A portion of a DNA template strand has the base sequence 5′-...ACGCGATGCGTGATGTATAGAGCT...-3′

Identify the sequence and polarity of the mRNA transcribed from this fragmentary template-strand sequence.

Key Concepts

Transcription

Transcription is the process by which the genetic information encoded in DNA is copied into messenger RNA (mRNA). During transcription, RNA polymerase binds to the DNA template strand and synthesizes a complementary RNA strand. The RNA is synthesized in the 5' to 3' direction, meaning that the RNA strand will have a polarity opposite to that of the DNA template strand.

Base Pairing Rules

Base pairing rules dictate how nucleotides pair during the transcription process. In RNA, adenine (A) pairs with uracil (U) instead of thymine (T), which is found in DNA. Therefore, when transcribing a DNA sequence, cytosine (C) pairs with guanine (G), guanine (G) pairs with cytosine (C), adenine (A) pairs with uracil (U), and thymine (T) pairs with adenine (A).

Polarity of Nucleic Acids

Nucleic acids, including DNA and RNA, have directionality or polarity, indicated by the 5' and 3' ends. The 5' end has a phosphate group, while the 3' end has a hydroxyl group. This polarity is crucial during transcription, as RNA polymerase adds nucleotides to the 3' end of the growing mRNA strand, resulting in an mRNA molecule that is complementary to the DNA template strand and has a 5' to 3' orientation.