Final answer:
During elongation in transcription, RNA polymerase synthesizes mRNA in the 5' to 3' direction by reading the template DNA strand and adding nucleotides at a rate of about 40 nucleotides per second. The DNA is unwound in front of the enzyme and rewound behind it as the process continues.
Step-by-step explanation:
During the transcription phase known as elongation, an enzyme called RNA polymerase is responsible for synthesizing messenger RNA (mRNA). RNA polymerase reads the template DNA strand and adds RNA nucleotides to the growing mRNA strand in the 5' to 3' direction. This means that the nucleotides are added to the 3' end of the mRNA. As this process unfolds, the DNA is continuously unwound ahead of the polymerase and rewound behind it, enabling the RNA polymerase to track along the DNA and synthesize mRNA.
The elongation process is characterized by the pairing of incoming RNA nucleotides with the complementary bases on the DNA template strand. It is crucial to note that during this pairing, uracil (U) is incorporated into the RNA strand in place of thymine (T), which is found in DNA. The rate of nucleotide addition in elongation is approximately 40 nucleotides per second, and the growing mRNA strand detaches from the DNA, as it is not meant to remain bound to the template.