Introduction

Deborah Josko

doi:10.29074/ascls.27.3.170

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Deborah Josko, Ph.D. MLT(ASCP)M, SM⇑
1. Associate Professor and Program Director, Department of Clinical Laboratory Sciences, Medical Laboratory Science Program, Rutgers, The State University of New Jersey – School of Health Related Professions, Scotch Plains, NJ

Address for correspondence: Deborah Josko, Ph.D. MLT(ASCP)M, SM, Associate Professor, Department of Clinical Laboratory Sciences, Medical Laboratory Science Program, Rutgers, The State University of New Jersey – School of Health Related Professions 1776 Raritan Road, Scotch Plains, NJ 07076. (908) 889-2422. daj100{at}shrp.rutgers.edu.

Discuss the history of DNA sequencing.
Describe the components of DNA and DNA synthesis.
Compare and contrast dNTPs and ddNTPs.
List several next generation sequencing platforms.

Extract

In 1953, James Watson and Francis Crick were credited with discovering the structure of the DNA molecule: a three dimensional, double helical complex which dictates the genetic code for all forms of life.¹ Although much controversy exists over this discovery notably that the model Watson and Crick proposed was the compilation of the work of several pioneers before them,² they were awarded the Noble Prize in Physiology or Medicine in 1962 along with Maurice Hugh Frederick Wilkins “for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material.”³

The DNA molecule consists of a sugar (deoxyribose) and phosphate backbone along with four chemical base pairs: adenine (A), thymine (T), cytosine (C), and guanine (G). Each base pair is covalently linked to the sugar phosphate backbone. The double helical structure forms once each base pair links to the complementary base on the corresponding strand of deoxyribonucleic acid (DNA) through hydrogen bonding. Due to the chemical make-up of each base, adenine always binds with thymine while cytosine always binds with guanine. The base, sugar and phosphate together constitute a nucleotide.⁴ A key property of the DNA molecule is that it can replicate itself and synthesize a new copy of DNA from the preexisting strand during cell division.

DNA synthesis requires several components: DNA template; primer; deoxyribonucleotide triphosphates (dNTPs): deoxyadenosine triphosphate (dATP), deoxycytidine triphosphate (dCTP), deoxyguanosine triphosphate (dGTP) and deoxythymidine triphosphate (dTTP); various enzymes; and an energy source to fuel the reaction adenosine triphosphate (ATP).⁵

ABBREVIATIONS: A - adenine; ATP - adenosine triphosphate; C - cytosine; dATP - deoxyadenosine triphosphate; dCTP - deoxycytidine triphosphate; ddNTP - dideoxynucleotide triphosphate; dGTP - deoxyguanosine triphosphate; DNA - deoxyribonucleic acid; dNTP - deoxynucleotide triphosphate; dTTP - deoxythymidine triphosphate; G - guanine; mRNA - messenger ribonucleic acid; NGS – next generation sequencing; OH - hydroxyl; SMRT - single molecule real time; T - thymine.