Phosphodiester bond 505575 210697822 2008-05-07T00:32:04Z 89.27.25.164 [[Image:PhosphodiesterBondDiagram.png|thumb|200px|Diagram of phosphodiester bonds between nucleotides]] A '''phosphodiester bond''' is a group of strong covalent bonds between the [[Phosphorus|phosphorus atom]] in a [[phosphate group]] and two other [[molecule]]s over two [[ester]] bonds. Phosphodiester bonds are central to all life on [[Earth]], as they make up the backbone of the [[DNA|strands of DNA]]. In DNA and [[RNA]], the phosphodiester bond is the linkage between the 3' [[carbon]] [[atom]] and the 5' carbon of the sugar [[deoxyribose]] (in DNA) or [[ribose]] (in RNA). The phosphate groups in the phosphodiester bond are negatively-charged. Because the phosphate groups have a [[Equilibrium constant|pK<sub>a</sub>]] near 0, they are negatively-charged at pH 7. This repulsion forces the phosphates to take opposite sides of the DNA strands and is neutralized by proteins ([[histones]]), metal ions, and polyamines. In order for the phosphodiester bond to be formed and the [[nucleotide]]s to be joined, the tri-phosphate or di-phosphate forms of the nucleotide building blocks are broken apart to give off energy required to drive the [[Enzyme|enzyme-catalyzed]] reaction. When a single phosphate or two phosphates known as [[pyrophosphate]]s break away and catalyze the reaction, the phosphodiester bond is formed. Hydrolysis of phosphodiester bonds can be catalyzed by the action of [[phosphodiesterase]]s which play an important role in repairing DNA sequences. In biological systems, the phosphodiester bond between two [[ribonucleotide]]s can be broken by [[alkaline hydrolysis]] because of the free 2' [[Hydroxyl|hydroxyl group]]. == Enzyme activity == A [[phosphodiesterase]] is an [[enzyme]] that [[catalyzes]] the [[hydrolysis]] of phosphodiester bonds, for instance a bond in a molecule of [[cyclic adenosine monophosphate|cyclic AMP]] or [[Cyclic guanosine monophosphate|cyclic GMP]]. An enzyme that plays an important role in the repair of [[Oxidation|oxidative]] [[DNA repair|DNA damage]] is the 3'-phosphodiesterase. During [[DNA replication|the replication of DNA]], there is a hole between the phosphates in the backbone left by [[DNA polymerase I]]. [[DNA ligase]] is able to form a phosphodiester bond between the [[nucleotide]]s. == See also == *[[Phosphodiesterase]] *[[Phosphodiesterase inhibitor]] *[[DNA replication]], [[DNA]], [[Adenosine triphosphate|ATP]] *[[Teichoic acid]], [[DNase I]] *[[PDE5]] [[Category:Chemical bonding]] [[Category:Molecular biology]] [[Category:Biology and pharmacology of chemical elements]] [[Category:Phosphorus compounds]] [[Category:Oxygen compounds]] [[es:Enlace fosfodiéster]] [[fr:Lien phosphodiester]] [[he:קשר פוספודיאסטרי]] [[ja:ホスホジエステル結合]] [[pl:Wiązanie fosfodiestrowe]] [[ru:Фосфодиэфирная связь]] [[zh:磷酸雙酯鍵]]