AP BIOLOGY

Detailed explanation-1: -Once transcription is initiated, the DNA double helix unwinds and RNA polymerase reads the template strand, adding nucleotides to the 3′ end of the growing chain (Figure 2b).

Detailed explanation-2: -The main enzyme involved in transcription is RNA polymerase, which uses a single-stranded DNA template to synthesize a complementary strand of RNA. Specifically, RNA polymerase builds an RNA strand in the 5’ to 3’ direction, adding each new nucleotide to the 3’ end of the strand.

Detailed explanation-3: -RNA polymerase always builds a new RNA strand in the 5’ to 3’ direction. That is, it can only add RNA nucleotides (A, U, C, or G) to the 3’ end of the strand.

Detailed explanation-4: -Then, a sequence of adenine nucleotides called a poly-A tail is added to the 3’ end of the mRNA molecule (Figure 7). This sequence signals to the cell that the mRNA molecule is ready to leave the nucleus and enter the cytoplasm.

Detailed explanation-5: -Once elongation is complete, another processing enzyme then adds a string of approximately 200 adenine nucleotides to the 3’ end, called the poly-A tail.