If a dna sequence of the template strand (in the 3'–5' direction) reads atg, what would be the corresponding mrna codon (in the 5'–3' direction)?

The corresponding mRNA codon for the DNA template strand sequence 'ATG' (in the 3'–5' direction) would be 'UAC' (in the 5'–3' direction). This is because during transcription, which is the process where information from a gene's DNA sequence is translated into a complementary RNA molecule, RNA polymerase reads the template DNA strand in the 3' to 5' direction and assembles an RNA strand in the 5' to 3' direction. Thymine (T) in DNA is replaced by Uracil (U) in RNA, and the complementary base pairing rules apply: Adenine (A) pairs with Uracil (U), and Cytosine (C) pairs with Guanine (G).

Extra: Transcription is the first step of gene expression, where a particular segment of DNA is copied into RNA (especially mRNA) by the enzyme RNA polymerase. The DNA double helix unwinds and the RNA polymerase uses one of the two strands of DNA as a template to synthesize a single strand of RNA, which is then processed to become messenger RNA (mRNA). This mRNA strand carries the code from the DNA out of the nucleus into the cytoplasm where it can be translated by the ribosome into a specific protein. The conversion from DNA sequence to mRNA sequence involves complementary base pairing:

- Adenine (A) in DNA pairs with Uracil (U) in RNA (since RNA does not contain Thymine). - Cytosine (C) in DNA pairs with Guanine (G) in RNA. - Guanine (G) in DNA pairs with Cytosine (C) in RNA. - Thymine (T) in DNA pairs with Adenine (A) in RNA.

The 'ATG' sequence on the DNA when transcribed into mRNA becomes 'UAC', which is read in the 5' to 3' direction, mirroring the way that RNA polymerase adds nucleotides. Understanding this process is fundamental for grasping how genetic information is transferred from DNA to RNA and then into proteins, which perform essential functions in all living cells.