Why Did Mother Nature Use Uracil to Replace Thymine in mRNA (Messenger Ribonucleic Acid)? What Is the Advantage of Using U Instead of T in the RNA?

By Freyer, Greg A.; Sturr, Michael | The Science Teacher, October 2006 | Go to article overview

Why Did Mother Nature Use Uracil to Replace Thymine in mRNA (Messenger Ribonucleic Acid)? What Is the Advantage of Using U Instead of T in the RNA?


Freyer, Greg A., Sturr, Michael, The Science Teacher


Byline: Greg A. Freyer, Ph.D., and Michael Sturr

Question

Why did mother nature use uracil to replace thymine in mRNA (messenger ribonucleic acid)? What is the advantage of using U instead of T in the RNA?

Al Frisby, Biology Teacher, Liberty High School, Liberty, MO

From the Editors: This is a good question, an interesting extension of Paleogenetics, the study of ancient DNA. Here we wonder not just what the genetic encoding looked like, but how it came to be. A better question may be: Why does thymine replace uracil in DNA? Since it takes energy to convert uracil to thymine (by adding a methyl group), why do cells expend the energy required to methylate uracil to thymine for use in DNA?

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-and thus defending it from attack by invaders like bacteria and viruses. Since RNA is shorter-lived than DNA, it can get by with the energetically "cheaper" uracil. 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. Finally, using thymine allows more effective recognition and repair of potentially harmful cytosine to uracil mutations, as explained by Dr. Greg Freyer.

Answer

In DNA, 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), which cleaves it creating an abasic site. 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. For example, BER is responsible for repairing abasic sites, some types of DNA damage caused by UV light (a physical carcinogen), and many other types of DNA damage (e.g., chemical carcinogens such as benzene; or biological carcinogens such as the HIV virus). …

The rest of this article is only available to active members of Questia

Already a member? Log in now.

Notes for this article

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items
Notes
Cite this article

Cited article

Style
Citations are available only to our active members.
Buy instant access to cite pages or passages in MLA 8, MLA 7, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

(Einhorn 25)

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Note: primary sources have slightly different requirements for citation. Please see these guidelines for more information.

Cited article

Why Did Mother Nature Use Uracil to Replace Thymine in mRNA (Messenger Ribonucleic Acid)? What Is the Advantage of Using U Instead of T in the RNA?
Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this article

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Help
Full screen
Items saved from this article
  • Highlights & Notes
  • Citations
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

matching results for page

    Questia reader help

    How to highlight and cite specific passages

    1. Click or tap the first word you want to select.
    2. Click or tap the last word you want to select, and you’ll see everything in between get selected.
    3. You’ll then get a menu of options like creating a highlight or a citation from that passage of text.

    OK, got it!

    Cited passage

    Style
    Citations are available only to our active members.
    Buy instant access to cite pages or passages in MLA 8, MLA 7, APA and Chicago citation styles.

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

    "Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

    1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

    Cited passage

    Thanks for trying Questia!

    Please continue trying out our research tools, but please note, full functionality is available only to our active members.

    Your work will be lost once you leave this Web page.

    Buy instant access to save your work.

    Already a member? Log in now.

    Search by... Author
    Show... All Results Primary Sources Peer-reviewed

    Oops!

    An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.