Describe the effects of transposons and retrotransposons
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wat are transpoons even i need to know it
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DNA Transposons
Most DNA transposons, sometimes referred to as Class II mobile genetic elements, actually use two enzymes, transposase and integrase, to move from one location in the genome to another; they are literally “cut" out of their location and “pasted" into a new one. This type of transposition does not involve RNA. The enzymes may recognize specific sequences for insertion, though many types of enzyme can actually bind to virtually any sequence, allowing the element to be inserted anywhere. At the site where the transposon is to be inserted, the DNA is cut in what’s called a “staggered" manner to create “sticky ends"; what this means is that nucleotides are left without corresponding paired bases. Once the transposon is inserted into the target site, a DNA polymerase adds the missing nucleotides. This filling in of the gaps leads to duplication of short DNA sequences flanking the transposon and this has been hypothesized as a mechanism behind gene duplication. Finally, some DNA transposons actually will replicate themselves, with the copy then being inserted into the target site.
Just as occurs with retrotransposons, there have been cases observed in which DNA transposable elements have lost the enzymes necessary for transposition. They continue to be able to move thanks to the presence of enzymes encoded by other mobile elements. Besides the enzymes important for transposition, some bacterial transposons actually carry genes that are unrelated to movement and that confer an advantage; these are the genes responsible for the rapid spread of antibiotic resistance among bacteria.
Are Transposons Good or Bad?
The movement of transposable elements can actually impact the phenotype of an organism and the amount of DNA in its genome. The replication of sequences to be inserted into new locations, as well as the filling in of gaps created by transposition, often increase the amount of genetic information in a genome.
On phenotypes, there can be multiple effects:
If transposons insert themselves into a coding region or into a regulatory sequence, they will most probably render that gene inactive.
Upon leaving a site, the gap that is left by a transposon will need to be repaired; this repair, often, will cause genetic mutations in the original gene and render it inactive.
Sequences that are repeated multiple times lead to unequal crossing over and chromosomal abnormalities.
A number of diseases in the human genome have been linked to transposons, such as Hemophilia A and B, Severe Combined Immunodeficiency, Porphyria, predisposition to cancer, and Duchenne Muscular Dystrophy.
Despite these negative aspects, there can be positive impacts of transposable elements:
Sometimes non-transposon, coding, DNA gets carried along with mobile elements during transposition; this could lead to the duplication of beneficial genes or the creation of new genes.
Sometimes genetic mutations caused by transposons may modify regulatory sequences and this could change the pattern of expression of a gene or its timing or the amount of gene produced, which could lead to some new, beneficial characteristics.
The rate of transposition has actually been observed to increase in some cases under conditions of stress. This higher rate of transposition could cause genetic mutations leading to new traits, which would allow an organism to better adapt to changing environmental conditions.
Transposons have also come in handy as tools for scientists who wish to create transgenic organisms or modify an organism’s DNA for research purposes.
DNA Transposons
Most DNA transposons, sometimes referred to as Class II mobile genetic elements, actually use two enzymes, transposase and integrase, to move from one location in the genome to another; they are literally “cut" out of their location and “pasted" into a new one. This type of transposition does not involve RNA. The enzymes may recognize specific sequences for insertion, though many types of enzyme can actually bind to virtually any sequence, allowing the element to be inserted anywhere. At the site where the transposon is to be inserted, the DNA is cut in what’s called a “staggered" manner to create “sticky ends"; what this means is that nucleotides are left without corresponding paired bases. Once the transposon is inserted into the target site, a DNA polymerase adds the missing nucleotides. This filling in of the gaps leads to duplication of short DNA sequences flanking the transposon and this has been hypothesized as a mechanism behind gene duplication. Finally, some DNA transposons actually will replicate themselves, with the copy then being inserted into the target site.
Just as occurs with retrotransposons, there have been cases observed in which DNA transposable elements have lost the enzymes necessary for transposition. They continue to be able to move thanks to the presence of enzymes encoded by other mobile elements. Besides the enzymes important for transposition, some bacterial transposons actually carry genes that are unrelated to movement and that confer an advantage; these are the genes responsible for the rapid spread of antibiotic resistance among bacteria.
Are Transposons Good or Bad?
The movement of transposable elements can actually impact the phenotype of an organism and the amount of DNA in its genome. The replication of sequences to be inserted into new locations, as well as the filling in of gaps created by transposition, often increase the amount of genetic information in a genome.
On phenotypes, there can be multiple effects:
If transposons insert themselves into a coding region or into a regulatory sequence, they will most probably render that gene inactive.
Upon leaving a site, the gap that is left by a transposon will need to be repaired; this repair, often, will cause genetic mutations in the original gene and render it inactive.
Sequences that are repeated multiple times lead to unequal crossing over and chromosomal abnormalities.
A number of diseases in the human genome have been linked to transposons, such as Hemophilia A and B, Severe Combined Immunodeficiency, Porphyria, predisposition to cancer, and Duchenne Muscular Dystrophy.
Despite these negative aspects, there can be positive impacts of transposable elements:
Sometimes non-transposon, coding, DNA gets carried along with mobile elements during transposition; this could lead to the duplication of beneficial genes or the creation of new genes.
Sometimes genetic mutations caused by transposons may modify regulatory sequences and this could change the pattern of expression of a gene or its timing or the amount of gene produced, which could lead to some new, beneficial characteristics.
The rate of transposition has actually been observed to increase in some cases under conditions of stress. This higher rate of transposition could cause genetic mutations leading to new traits, which would allow an organism to better adapt to changing environmental conditions.
Transposons have also come in handy as tools for scientists who wish to create transgenic organisms or modify an organism’s DNA for research purposes.
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