Complementing a Strand of DNA

25 Oct 2023 in Study / Rosalind on Rosalind problem

A problem from rosalind “Bioinformatics Stronghold” category, String Algorithm

• A problem from rosalind “Bioinformatics Stronghold” category
  Rosalind Problem Link

• Description
  • Given DNA sequence, we should deduce the reverse complement
• Input example : AGGCCTTAGGCAGT
• Output example : ACTGCCTAAGGCCT

Biological Background

• DNA consists of 2 strands
  • coding sequence : has same sequences with mRNA having information except T (should be changed to U)
  • noncoding sequence : complement version of coding sequence (A ↔ T, G ↔ C)
• 2 strands are antiparellel
  • 5’-AGGCT-3’
  • 3’-TCCGA-5’
  • Reverse complement of 5’-AGGCT-3’ is 5’-AGCCT-3’

My Solution

DNA_seq = input()
reverse_c = ""

for i in range(len(DNA_seq) - 1, -1, -1):
    symbol = DNA_seq[i]
    newSymbol = ''

    if symbol == 'A':
        newSymbol = 'T'
    elif symbol == 'T':
        newSymbol = 'A'
    elif symbol == 'G':
        newSymbol = 'C'
    elif symbol == 'C':
        newSymbol = 'G'
    reverse_c += newSymbol

print(reverse_c)

• Search by the reverse direction on suggested DNA sequence
• add the complement symbol into reverse_c