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How to Calculate Reverse Complements

DNA is a double-stranded molecule in which each strand runs counter to the other (anti-parallel). DNA, and RNA, consist of repeating units called nucleotides, each of which are composed of a sugar, a phosphate and a nitrogenous base. Nucleotides are of two types---purines and pyrimidines---that will form hydrogen bonds between their nitrogenous bases in a particular, complementary fashion. Per Chargaff's Rule, the purine adenine (A) will only pair with the pyrimidine thymine (T), and the purine guanine (G) will only pair with the pyrimidine cytosine (C). Calculating the reverse complement of a DNA sequence is simply figuring out what the complementary strand is and placing it in the 5'-3' direction. Calculate the reverse complement of a nucleic acid sequence in either of two ways.

Instructions

- 1
  Take your sequence in question (for example: 5' -- G G A C C C C C G G G T -- 3') and determine the complement for each base in order: 3' -- C C T G G G G G C C C A -- 5'. (This complementary strand is in the anti-parallel orientation, as indicated by the 3'-5' direction.)
- 2
  Write the new strand backwards, beginning with the 5' end: 5' -- A C C C G G G G G T C C -- 3'. This is the reverse complement of the original sequence.
- 3
  Alternatively, take the sequence of interest and turn it around first. For the same sequence from above (5' -- G G A C C C C C G G G T -- 3') reverse the sequence to get: 3' -- T G G G C C C C C A G G -- 5'
- 4
  Write the complement for each nucleotide in order. This is now the same complementary strand in reverse orientation that you reached in Step 2: 5' -- A C C C G G G G G T C C -- 3'.

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