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Double stranded vs. single standed. Please help!

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Double stranded vs. single standed. Please help!

Postby varo650 » Thu Oct 12, 2006 6:41 am

Ok, so i am stuck on one of my homework question and was wondering if anyone could help. The question is:

Why is it functionally appropriate that DNA is double stranded and that RNA is single stranded?

I have been searching and reading and have gotten nowhere. Any help would be greatly appreciated...even something to get me started or something to think about.

Thanks
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Postby rambo » Thu Oct 12, 2006 9:50 am

Functionally appropriate?
RNA and its one strand nature.
Well one big reason why Rna couldnt be double stranded is because its one stranded nature might make it easier to transport out the nucleus.
double strand will make it harder to move out the nucleus. Once out, of course it being now titled as mrna if not trna. it can also use the one stranded nature to bond with ribosomes and make protein.
DNA and its two stranded nature.
DNA contains the most important information for your body and your future generation. Having such a role as containing the most important info, its must have some kind of form of protection to keep that information in your genes protected. its double helix form i believe forms a frame work that makes it stable. Stable because ever base is attached to its proper partner base. In RNA bases are open until needed not to be.
Hope that helps
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Postby Dr.Stein » Fri Oct 13, 2006 2:36 am

Yes. Virus is a "cunning" creature that able to "hijack" its host :twisted: However, virus with RNA is "smart" one :)
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Postby lara » Sat Oct 14, 2006 10:05 am

+
RNA is easy to act upon so that introns are removed before translation.
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Postby druid » Sat Oct 14, 2006 3:21 pm

Why DNA, not RNA? ;)

1)
RNA uses ribose whereas DNA uses deoxyribose. Deoxyribose lacking -OH on 2-C atom cannot attack its own carbon backbone chain, thus rendering DNA more chemically stable than RNA and much greater lenghtes of DNA can be maintained without breakage.

2)
RNA's bases are C=G, A=U
DNA's bases are C=G, A=T

Suppose now, there's spontaneous deamination of Cytosine base
(deamination occurs at rate= 100 bases per cell per day, so enough rapid)
But Cytosine + H2O -> Uracil + NH3.
Thus, even mutation has occured, excision repair system (ERS) of the cell ( droven by AP glycosylases) will not detect it, because uracil is naturally occuring nucleotide.
Therefore, using Thymine (methylated uracil) secures that on deamination event the mutation will be detected by excision system.

3) The double helix is ideal for reparation

Molecular Biology of the Cell, 4rd ed, Alberts:
http://www.ncbi.nlm.nih.gov/entrez/quer ... on.827#834

The DNA Double Helix Is Readily Repaired

The double-helical structure of DNA is ideally suited for repair because it carries two separate copies of all the genetic information—one in each of its two strands. Thus, when one strand is damaged, the complementary strand retains an intact copy of the same information, and this copy is generally used to restore the correct nucleotide sequences to the damaged strand.

An indication of the importance of a double-stranded helix to the safe storage of genetic information is that all cells use it; only a few small viruses use single-stranded DNA or RNA as their genetic material. The types of repair processes described in this section cannot operate on such nucleic acids, and the chance of a permanent nucleotide change occurring in these single-stranded genomes of viruses is thus very high. It seems that only organisms with tiny genomes can afford to encode their genetic information in any molecule other than a DNA double helix.

Each cell contains multiple DNA repair systems, each with its own enzymes and preferences for the type of damage recognized. As we see in the rest of this section, most of these systems use the undamaged strand of the double helix as a template to repair the damaged strand.
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