Stop Codons from DNA to MRNA

[bobeanie95]

Hey, so from my understanding the stop codons on RNA are 5'-UAA/UGA/UAG-3'.
Consequently, the DNA is supposed to then have in its sequence 5'-TAA/TGA/TAG-3', which corresponds to stop codons.

However, I'm getting slightly confused how this sequence goes from DNA to mRNA.

For example, if DNA has a sequence: 5'-TGACCCCCCC-3' then RNA polymerase will synthesize complementary (5' to 3') to make 5'GGGGGGGUCA-3'. The ribosome will read the mRNA in the 5' to 3'. However, "UCA" in the mRNA strand doesn't code for a stop codon.

In other words, how does the 5'-TGA-3' from mRNA become 5'-UGA-3' stop codon in mRNA.

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[theonlytycrane]

In other words, how does the 5'-TGA-3' from mRNA become 5'-UGA-3' stop codon in mRNA.

Do you mean how does 5'-TGA-3' from DNA become 5'-UGA-3' in mRNA?

The stop codons UAA / UGA / UAG are 5' to 3' on the mRNA strand.

So if an mRNA strand read 5'-AAAAAAUGA-3', it would have come from a DNA strand that read 5'-TCATTTTTT-3'.

 

[bobeanie95]

Do you mean how does 5'-TGA-3' from DNA become 5'-UGA-3' in mRNA?

The stop codons UAA / UGA / UAG are 5' to 3' on the mRNA strand.

So if an mRNA strand read 5'-AAAAAAUGA-3', it would have come from a DNA strand that read 5'-TCATTTTTT-3'.

Right, but the stop codons on DNA are TAG, TAA, and TGA. "TCA" isn't one of them. I feel like I'm missing something obvious..

 

[victorias]

 

[theonlytycrane]

I guess it depends which stop codons on which strand you're memorizing. I only memorize the codon triplets on the mRNA coding strand because the rest can be derived from them if needed.

As ^ shows, the codon triplets you're looking for are associated with the DNA coding strand. "TCA" would be on the DNA template strand.

 

[bobeanie95]

@victorias thank you!