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Difference between EST and cDNA? - (Jan/06/2012 )

Hi all,

I am not in molecular biology field, but I need to understand more about EST(expressed sequence tags). I am wondering how is it generated? Is it from mRNA? After reading info in Wiki, I think cDNA is generated from mRNA as well. So what is the difference of the two? I am really confused about these two. It seems that some mature peptides are in cDNA but not in EST yet. Any explanations? Thank you very much.



I am wondering how is it generated?
ESTs are generated by sequencing cDNA, which itself is synthesized from the mRNA molecules in a cell

So what is the difference of the two?
EST's are small sequences generated from sequencing cDNA, but only a small portion, this can be used as a sign to identify the gene and does not reveal the whole gene sequence as cDNA does


so cDNA sequence is obtained by sequencing of the real sample. But how can you know which part of cDNA is EST? Is EST based on prediction? Or people can get this each small portion from sample prep?


EST is a type of cDNA, resulted from single pass sequencing of a (full-length) cDNA clone. Because it is single pass read and sequencing reaction could only reach about 500 bp, so ESTs are short sequences. Most ESTs are from the 3' end of a full-length cDNA sequence because early cDNA sequencing was from the 3 end of polyA tailed mRNA. Later new methods of single pass sequencing cDNA from the 5' end or middle of a cDNA were used, so some ESTs are also from 5' end or middle of a gene. From sequencing millions of ESTs in a single sample, one is able to know the expression of every gene by counting the number of ESTs representing each gene.


So does it mean the sequence of the cDNA is actually obtained by sequecing each EST and then put together? So if a peptide-encoding DNA is in the cDNA, then it must have a EST acession number as well?