How does cell machinery distinguish between the template & coding strand?

[Koilon]

The topic title says it all. How does the machinery of the cell distinguish between the template and coding strands of the DNA double helix? If it transcribed the coding strand, instead of the template strand, the resulting protein would be wrong.

[CharonY]

Which strand is being transcribed is determined during the initiation step where RNA-promoter binding happens. In other words the the initiation is sequence-specific, which is also a prerequisite as if transcription started somewhere randomly, you would not get a functional mRNA, either. Essentially the polymerase, together with transcription factor identify the cognate promoter. In bacteria it is fairly straightforward (look up the -10 and -35 consesus region). In eukaryotes it is slightly more complex insofar that transcription factors are now mandatory and often involve the TATA box (which is somewhat similar to bacterial -10).

Edited June 20, 2016 by CharonY

[Velocity_Boy]

The topic title says it all. How does the machinery of the cell distinguish between the template and coding strands of the DNA double helix? If it transcribed the coding strand, instead of the template strand, the resulting protein would be wrong.

 

 

I will do my best to answer in the most simplified way possible:

 

Mitochondrial DNA or mtDNA is thought to have a separate evolutionary origin than nuclear DNA.

 

 

OK...so, it's now thought that mitochondria originated when an early ancestor of eukaryotic cells engulfed a Proteobacterial cell (whether because the cell was going to "eat" the bacteria or because the bacteria was going to be a parasite--although I think the latter is more plausible). Instead of digesting the bacterium completely the cell derived energy from it and the proto-mitochondria was able to survive and reproduce in this environment.

 

Eventually much of the the endosymbiont's (the bacteria's) genome became incorporated into the host cell and became what we now would know as an organelle.

 

We have evidence to support the hypothesis that mitochondria originated from a bacterial cell:

1. Mitochondria divide in a cell in a way that is very similar to bacterial cells
2. Mitochondria contain their own circular (like a bacterial cell!) DNA and the genome is similar to bacterial species that are thought to be related
3. They have a transport proteins in their outer membranes called porins and have ribosomes that are similar to bacteria
4. If the mitochondria are removed from a cell it will be unable to create new ones.

There is more evidence but these are just some of the simpler ones.

[CharonY]

Uhm, what does it have to do with the OP?