DNA Sequencing

DNA Sequencing

 

 

 

What is Sequencing?

 

Sequencing is the method to determine biopolymer's primary sequence. Sequencing results in a linear string of symbolic letters which summarize important information of genome by genetic code—A, T, G, C.

 

Why sequencing is important?

 

Sequencing is a process to figure out the order of biopolymer such as DNA nucleotides and bases. As we understand the sentence, not only the sequence of the letters but also grammar and the decoding process are required. Similarly, the genome is more than just string of successive letters. Sequencing the genome is an important process in order to understand the meaning of it. Researchers think that studying genome sequence will be helpful for understanding the work of the gonome—how genes work together to direct and regulate the function of cells such as growth, differentiation and maintenance. Finally, portion of genes account for less than 25 percent of the entire genome. Therefore, figuring out the entire genome sequence will be helpful to study the rest parts of the genome except the genes. This region contains the regulatory regions that control gene expression, as well as long stretches of junk DNA— region of genome with unknown function.

 

How sequencing is operated?

 

It's almost impossible to sequence whole genome at once since existing DNA sequencing methods are limited in handling short-stratches at a time. As a result, researchers break down the genome into small fragments and reasseble these fragments into order of original long string. The process of transition of fragmented reads into a long and continuous sequence is assembly. Assembly or alignment takes more time than the sequencing.

 

Which kinds of sequencing techniques are available?

 

“Illumina” licensed sequencing technology using nanopores from Oxford Nanopore Technologies. For sequencing determination, Illumina sequencing system use reversible terminators. Single molecules of DNA are attached to a flat support material, amplified in situ and used as templates for synthetic sequencing with fluorescent reversible terminator deoxyribonucleotides. Another possible way to sequence is by using fluorophore technology. "Pacific Biosciences" is currently SMRT (Single Molecule Real Time) DNA sequencing technology. SMRT sequencing is a harnesses the natural process of DNA replication and can real-time observation of DNA replication by using phosphorlinked deoxyribonucleotides.

 

References

 

1. https://en.wikipedia.org/wiki/Sequencing
2. http://www.genomenewsnetwork.org/resources/whats_a_genome/Chp2_1.shtml
3. N/A. (2008). Accurate Whole Human Genome Sequencing using Reversible Terminator Chemistry. Nature. 456(7218): 53–59.
4. Xiaoge, G., Kevin, L., Karen, O., Jenny Z., Sandeep S. D., & Sue J.R. (2015). SMRT Sequencing for Parallel Analysis of Multiple Targets and Accurate SNP Phasing. G3. g3.115.023317