title: transcribe mRNA code from DNA strand
body: <p>I thought it would be easy to replace the string a into u and so on with this code</p>
  
  <pre><code>DNA= "atgcatgctagcagtcagcatcgatcgatcagctagctag"
  
     def transcribe(dna):
  
       dna.replace("a", "u")
       dna.replace("t", "a")
       dna.replace("g", "c")
       dna.replace("c", "g")
       return 
  </code></pre>
  
  <p>it didn't change my variable at all. Can anybody help me to solve this?</p>
  
  <p>Thank you</p>