What makes a strand of dna

DNA's instructions are used to make proteins in a two-step process. First, enzymes read the information in a DNA molecule and transcribe it into an intermediary molecule called messenger ribonucleic acid, or mRNA. Next, the information contained in the mRNA molecule is translated into the "language" of amino acids, which are the building blocks of proteins. This language tells the cell's protein-making machinery the precise order in which to link the amino acids to produce a specific protein.

This is a major task because there are 20 types of amino acids, which can be placed in many different orders to form a wide variety of proteins. But nearly a century passed from that discovery until researchers unraveled the structure of the DNA molecule and realized its central importance to biology. For many years, scientists debated which molecule carried life's biological instructions. Most thought that DNA was too simple a molecule to play such a critical role.

Instead, they argued that proteins were more likely to carry out this vital function because of their greater complexity and wider variety of forms. By studying X-ray diffraction patterns and building models, the scientists figured out the double helix structure of DNA - a structure that enables it to carry biological information from one generation to the next. Despite his scientific achievements, Dr. Scientist use the term "double helix" to describe DNA's winding, two-stranded chemical structure.

This shape - which looks much like a twisted ladder - gives DNA the power to pass along biological instructions with great precision. To understand DNA's double helix from a chemical standpoint, picture the sides of the ladder as strands of alternating sugar and phosphate groups - strands that run in opposite directions. Each "rung" of the ladder is made up of two nitrogen bases, paired together by hydrogen bonds. Because of the highly specific nature of this type of chemical pairing, base A always pairs with base T, and likewise C with G.

So, if you know the sequence of the bases on one strand of a DNA double helix, it is a simple matter to figure out the sequence of bases on the other strand. DNA's unique structure enables the molecule to copy itself during cell division.

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. What is DNA? From Genetics Home Reference. DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone. What is a gene? What is a chromosome? 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. In a smaller diagram to the left of the larger chain, examples of resulting truncated nucleotide chains help decipher the DNA sequence. Under the heading ddTTP, three nucleotide chains are shown. The first chain contains 14 nucleotides, with a red ddTTP inserted in the left-most position, truncating synthesis.

The second chain contains 8 nucleotides, also truncated with a ddTTP. The third chain contains only 2 nucleotides, truncated after ddTTP addition. Under the heading ddGTP, two nucleotide chains are shown. The first chain contains 13 nucleotides, truncated after ddGTP addition. The second chain contains 11 nucleotides, also truncated after ddGTP addition.

After complete analysis with all four ddNTPs, the final nucleotide sequence is shown in the right panel. Nucleotides are represented by different colored rectangles: red for thymine, blue for guanine, green for adenine, and orange for cytosine. Below the sequenced strand, examples of truncated strands from the four reactions are shown. Reading the sequence: Now and then. How is DNA sequencing used by scientists? In recent years, DNA sequencing technology has advanced many areas of science.

For example, the field of functional genomics is concerned with figuring out what certain DNA sequences do, as well as which pieces of DNA code for proteins and which have important regulatory functions.

An invaluable first step in making these determinations is learning the nucleotide sequences of the DNA segments under study. Another area of science that relies heavily on DNA sequencing is comparative genomics, in which researchers compare the genetic material of different organisms in order to learn about their evolutionary history and degree of relatedness.

DNA sequencing has also aided complex disease research by allowing scientists to catalogue certain genetic variations between individuals that may influence their susceptibility to different conditions.

How can all people benefit from DNA sequencing? More about sequencing.