When you change the dna code to mRNA, will A become U or T?
When we change the DNA code to messenger RNA (mRNA), the base adenine (A) in the DNA sequence will become uracil (U) in the mRNA sequence.
To determine this, you need to understand the complimentary base pairing rules between DNA and RNA. In DNA, adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). However, in RNA, adenine (A) pairs with uracil (U) instead of thymine (T), while cytosine (C) still pairs with guanine (G).
So, during transcription (the process of creating mRNA from DNA), when the DNA strand gets transcribed, each adenine (A) base in the DNA sequence will be complemented with a uracil (U) base in the resulting mRNA sequence. The rest of the bases (cytosine, guanine, and thymine) remain the same.
Keep in mind that this rule only applies to the transcription process, where DNA is converted into mRNA. In DNA replication or DNA synthesis, adenine (A) would still pair with thymine (T).