Restriction sites are typically identified by palindromic sequences. Which description matches a restriction site?

Restriction sites are typically identified by palindromic sequences. Which description matches a restriction site?

• A. The same sequence read 5' to 3' on both strands (palindromic)
• B. A random sequence
• C. A sequence found only in RNA
• D. A sequence with high GC content

Answer: (A)

Restriction sites for restriction enzymes are short sequences in double-stranded DNA that are read the same in the two opposite orientations, making them palindromic. This symmetry matters because the enzyme binds as a dimer to the site and interacts with bases on both strands in a complementary, mirrored way, so a single site can be recognized reliably from either direction. A classic example is GAATTC, which is palindromic: on the opposite strand the complement is CTTAAG, and reading that strand from 5′ to 3′ recovers GAATTC as well. This shared, mirrored sequence allows the enzyme to cut at a precise location within the site. Reasons the other descriptions don’t fit: a random sequence isn’t specifically recognized by restriction enzymes, so it wouldn’t reliably indicate a restriction site; a sequence found only in RNA isn’t relevant because restriction enzymes act on DNA, not RNA; a sequence with high GC content isn’t a defining feature of a restriction site—while some sites may be GC-rich, the essential attribute is the palindromic, double-stranded nature that enables symmetrical recognition and cutting.

Restriction sites for restriction enzymes are short sequences in double-stranded DNA that are read the same in the two opposite orientations, making them palindromic. This symmetry matters because the enzyme binds as a dimer to the site and interacts with bases on both strands in a complementary, mirrored way, so a single site can be recognized reliably from either direction. A classic example is GAATTC, which is palindromic: on the opposite strand the complement is CTTAAG, and reading that strand from 5′ to 3′ recovers GAATTC as well. This shared, mirrored sequence allows the enzyme to cut at a precise location within the site.

Reasons the other descriptions don’t fit: a random sequence isn’t specifically recognized by restriction enzymes, so it wouldn’t reliably indicate a restriction site; a sequence found only in RNA isn’t relevant because restriction enzymes act on DNA, not RNA; a sequence with high GC content isn’t a defining feature of a restriction site—while some sites may be GC-rich, the essential attribute is the palindromic, double-stranded nature that enables symmetrical recognition and cutting.