I think there is some confusion. As Dr. Singh mentions above that the "two major divisions of DNA that are transcribed into RNA are protein-coding sections called exons, and nonprotein-coding sections called introns" is not accurate. When a mRNA is initially transcribed, often called a pre-mRNA, it contains extra information that is not present in the final mature mRNA. This extra information/RNA sequence are the introns. While they may contain information that regulates the transcription of the gene, they do not contain sequences that will be translated into the protein (as Dr. Singh correctly mentions). The exons are the sequences that will remain in the mature mRNA. However, they may contain sequences that are translated into the final protein (as Dr. Singh correctly states) or they may contain sequences that are present before and after the translated region (open reading frame), which represent the 5' and 3' untranslated sequences (UTRs). While the 5' UTR and 3' UTR are not translated, they serve important roles in maintaining the stability of the mRNA, the potential subcellular localization of the mRNA, and the regulation of the mRNA translation. Thus, the exons contain both protein-coding (translated) and non-coding (untranslated) sequences.

Also note that the transcription of all mRNAs begins and ends with an exon and introns are located between exons. Students often think that transcription begins with an intron, which contains the 5' UTR, because it is not translated. The process of removing the introns, splicing, requires specific sequences located at the exon-intron junction at the beginning of an intron and the intro-exon junction at the end of the intron. If an intron was located before the first exon or after the last exon, those spicing recognition sequences would not be entirely present and splicing would be disrupted.

Introns(intervienming sequences) are thougt to be nonfunctional gene earlier and exon codes for the expressiion of functional gene recent research have shown that introns play a pivotal role for example in gene silencing in coding some functional genes still research r going on this aspect sir .

http://en.wikipedia.org/wiki/Noncoding_DNA

Thanks, Ravi and Dhanasekaran.

After last sunday's Encode publication, the definition of non coding region and span has been totally changed.

Exons are the region that carry information for a functional protein (genetic code) while introns are the regions interspersed with exons. Its the transcript of exons that are joined after transcription to generate complete mRNA for a functional protein, after splicing of transcripts of introns.

Non-Coding region of DNA refers to the Region that doesn't code for any protein or doesn't carry genetic code. But this doesn't mean It doesn't have any function. It could be doing some regulatory function in the genome.

But Non-Functional DNA refers to the DNA that doesn't have any kind of function in the genome but is just sticking around. It neither codes for a protein, nor does perform any regulatory role. It refers to the "real Junk" But there are a few notions about evolutionary selection of such material to be present in the genome.

Raghu

I think there is some confusion. As Dr. Singh mentions above that the "two major divisions of DNA that are transcribed into RNA are protein-coding sections called exons, and nonprotein-coding sections called introns" is not accurate. When a mRNA is initially transcribed, often called a pre-mRNA, it contains extra information that is not present in the final mature mRNA. This extra information/RNA sequence are the introns. While they may contain information that regulates the transcription of the gene, they do not contain sequences that will be translated into the protein (as Dr. Singh correctly mentions). The exons are the sequences that will remain in the mature mRNA. However, they may contain sequences that are translated into the final protein (as Dr. Singh correctly states) or they may contain sequences that are present before and after the translated region (open reading frame), which represent the 5' and 3' untranslated sequences (UTRs). While the 5' UTR and 3' UTR are not translated, they serve important roles in maintaining the stability of the mRNA, the potential subcellular localization of the mRNA, and the regulation of the mRNA translation. Thus, the exons contain both protein-coding (translated) and non-coding (untranslated) sequences.

Also note that the transcription of all mRNAs begins and ends with an exon and introns are located between exons. Students often think that transcription begins with an intron, which contains the 5' UTR, because it is not translated. The process of removing the introns, splicing, requires specific sequences located at the exon-intron junction at the beginning of an intron and the intro-exon junction at the end of the intron. If an intron was located before the first exon or after the last exon, those spicing recognition sequences would not be entirely present and splicing would be disrupted.

Thanks a lot to all for your informations.

Dear Navonil, can you explain what changes have occurred in the definition of non coding region in the last Encode publication. Or can you please give us any link to have the access to last Encode publication.

Findings from the ENCODE published in 30 papers recently showed that what were considered to be non-functional regions of the genome actually contain regulatory switches. Hence, they are really not junk DNA!

So, these so-called Junk DNAs are responsible for most of the genetic disorders including cancer. These bunch of DNA could be the gate way of new research. May be some epigenetic factors are also responsible for the functioning of these Junk DNA.

Yes Imaran, this is a really new paradigm shift which open wide many opportunities for research work. Have fun while engaging in such fruitful opportunities.

Purist definitions to follow (with spelling errors).

All are parts of a transcript. The introns are spliced out and not transcribed. The Exons and non-coding regions then remain. The exons are transcribed. The start signals for transcription are at the beginning of the sequence and indicate where transcription should start. The stop sequences for transcription are at the end of the transcribed sequence and indicate where to stop transcription. Start and end sequences are the noncoding sequences of the transcript. There is no such thing as "junk DNA." It all has a function, even if we humans don't know it yet.

Everywhere I wrote "transcribed" it should be translated. I was in the hospital at the time. Sorry.

But, the Annotation: Exon^3UTR. What does it means?

Thanks

Yes, used to be called JUNK DNA but no longer correct. Refer to ENCODE project