DNA strands run in 1 of 2 directions depending on which end of the strand is free and which end has a phosphate bond. One direction is 5' to 3' () and the other direction is 3' to 5' (downstream). polymerase binds to the DNA at the TATA box and unzips the double helix. Working along the DNA chain, RNA polymerase reads the DNA nitrogenous bases and matches RNA nitrogenous bases from the nucleus (uracil instead of thymine). As it moves, RNA polymerase re-zips the DNA behind it and lets the mRNA separate from the DNA. It continues to do this until it reaches a sequence downstream called a signal. In other words, RNA polymerase copies the DNA sequence downstream of the TATA box into an mRNA strand.

The answers in the blank spaces:

1. Upstream

2. RNA

3. Terminator

Explanation:

This question is describing the process of transcription, which is the process whereby DNA template is used to synthesize an mRNA molecule. Transcription involves three stages viz: initiation, elongation and termination.

- DNA strands run in 1 of 2 directions depending on which end of the strand is free and which end has a phosphate bond. One direction is 5' to 3' (UPSTREAM) and the other direction is 3' to 5' (downstream). An enzyme called RNA polymerase binds to the DNA at the TATA box and unzips the double helix (INITIATION).

- Working along the DNA chain, RNA polymerase reads the DNA nitrogenous bases and matches RNA nitrogenous bases from the nucleus (uracil instead of thymine). As it moves, RNA polymerase re-zips the DNA behind it and lets the mRNA separate from the DNA (ELONGATION).

- It continues to do this until it reaches a sequence downstream called a TERMINATOR signal (TERMINATION). In other words, RNA polymerase copies the DNA sequence downstream of the TATA box into an mRNA strand.

the three components of a nucleotide are the nitrogenous base, the phosphate group and the five-carbon sugar.