Both RNA and DNA are composed of repeated units. The repeating units of RNA are ribonucleotide monophosphates and of DNA are 2'-deoxyribonucleotide monophosphates.
Both RNA and DNA form long, unbranched polynucleotide chains in which different purine or pyrimidine bases are joined by N-glycosidic bonds to a repeating sugar-phosphate backbone.
The chains have a polarity. The sequence of a nucleic acid is customarily read from 5' to 3'. For example the sequence of the RNA molecule is AUGC and of the DNA molecule is ATGC
The base sequence carries the information, i.e. the sequence ATGC has different information that AGCT even though the same bases are involved.
Consequences of RNA/DNA chemistry
The DNA backbone is more stable, especially to alkaline conditions. The 2' OH on the RNA forms 2'3'phosphodiester intermediates under basic conditions which breaks down to a mix of 2' and 3' nucleoside monophosphates. Therefore, the RNA polynucleotide is unstable.
The 2' deoxyribose allows the sugar to assume a lower energy conformation in the backbone. This helps to increase the stability of DNA polynucleotides. The following link shows 3-D models of the DNA and RNA nucleotides.
Cytidine deamination to Uridine can be detected in DNA but not RNA because deamination of Cytidine in DNA leads to Uridine not Thymidine. Uridine bases in DNA are removed by a specific set of DNA repair enzymes and replaced with cytidine bases.
DNA carries the genetic information of a cell and consists of thousands of genes. Each gene serves as a recipe on how to build a protein molecule. Proteins perform important tasks for the cell functions or serve as building blocks. The flow of information from the genes determines the protein composition and thereby the functions of the cell.
The DNA is situated in the nucleus, organized into chromosomes. Every cell must contain the genetic information and the DNA is therefore duplicated before a cell divides (replication). When proteins are needed, the corresponding genes are transcribed into RNA (transcription). The RNA is first processed so that non-coding parts are removed (processing) and is then transported out of the nucleus (transport). Outside the nucleus, the proteins are built based upon the code in the RNA (translation).
The document has two levels, basic and advanced. This page is an introduction to both levels. You start at the basic level, then you can advance if you want more and deeper information.
Virüslerde DNA ve RNA neden birlikte bulunmaz? (Sema Özdeş)
Virüsler temelde genetik madde (çekirdek asitleri) dışında başka bir şey içermiyorlar. Bu çekirdek asitlerini de, konak canlılara ileterek, onların hücre bileşenlerini kullanarak kendilerini çoğaltıyorlar. DNA içeren virüsler doğrudan DNA’larını konak canlı genomuna entegre edebilirken, RNA içeren virüsler önce RNA’larını DNA’ya dönüştürmek (daha doğrusu konak canlıya dönüştürtmek) zorunda kalıyorlar. Ancak, RNA içermelerinin de bir avantajı var. DNA’dan daha az korunaklı olan RNA, daha kolay mutasyon geçirebiliyor ve bu da bir virusun olumsuz koşullar karşısında genetik yapısını çok daha rahat değişime uğratabilmesi anlamına geliyor.
Virüsler zaten her iki genetik materyalden birine sahip olarak varlıklarını başarıyla sürdürebiliyorlar. DNA ya da RNA içermelerine göre farklı özelliklere sahip olmaları da bir diğer avantaj. Genetik bilgileri kullanabilecek organelleri içermemeleri nedeniyle de, fazladan genetik materyal içermelerine gerek yok.
Deniz Candaş
Daha Yeni Kayıtlar Önceki Kayıtlar Ana Sayfa
