Final answer:
The mRNA sequence is complementary to the DNA template strand, with adenine pairing with uracil instead of thymine. Eukaryotic mRNA may be modified after transcription, resulting in a molecule that is shorter than the DNA sequence it was transcribed from due to intron removal.
Step-by-step explanation:
The mRNA contains a sequence that is complementary to the template strand of the original DNA. During the transcription process, when an mRNA strand is synthesized from DNA, uracil (U) is used in place of thymine (T). Therefore, adenine (A) pairs with uracil (U) in mRNA, instead of thymine (T), and cytosine (C) pairs with guanine (G), as in DNA. If the DNA strand has a sequence of 3'......GCT GTC AAA TTC GAT......5', the complementary mRNA sequence would be 5'......CGA CAG UUU AAG CUA......3'. This mRNA sequence is then translated into a chain of amino acids in the ribosome, forming a protein.
However, in eukaryotic cells, the mRNA molecule can undergo modifications after it is transcribed and before it leaves the nucleus. These modifications can include the addition of a 5' methylguanosine cap and a 3' poly-A tail, as well as the splicing of introns out of the pre-mRNA. This splicing can result in an mRNA molecule that is considerably shorter than the DNA sequence from which it was transcribed due to the removal of non-coding regions.