Recognition sequence for a restriction enzyme is usually what type?

Correct answer: Fixed short DNA sequence

The direct answer is B: a fixed short DNA sequence. A restriction enzyme is a protein that cuts DNA at, or near, a particular recognition site. The site is made of a specific order of nucleotides, not a random stretch of DNA. Step by step: DNA contains a long sequence of nucleotide bases; the enzyme recognizes a particular short pattern; it binds to that pattern; it cuts the DNA at a defined position; this produces predictable fragments. Many commonly studied recognition sites are palindromic, meaning the sequence reads similarly in the required direction on the two complementary strands, though the key idea in this question is fixed and short DNA recognition. Option A, a very long protein, describes neither the recognition site nor the usual target. The enzyme itself is a protein, but the question asks about its recognition sequence. Option C, a fat layer, is not genetic material. Option D, a mineral particle, also cannot be a DNA base sequence. Option B is correct because specificity comes from matching the enzyme with a particular nucleotide pattern. Memory cue: restriction enzyme means molecular scissors with a DNA address.