Coding and non-Coding vs Leading and Lagging strands?

[SStell]

Is the coding strand of the DNA always the same as the leading strand being replicated?

Or is there no correlation what-so-ever?

My question arises from the incredibly more elaborate synthesis process occurring on the lagging strand. Sure it's being copied in the opposite direction and needs to be moved about to accommodate that fact, but it seems to be even more than that to me.

[CharonY]

Transcription can occur in either strand. As mRNA is of much shorter length and is synthesized as a single continuous molecule it does not have the same issue as DNA-replication.

That being said, there are interactions e.g. of the transcription and replication apparatus that can result different properties, depending on which strand the gene is being transcribed.

[SStell]

CharonY, so are you saying that the coding/noncoding strand does not mean the same thing as the leading and lagging strand?

And can RNA be transcribed from both DNA strands?

[CharonY]

Yes. The polymerase can only work 5'-3' but it can go on either strand. Leading and lagging strand is relevant with respect to replication, not transcription (with the caveats mentioned above).

[SStell]

Charon, so there are two strands of DNA.

In DNA replication one is called the leading strand and the other is the lagging strand.

In RNA synthesis transcription one DNA strand is the coding strand and the other is called the non-coding strand.

 

Now, are you saying that both DNA strands may be used to synthesis or transcribe RNA?

If so, doesn't that change our genome from `3 billion bases to `6 billion? Or am I just very confused?

 

In DNA replication is there a determining factor that leads to the determination of which strand will be the leading strand and which will be the lagging strand or is just completely arbitrary and does not matter at all?

[CharonY]

You are confusing different elements to a degree. First, you must recognize (and I think implicitly you do but may not be quite clear about the ramifications) that the need for the lagging mechanisms is because replication happens on both strands at the replication fork. The polymerase has 5'-3' activity and can therefore only proceed without lagging on one of the strands.

 

However, if you transcribe a gene only one strand is read at any given time, so the RNA polymerase can continue to move.

Moreover, the polymerase reads everything during replication, however transcription is only initiated at open reading frames. They can be on the one, or the other strand though. I.e. if the recognition is one the one strand, it will bind there, if it is the other one. I.e. there is not one strand that is completely sense or anti-sense. It all depends in relation to the transcription initiation. Note that in most eukaryotes ORFs are only a tiny proportion of the genome and typically you won't find many examples of genes that overlap at a given locus. I.e. gene products are generally only produced from one or the other stand from a given site.

In smaller genomes, especially viral ones, this is not the case, however.

 

None of this changes the genome size. The number only refers to the number of base pairs.

[SStell]

Charon, thanks.

 

I am not trying to make a pest of myself but I just want to make sure I got this correct in my head.

 

So in DNA replication the polymerases need to synthesize in opposite directions from the replication fork and one strand is called the leading strand and the other is called the lagging strand and that they are chosen arbitrarily?

 

I understand the NEED for the lagging strand mechanisms but I am having a hard time seeing the evolution of those mechanisms.

I asked this question as a separate topic on the evolution section and have not received a single reply.

 

 

Now- you are stating that both strands of the DNA can and do code for RNAs? And that the templates do not overlap too often?

Here are the two strands of DNA- A and B

 

A ---------------------------------- -------------------------- ---------------------------

B ----------------- ---------------------------- -----------------------

 

and the dashed lines are templates for some type of RNA. Is this somewhat correct? And the gaps are just non-coding sections?

 

 

[BabcockHall]

"So in DNA replication the polymerases need to synthesize in opposite directions from the replication fork and one strand is called the leading strand and the other is called the lagging strand and that they are chosen arbitrarily?" Assuming that we are talking about E. coli, there are two replication forks that move in opposite directions. Each one has two copies of DNA polymerase III, but there are different accessory proteins. The synthesis of the leading strand is continuous, and it is much simpler and requires fewer proteins. The synthesis of the lagging strand is not continuous, and so is more complex.

[Xalatan]

Leading and lagging strands in general refer to the process of DNA replication. Both strands Are synthesised 5'-->3', but since the replication proceeds in a direction one strand has to be fragmented in Its synthesis, later patched up by DNA ligase. Hence the terms leading and lagging strands.

 

Coding and non-coding strands generally refer to the process of transcription. The coding strand is the non-transcribed strand running 5'-->3', while the non-coding strand is the transcribed strand running 3'-->5'. The coding strand is named because it should be exactly the same as the mrna except thymidine is substituted for uracil.

[SStell]

Thanks

So the names are just based on the activity occuring.