Elongation

Term from genetics. Elongation refers to the phase of transcription in which the RNA polymerase elongates the RNA chain by adding nucleotides to a growing RNA molecular chain. This phase follows initiation, in which the RNA polymerase binds to the promoter of the DNA and establishes the transcription start point.

RNA polymerase binding: After initiation, the RNA polymerase remains bound to the DNA. The DNA double strand is opened locally so that the template strand (the strand that serves as a template for RNA synthesis) is accessible.

Nucleotide incorporation: The RNA polymerase begins to add RNA nucleotides. The RNA is synthesized in the 5'-to-3' direction, which means that the RNA polymerase adds nucleotides to the 3' end of the growing RNA strand. The nucleotides that are incorporated into the RNA are based on the complementary sequence of the DNA:

- Adenine (A) in the DNA pairs with uracil (U) in the RNA.

- Thymine (T) in the DNA pairs with adenine (A) in the RNA.

- Cytosine (C) in the DNA pairs with guanine (G) in the RNA.

- Guanine (G) in the DNA pairs with cytosine (C) in the RNA.

Catalyzing the phosphodiester bond: At each step of RNA synthesis, RNA polymerase catalyzes the formation of a phosphodiester bond between the 3'-OH end of the growing RNA strand and the 5'-phosphate of the incoming nucleotide. This process releases energy derived from the hydrolysis of the NTPs (nucleoside triphosphates).

Movement along the DNA: During elongation, the RNA polymerase moves along the DNA strand, closing the DNA double helix as it moves further away from the transcription site.