old_contents: # Use the codon variables you defined previously
  S = "TCT"
  L = "CTT"
  Y = "TAT"
  C = "TGT"
  
  # Create a list for the protein sequence CLYSY
  codons = [C, L, Y, S, Y]
  
  # Print the DNA sequence of the protein
  print("DNA sequence:", codons)
  
  # Print the DNA sequence of the last amino acid
  print("Last codon:", codons[-1])
  
  # Create two more variables containing the DNA sequence for a stop codon and a start codon
  start = "ATG"
  stop = "TGA"
  
  # Replace the first element of the list with the start codon
  codons[0] = start
  
  # Append the stop codon to the end of the list
  codons.append(stop)
  
  # Print the resulting DNA sequence
  print("DNA sequence after alteration:", "".join(codons))
  
new_contents: # Use the codon variables you defined previously
  S = "TCT"
  L = "CTT"
  Y = "TAT"
  C = "TGT"
  
  # Create a list for the protein sequence CLYSY
  codons = [C, L, Y, S, Y]
  
  # Print the DNA sequence of the protein
  print("DNA sequence:", codons)
  
  # Print the DNA sequence of the last amino acid
  print("Last codon:", codons[-1])
  
  # Create two more variables containing the DNA sequence for a stop codon and a start codon
  start = "ATG"
  stop = "TGA"
  
  # Replace the first element of the list with the start codon
  codons[0] = start
  
  # Append the stop codon to the end of the list
  codons.append(stop)
  
  # Print the resulting DNA sequence
  print("DNA sequence after alteration:", codons)
  
subject: Remove join in exercise 1.3.1 not seen yet in course