why thymine is used in dna than uracil?

1. DNA VS RNA
BY:SHEIKH AMIR HAMZA
256-FBAS-BSBT-F12
DEPARTMENT OF BIOINFORMATICS AND BIOTECHNOLOGY IIUI.

2. DNA
DNA is a chemical compound that resembles a long chain,
with the links in the chain made up of individual chemical
units called nucleotides. The nucleotides themselves have
three components: a sugar (deoxyribose), phosphate, and
a nucleobase
 Adenine
 Guanine
 Cytosine
 Thiamine

3. RNA
RNA acts as a messenger between DNA and the protein synthesis
complexes known as ribosomes, forms vital portions of ribosomes, and
acts as an essential carrier molecule for amino acids to be used in protein
synthesis.
RNA is very similar to DNA, but differs in a few important structural details:
 RNA is single stranded, while DNA is double stranded.
 RNA nucleotides contain ribose sugars while DNA contains
deoxyribose.
 RNA uses predominantly uracil instead of thymine present in DNA.

4. Question Arises?
Why Uracil Instead Of Thymine?
OR BETTER YET
Why Thymine Instead Of Uracil?

5. Molecular Biology of the Cell. 4th
edition!
 Currently it’s highly accepted that RNA was the first nucleic acid to
exist and that DNA evolved from it, so the changes in the sugar and
one of the nitrogenous bases must have some advantage.
“RNA stored both genetic information and catalyzed the chemical
reactions in primitive cells. Only later in evolutionary time did DNA take
over as the genetic material.”

6. To Understand!
 Let’s compare cytosine, uracil and thiamine.
 The only difference between uracil and thymine is the presence of a methyl
group at the last carbon.
uracil thiaminecytosine

7. Formation Of Uracil
 Cytosine is readily deaminated, forming uracil.
 This occurs at a rate of 1,000 to 10,000 times per cell per day.
 This altered base is recognized very efficiently by uracil DNA
glycosylase (UDG).
 This site is then removed and replaced by cytosine, restoring the
DNA back to its original and correct sequence.
 This process of repair is referred to as base excision repair (BER) and
is probably the major system responsible for maintaining the integrity
of the cell’s DNA.

8. Coming To Conclusion!
 Why DNA uses thiamine instead of uracil?
 One reason is to protect the DNA. Methylation of bases protects the
DNA by making it unrecognizable to many nucleases enzymes that
can break down DNA.
 Also, adding the hydrophobic methyl group changes the shape of
the DNA molecule and allows thymine to base-pair only with
adenine, whereas uracil would base-pair less selectively.
 If uracil were present in DNA, then the cell would have a difficult
time deciding whether the uracil generated from a mutation—the
deamination of cytosine should be there or not.

9. Continue!
 Why RNA uses Uracil instead of thiamine?
 Since RNA is shorter-lived than DNA, it can get by with the
energetically “cheaper” uracil.
 A second possibility is that RNA polymerase evolved to prefer uracil
so as not to compete with DNA polymerases for thymine in primitive
cells (uracil was recognized better by the RNA Polymerase).

10. References
 http://www.ncbi.nlm.nih.gov/books/NBK26876/
 https://earthlingnature.wordpress.com/2012/09/29/why-thymine-
instead-of-uracil/
 http://www.nsta.org/publications/news/story.aspx?id=5260
 http://www.sciencedaily.com/terms/rna.htm
 http://microbe.net/simple-guides/fact-sheet-dna-rna-protein/