1. what happens to the dna molecule at the beginning of transcription?

2. then one strand of dna serves as a template for?

in the strand that is formed, the base pairing for the nitrogenous bases is…

3. what signals the beginning and end of transcription?

Transcription starts with an enzyme, called helicase, which opens up the DNA molecule (separate the two strands). RNA-primers will then locate a site in the DNA which is the site that codes for a protein. These areas are inbetween a series of bases which tells the RNA-polymerase to start or stop adding bases. RNA-polymerase adds nitrogenous bases in an order, complementary to the template DNA strand, except that the base T is replaced with the base U. 
When the transcription is over, the mRNA strand that was just made is carried out of the nucleous, and it will find a ribosome to which it can bind and create a protein (translation).

Hope this was any help.

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