The Dna Sequence

DNA sequence is a continuity of letters showing the main structure of a real or theoretical DNA molecule, with the ability to carry information. There are just four possible letters - A, C, G and T, representing the four nucleotide subunits of a DNA strand - adenine, cytosine, guanine, thymine bases covalently linked to phospho-backbone. The DNA sequence is a detailed description of the order of the chemical building blocks (A, C, G, T), or bases, in a given stretch of DNA. Typically, DNA sequences are printed next to one another without any gaps, as in for example AATGTCTGCC, going from left to right. A succession of any number of nucleotides containing more than four can be called a DNA sequence. It must be noted though that DNA sequences can also contain 'junk DNA'.

DNA Sequencing

The process designed to obtain a DNA sequence is called DNA sequencing. The determination of exact DNA sequence is both an art and a science requiring a heavy investment in technology, expertise and training. In certain (special) cases, more letters, besides A, T, C, and G are to be found in a sequence. These letters represent uncertainty.

DNA sequencing is a process which reveals the exact order of the bases A, T, C and G in a piece of DNA. The first person to successfully develop a DNA sequencing method was Fred Sanger in 1977 for which he won his second Nobel Prize. There are some key principles that one must know in order to understand the process of dNA sequencing. Most DNA sequencing is done using the chain termination method. This includes the synthesis of new DNA strands on a single stranded template and the random incorporation of chain-terminating nucleotide analogues. The chain termination method produces a set of DNA molecules differing in length by one nucleotide. The last base in each molecule can be identified by way of a unique label. Separation of these DNA molecules according to size places them in the correct order to read off the sequence.

During the process of DNA sequencing, laser detection is used to used to identify the bases at each position. The sequence is "read" from the bottom up, using a key where "A" is green, "C" is blue, "G" is yellow, and "T" is red.

Advancements in DNA sequencing technology are set to continue as there is still a lot of room for improvement. The goal is to increase read length and accuracy, increase throughput and decrease the cost.

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