Nitrogenous base - Wikipedia Nitrogenous base A nitrogenous base, or nitrogen - containing base, is an organic molecule with a nitrogen atom that has the chemical properties of a base. The main biological function of a nitrogenous base is to bond nucleic acids together. A nitrogenous base owes its basic properties to the lone pair of electrons of a nitrogen atom. Nitrogenous bases are typically classified as the derivatives of two parent compounds, pyrimidine and purine. They are non-polar and due to their aromaticity, planar. Both pyrimidines and purines resemble pyridine and are thus weak bases and relatively unreactive towards electrophilic aromatic substitution. Role in nucleic acids Main article : Nucleobase In the biological sciences, nitrogenous bases are increasingly termed nucleobases because of their role in nucleic acids - their flat shape is particularly important when considering their roles as the building blocks of DNA and RNA. A set of five nitrogenous bases is used in the construction of nucleotides, which in turn build up the nucleic acids like DNA and RNA. These nitrogenous bases are adenine ( A ), uracil ( U ), guanine ( G ), thymine ( T ), and cytosine ( C ). These nitrogenous bases hydrogen bond between opposing DNA strands to form the rungs of the `` twisted ladder '' or double helix of DNA or a biological catalyst that is found in the nucleotides. Adenine is always paired with thymine, and guanine is always paired with cytosine. These are known as base pairs. Uracil is only present in RNA, replacing thymine. Pyrimidines include thymine, cytosine, and uracil. They have a single ring structure. Purines include adenine and guanine. They have a double ring structure. References Jump up ^ Nelson, David L. and Michael M Cox ( 2008 ). Lehninger Principles of Biochemistry, ed. 5, W.H. Freeman and Company. p. 272. ISBN 071677108X. Jump up ^ Carey, Francis A. ( 2008 ). Organic Chemistry, ed. 6, Mc Graw Hill. p. 1206. ISBN 0072828374. Jump up ^ Angstadt, Carol N ( 1997 ) Purine and Pyrimidine Metabolism. library.med.utah.edu This biochemistry article is a stub. You can help Wikipedia by expanding it. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Nitrogenous_base&oldid=827994765 '' Categories : Biochemistry Biochemistry stubs Talk About Wikipedia Aragonés Azərbaycanca Башҡортса Català Eesti Español Esperanto Galego Italiano 日本 語 Occitan Português Română Русский کوردی Српски / srpski Srpskohrvatski / српскохрватски தமிழ் ไทย Türkçe Українська 中文 Edit links This page was last edited on 27 February 2018, at 22 : 59. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: when dna makes rna what is the base that replaces thymine
Answer: Uracil