, as these enzymes act specifically on DNA, not RNA. Lastly, the idea of binding to all nucleotides present does not reflect the selective nature of restriction enzymes, which only interact with their target sequences.