DNA Sequencing — Development of the Sanger Method

Many serious illnesses are directly related to our genetics. Heart disease and cancer are known to “run in the family” whereas Huntington’s disease and cystic fibrosis come directly from genetic mutations. Knowledge of how these diseases work allows researchers to find new ways of treating and/or preventing them. If it weren’t for our collective understanding of genetics, therapeutics would not exist. However, credit for our modern wisdom can be traced back to the development of DNA sequencing in the 1970s when Frederick Sanger and his colleagues created the method that bears his name — Sanger Sequencing.

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DNA sequencing autoradiograph — coloured. Credit: Michele Studer.

DNA recap

We’ve discussed how Deoxyribonucleic Acid (DNA) serves as the blueprint for synthesizing functional molecules in previous blogs. The makeup is important to this blog, however, so a short explanation is in order. DNA is composed of building blocks called nucleotides. These nucleotides contain a nitrogenous base that classifies them as adenine (A), guanine (G), cytosine (C), or thymine (T). Each nucleotide has a pair that it links with across two strands arranged in a double-helix. The pairs are A-T and G-C. Nucleotides within DNA are divided into groups called genes which are classified by which molecule they are encoded to produce. Genes overlap, so more can be fit using fewer nucleotides — an optimization of the genetic code. In essence, the arrangement of genes allows DNA to function by passing instructions that an organism needs to live, develop, and reproduce.

The Road to Sequencing DNA

After elucidating the double-helix structure of DNA as famously announced by Watson and Crick in 1953, scientists began to focus on developing a reliable method for DNA sequencing — the process of determining the sequential order of nitrogenous bases. It was understood that DNA held instructions for producing molecules, but knowing the sequence was essential to gain a deep understanding of living organisms.

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A DNA double helix prior to replication is shown in the top left of the image. Complementary base pairing of nucleotides are shown — adenine with thymine (blue with green) and guanine with cytosine (red with yellow). Credit: Susan Lockhart.

Technological Advances in Sequencing

Building on the improvements already made to Sanger Sequencing, new methods have developed to produce longer sequences in larger volumes with greater accuracy. These methods, collectively known as Next Generation Sequencing (NGS), focus on sequence by synthesis (SBS) and multiplexing — using several different strand simultaneously. The most efficient SBS approach involves the incorporation of a single fluorescently labeled nucleotide per cycle. The reaction is imaged to determine which color was incorporated by each immobilized template. This technique was developed by Solexa, a company that was later acquired by Illumina. Other techniques like 454 sequencing (by roche), SOLiD platform (by Life Technologies), Polonator, and HeliScope single molecule sequencer were developed, resulting in huge increase of sequence data, advances in genomics, and a decrease in the per base cost of DNA sequencing. Like we’ve seen in most technologies over the last few decades — sequencing today is cheaper, faster, and more accurate than ever.

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Welcome to the Macromoltek blog! We're an Austin-based biotech firm focused on using computers to further the discovery and design of antibodies.

Welcome to the Macromoltek blog! We're an Austin-based biotech firm focused on using computers to further the discovery and design of antibodies.

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