Transposons are mobile pieces of DNA that can cause mutations and change the amount of DNA within a cell. They are grouped into two categories: class II transposons and class I transposons or retrotransposons, which move through a two-step process involving RNA and reverse transcriptase. Retrotransposons usually have long terminal repeats (LTRs) and can increase the amount of DNA in a cell, potentially causing mutations. About 42% of the human genome is made up of retrotransposons.
Transposons are pieces of DNA that are mobile or can move to different places within the genetic information of a cell. By moving to a new location within a cell’s genome, transposons can cause mutations and change the amount of DNA found within the cell. They are also referred to as skipping genes and are grouped into two categories which are class II transposons and class I transposons or retrotransposons. The difference between these two classes has to do with how they move; a retrotransposon has a two-step movement process.
The method of DNA segment movement is how transposons are classified in each category. A class II transposon is a piece of DNA that moves from one place to another. The movement of a class I transposon, or retrotransposon, is much more complex and involves two steps for the movement of the DNA segment.
The first step in the movement of a retrotransposon is to create a segment of RNA by transcribing a piece of DNA. The RNA is now free to move through the genome as it is not bound to a DNA strand. When the RNA reaches its new location, a specific enzyme called reverse transcriptase creates a new DNA strand based on the RNA segment. This new piece of DNA is then attached to the new location within the genome.
When a retrotransposon is transcribed into a segment of DNA from the RNA copy, it usually has long terminal repeats (LTRs) at the end of the DNA sequence. LTRs consist of repeating sequences of bases that can be hundreds or even thousands of bases long. They usually surround a functional part of DNA, such as a gene, and are needed to attach the DNA segment to the original DNA strand. LTRs are one way scientists can recognize that a section of DNA contains a retrotransposon. About 42% of the entire human genome is thought to consist of retrotransposons.
Due to the fact that new copies of DNA are made through reverse transcription of RNA, adding a retrotransposon is one way to increase the amount of DNA found within a single cell. If a retrotransposon is inserted into or near a gene, it can cause a mutation. Mutations are basically changes in the DNA sequence and can have a positive, negative or no impact on the genome, depending on how the DNA sequence is altered.
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