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A base is an organic nitrogenous [[Molecule|molecule]] which, when [[ | A base is an organic nitrogenous [[Molecule|molecule]] which, when [[Covalent bond|covalently]] bonded to a [[Pentose sugar|pentose sugar]], forms a [[Nucleotide|nucleotide]], which is in turn linked to phosphate molecules. There are four types of bases in [[DNA|DNA]]: [[Adenine|adenine]], [[Thymine|thymine]], [[Guanine|guanine]] and [[Cytosine|cytosine]]. Generally, [[Purine|purine]] bases such as [[Adenine|adenine]] and [[Guanine|guanine]] form [[Hydrogen bonds|hydrogen bonds]] with [[Pyrimidine|pyrimidine]] bases such as [[Thymine|thymine]] and [[Cytosine|cytosine]]. According to [[Watson-Crick|Watson-Crick]] principles in [[DNA|DNA]], [[Adenine|adenine]] only base pairs with [[Thymine|thymine]] and [[Cytosine|cytosine]] only base pairs with [[Guanine|guanine]]. Strong [[Hydrogen bonds|hydrogen bonds]] form between complementary bases A and T or C and G. These [[Hydrogen bonds|hydrogen bonds]] are broken during [[Semi-conservative replication|semi-conservative replication]] so the [[DNA|DNA]] [[Molecule|molecule]] can unwind. In RNA, thymine is replaced with uracil, complementary base pairing with A. They both have a similar structure apart from uracil lacks the 5' methyl group. | ||
Revision as of 19:43, 20 October 2012
A base is an organic nitrogenous molecule which, when covalently bonded to a pentose sugar, forms a nucleotide, which is in turn linked to phosphate molecules. There are four types of bases in DNA: adenine, thymine, guanine and cytosine. Generally, purine bases such as adenine and guanine form hydrogen bonds with pyrimidine bases such as thymine and cytosine. According to Watson-Crick principles in DNA, adenine only base pairs with thymine and cytosine only base pairs with guanine. Strong hydrogen bonds form between complementary bases A and T or C and G. These hydrogen bonds are broken during semi-conservative replication so the DNA molecule can unwind. In RNA, thymine is replaced with uracil, complementary base pairing with A. They both have a similar structure apart from uracil lacks the 5' methyl group.