1. Initiation:
* RNA polymerase binds to the promoter: Transcription starts at a specific region on the DNA called the promoter. This region contains a sequence that signals the RNA polymerase where to bind.
* DNA unwinds: RNA polymerase unwinds the DNA double helix, exposing the bases.
2. Elongation:
* Reading the template strand: RNA polymerase moves along the DNA template strand, reading the sequence of bases.
* Complementary base pairing: As the enzyme reads the template strand, it uses complementary base pairing rules to build a new RNA molecule:
* Adenine (A) in DNA pairs with Uracil (U) in RNA
* Thymine (T) in DNA pairs with Adenine (A) in RNA
* Guanine (G) in DNA pairs with Cytosine (C) in RNA
* Building the RNA molecule: RNA polymerase adds RNA nucleotides one by one to create a chain of RNA that is complementary to the DNA template strand.
3. Termination:
* Reaching a termination signal: RNA polymerase continues moving along the DNA until it reaches a specific sequence called the terminator. This signal tells the polymerase to stop adding nucleotides.
* Release of the RNA molecule: The newly synthesized RNA molecule detaches from the DNA template, and RNA polymerase releases the DNA.
Key Points:
* Only one DNA strand is transcribed: The DNA template strand (also called the non-coding strand) is the one that is read during transcription. The other strand, called the coding strand, is not used as a template.
* RNA is a single-stranded molecule: Unlike DNA, which is double-stranded, RNA is a single-stranded molecule.
In summary: During transcription, DNA is read by RNA polymerase, which uses the template strand to create a complementary RNA molecule. This process involves unwinding the DNA, reading the bases, and building a new RNA chain. The RNA molecule then detaches from the DNA and is ready for the next stage in protein synthesis.
