Junk Dn Dna Rna And Transcription Of Genes - 1966 Words

Junk DNA Hengye Chen 813198898 Background: When scientists sequenced genome at early period, they found that only a small part of genomic DNA sequence can code proteins. Major DNA sequence did not have function. Then they named those DNA sequences that could not code for proteins as â€Å"Junk DNA†. However, after researching for decades, many sequences thought were useless in that time now have identified functions, such as many regulatory elements, DNA sequences coded for noncoding RNA, origins of DNA replication and so on. Thus, the definition of â€Å"Junk DNA† also need to be change during these discoveries. In my mind, now â€Å"Junk DNA† is a term used to represent those noncoding DNA sequences that have undiscovered function or do not have†¦show more content†¦Telomeres are terminal sequences of genomic DNA. They are important for the stability of chromosomes. Centromeres are sequences located in centers of chromosomes. They are important for chromosome stability and cell division. Transposons are DNA sequences that can translocate from one site of a chromosome to another site of a chromosome. Most of them are silenced in normal mammal cells .There are two classes of transposons. Class I is retrotransposon and Class II is DNA transposon. There are three types of retrotransposons in Class I and one in Class II. So normally, transposable elements can be categorized in four types. In addition, transposons can be classed into two type, autonomous and non-autonomous, with a different method (Figure 1) [1]. Retrotransposon is a major component of â€Å"Junk DNA†. It can copy itself and it contains long terminal repeat (LTR) transposons (retrovirus-like), long interspersed nuclear elements (LINEs) and short interspersed nuclear elements (SINEs) which occupy a huge part of the genome [1]. LTR transposons are transposons flanked by long terminal repeats. This character is similar to retrovirus. There are two types of LTR transposons. One is autonomous transposon which contains gag, pol and envelop genes. It can code all enzyme needed for reverse transcription in a retroviral manner, and then induces integration and causes amplification of sequences. The other one is