Final answer:
The synthesis of mRNA occurs in theC. 5' to 3' direction with new nucleotides being added to the 3' end. The process involves 5' capping and the addition of a 3' poly-A tail, after which the mature mRNA moves to the cytoplasm for protein synthesis.
Step-by-step explanation:
The synthesis of mRNA occurs in the 5' to 3' direction with new nucleotides being added to the 3' end of the mRNA molecule. The process starts with the unwinding of the gene portion of the DNA to form a transcription bubble. RNA polymerase catalyzes mRNA synthesis by moving along the DNA template strand in a 3' to 5' direction, assembling the mRNA in a 5' to 3' direction. As the RNA polymerase reads the template strand, where adenine (A) pairs with uracil (U) and cytosine (C) pairs with guanine (G), the new mRNA strand grows with complementary nucleotides.
During the synthesis, additional processes occur, such as 5' capping and the addition of a 3' poly-A tail. The 5' cap is a 7-methylguanosine cap added to the 5' end of the growing transcript, providing protective and initiation functions for translation. The 3' end is cleaved near an AAUAAA sequence after which the poly-A tail is added, protecting the pre-mRNA from degradation. The mature mRNA then exits the nucleus to the cytoplasm for translation into proteins.