Transcription steps

Step 1

RNA Polymerase binds to the promoter

RNA Polymerase binds to a region on the DNA called the promoter. This is the start signal that tells it where to begin.

Why: the cell needs to know which gene to copy — the promoter marks the right place.

Step 2

The DNA unwinds and unzips

RNA Polymerase unwinds the DNA double helix and breaks the hydrogen bonds between the base pairs. This exposes the template strand.

Why: the template strand is what gets read — it can't be read while it's zipped up.

Step 3

mRNA is built

RNA Polymerase reads the template strand and builds a complementary mRNA strand. It follows base pairing rules — A pairs with U, C pairs with G. U is used instead of T because mRNA is RNA, not DNA.

Why: this is the actual copy being made — the mRNA is the message that will be sent out.

Step 4

RNA Polymerase stops and detaches

RNA Polymerase reaches the terminator sequence — the stop signal. It detaches from the DNA and releases the mRNA strand. The DNA double helix reforms — zips back up.

Why: the gene has been fully copied so the process ends here.

Step 5

mRNA is processed and leaves the nucleus

The mRNA is processed — a 5' cap and poly-A tail are added to protect it, and non-coding sections called introns are removed. The remaining sections (exons) are joined together. The mature mRNA exits the nucleus through nuclear pores and travels to the ribosome.

Why: the mRNA needs to be ready and protected before it can be used to make