Suppose that a DNA segment has the following nucleotide sequence:
CTC–ATA–CGA–TTC–AAG–TTA.
Which nucleotide sequences would a complementary mRNA strand have?
(a) GAG–UAU–GAU–AAC–UUG–AAU
(b) GAG–TAT–GCT–AAG–TTC–AAT
(c) GAG–UAU–GCU–AAG–UUC–AAU
(d) GUG–UAU–GGA–UUG–AAC–GGU

Verified step by step guidance

1. Identify the direction of the given DNA sequence and remember that mRNA is synthesized complementary to the DNA template strand, replacing thymine (T) with uracil (U).
2. Recall the base pairing rules for transcription: DNA adenine (A) pairs with RNA uracil (U), DNA thymine (T) pairs with RNA adenine (A), DNA cytosine (C) pairs with RNA guanine (G), and DNA guanine (G) pairs with RNA cytosine (C).
3. Write down the complementary RNA sequence for each DNA triplet by applying the base pairing rules, converting each DNA nucleotide to its RNA complement.
4. Group the resulting RNA nucleotides into codons (triplets) to match the format of the options given.
5. Compare your transcribed mRNA sequence with the provided options to determine which one correctly represents the complementary mRNA strand.

Key Concepts

DNA and RNA Base Pairing Rules

DNA and RNA strands pair through complementary bases: in DNA, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). In RNA, uracil (U) replaces thymine, so adenine pairs with uracil. Understanding these rules is essential to transcribe a DNA sequence into its complementary mRNA sequence.

Transcription Process

Transcription is the process where an mRNA strand is synthesized from a DNA template strand. The mRNA sequence is complementary to the DNA template strand and uses uracil instead of thymine. This process is key to converting the given DNA sequence into the correct mRNA sequence.

Directionality of Nucleic Acid Strands

Nucleic acid sequences have directionality, typically written 5' to 3'. During transcription, the mRNA is synthesized antiparallel to the DNA template strand, meaning the 3' to 5' DNA strand is read to produce a 5' to 3' mRNA strand. Recognizing this helps correctly align and transcribe the sequences.