Which strand of the DNA is sequenced ? Is one of the strands completely "coding" or completely "template" ?

Question

[karakasmenderes6]

As I said in the title I wonder Which strand of the DNA is sequenced? Is one of the strands completely "coding" or completely "template"? In college (I will be in my second year in college) they only taught us the central dogma, how transcription and translation occur. Actually they also mention the template and coding strands. After I try to learn bioinformatics I started to think about those because as you know people sequence whole genomes and sometimes I try to find an mRNA sequence in the whole genome but I couldn't be sure because if the sequenced strand coding or not as you know mRNA is the same as the coding strand. I also don't know if they sequence both of the strands and in fasta files, only contain protein coding regions or by nature, only one strand is coding strand.

Thanks in advance :)

Answer 1

[GenoMax]

In general DNA sequencing either strand of DNA has an equal chance of getting sequenced. It is because of how libraries (fragmentation of genomic DNA followed by attachment of oligo adapters which allows binding to a substrate) are made. Since sequencing always proceeds in 5' --> 3' direction that is the sequence you see. Thus concept of top/bottom strand is in somewhat artificial. There are directional sequencing methods in transcriptomic sequencing that sequence a specific strand to determine which strand of DNA is being transcribed (see: A: Ht-Seq Read Count And Strand-Specificity for a visual explanation).

[karakasmenderes6]

Thanks a lot for the answer

[jonas.andersson]

I still don't understand this completely yet. Let's say you do a WGS, how do you know which sequences in your data that are originating from the coding strand and will eventually become proteins? I'm confused...