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Strand

A DNA molecule consists of two strands of nucleotides. Each nucleotide is one of the four molecules adenine, guanine, thymine, or cytosine. Adenine always pairs with guanine and thymine always pairs with cytosine. A pair of matched nucleotides is called a base pair, and DNA lengths are often described in terms of a number of bases (e.g. 100 kilobases for 100,000 base pairs).

Name Letter Type Pairs With Formula
adenine a pyrmidine thymine C5H5N5
guanine g purine cytosine C5H5N5O
cytosine c purine guanine C4H5N3O
thymine t pyrimidine adenine C5H6N2O2
DNA.gif
For each contiguous sequence of DNA, only one sequence of letters is stored in the Sprout Database. Each such sequence, however, corresponds to two different DNA sequences. The first is the sequence as it appears in the database, and is known as the plus strand. The second is the sequence on the other side of the DNA molecule proceeding in the opposite direction. This is called the minus strand or reverse complement.


StrandLetters.png
The image to the left illustrates this principle. The plus strand is shown in blue. The corresponding nucleotides on the minus strand are shown in green. When this section of the DNA is being used to build proteins via the plus strand, the protein sequence is SFIVGTRF. When the minus strand is being used, the complementary codes are read in reverse order. The protein sequence in this case is KSCSNYER.


Further reading:

Topic revision: r3 - 16 Jan 2009 - 15:14:05 - Bruce Parrello
 
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