Respuesta :
Answer:
the answer is transposes.
Explanation:
Transposons, also called transposable elements, are mobile genetic elements that generally have only modest target site selectivity and can thus insert themselves into many different DNA sites. In transposition, a specific enzyme, usually encoded by the transposon and called a transposase, acts on a specific DNA sequence at each end of the transposon—first disconnecting it from the flanking DNA and then inserting it into a new target DNA site. There is no requirement for homology between the ends of the element and the insertion site.
Most transposons move only very rarely (once in 105 cell generations for many elements in bacteria), and for this reason it is often difficult to distinguish them from nonmobile parts of the chromosome. In most cases, it is not known what suddenly triggers their movement.
On the basis of their structure and transposition mechanisms, transposons can be grouped into three large classes (Table 5-3), each of which is discussed in detail in subsequent sections. Those in the first two of these classes use virtually identical DNA breakage and DNA joining reactions to translocate. However, for the DNA-only transposons, the mobile element exists as DNA throughout its life cycle: the translocating DNA segment is directly cut out of the donor DNA and joined to the target site by a transposase. In contrast, retroviral-like retrotransposons move by a less direct mechanism. An RNA polymerase first transcribes the DNA sequence of the mobile element into RNA. The enzyme reverse transcriptase then transcribes this RNA molecule back into DNA using the RNA as a template, and it is this DNA copy that is finally inserted into a new site in the genome. For historical reasons, the transposase-like enzyme that catalyzes this insertion reaction is called an integrase rather than a transposase. The third type of transposon in Table 5-3 also moves by making a DNA copy of an RNA molecule that is transcribed from it. However, the mechanism involved for these nonretroviral retrotransposons is distinct from that just described in that the RNA molecule is directly involved in the transposition reaction.
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