How is each nucleotide different

Subject tag:. Printer-friendly version. Search form. Subscribe to our YouTube Channel:. Follow SciencePrimer Tweet. Contact SciencePrimer. Langmuir Circulation. Test sensitivity - specificity calculator. How earthquakes show us the inside of the Earth.

Surface currents, the Ekman spiral, and Ekman transport. The primer's sequence is complementary to the first piece of target DNA, which means that the primer and the DNA target bind with each other.

At this point, the target sequence is exposed to a solution that contains DNA polymerase and all of the nucleotides required for synthesis of the complementary DNA strand — along with one special ingredient. As described above, the next major step in the Sanger process is to expose the target sequence to DNA polymerase and significant amounts of all four nucleotides.

In their unbound form, nucleotides have three phosphate groups and are formally called deoxynucleotide triphosphates , or dNTPs where the "N" is a placeholder for A, T, G, or C. During the construction of a new DNA strand, a molecule called a hydroxyl group which contains an oxygen atom and a hydrogen atom attaches to the sugar of the last dNTP in the strand and chemically binds to the phosphate group on the next dNTP.

This binding causes the DNA chain to grow. In Sanger sequencing, however, a special type of "dummy" nucleotide is included with the regular dNTPs that surround the growing DNA strand.

These special nucleotides are known as dideoxynucleotide triphosphates , or ddNTPs Figure 2 , and they lack the crucial hydroxyl group that is attached to the sugar of dNTPs. When Sanger sequencing was first introduced, four separate reagents were used, one for each type of ddNTP.

The four reaction products were then separated by gel electrophoresis, a process that organizes DNA fragments in order of size. This enabled researchers to assess the lengths of the truncated strands in each sample. This was important, because the end of each truncated strand was used to determine the position at which a ddNTP was added to the strand, thereby halting DNA elongation.

This page appears in the following eBook. Aa Aa Aa. How do researchers "read" gene sequences? Determining the order of the nucleotides within a gene is known as DNA sequencing. The earliest DNA sequencing methods were time consuming, but a major breakthrough came in with the development of the process called Sanger sequencing. Sanger sequencing is named after English biochemist Frederick Sanger, and it is sometimes also referred to as chain-termination sequencing or dideoxy sequencing.

Some 25 years after its creation, the Sanger method was used to sequence the human genome, and, with the addition of many technological improvements and modifications, it remains an important method in laboratories across the world today. How does Sanger sequencing work? Understanding DNA replication. Setting up the sequencing experiment. Adding ddNTPs. Figure 2: The four ddNTPs. Figure 3: By adding together information about all of the truncated strands, researchers can determine the nucleotide sequence of the DNA target.

The sugar-phosphate backbone is depicted as gray, horizontal cylinders stacked end-to-end. Each cylinder is attached to a thin rectangle, representing the nucleotide. Gray nucleotides have an unknown chemical composition. Green nucleotides represent adenine, and orange nucleotides represent cytosine. The sequence of nucleotides is: two gray, green, orange, gray, orange, two gray, green, 5 gray, green, gray.

In the bottom DNA strand, eight nucleotides are base paired with the upper strand on the right side. The second sugar-phosphate group is colored black instead of gray, indicating that it contains a dideoxy-ribose sugar, and the first nucleotide is off-set to indicate that it is not bound to the DNA chain. The sequence of the paired nucleotides is: red thymine , blue guanine , orange, blue, green, orange, red, blue.

Figure 9: Supercoiled eukaryotic DNA. How do scientists visualize DNA? Figure This karyotype depicts all 23 pairs of chromosomes in a human cell, including the sex-determining X and Y chromosomes that together make up the twenty-third set lower right.

Watch this video for a closer look at the relationship between chromosomes and the DNA double helix. What are karyotypes used for? Who is James Watson? What do we know about Francis Crick? Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics. Student Voices. Creature Cast.

Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Postcards from the Universe. Brain Metrics. Mind Read. Eyes on Environment. Accumulating Glitches. Saltwater Science. Microbe Matters.

You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session? This article has been posted to your Facebook page via Scitable LearnCast. Change LearnCast Settings. Scitable Chat. Register Sign In.