DNA和RNA有何不同,有甚麼用,如何组成?

想像DNA是一部電影的膠卷，RNA是放映的設備，而蛋白質便是一場聲色俱佳的電影！您是否能由這個比喻中，體會到RNA在細胞內所扮演的角色？DNA與RNA的差異到底到哪兒？德國的細胞學家福爾根解開了這個謎題

DNA與RNA的結構差異： DNA是雙鏈，RNA是單鏈
兩者在五碳糖的第二個碳原子上，DNA連接的是氫原子，而RNA連接的是羥基
DNA所含的鹼基種類為ATCG，而RNA為AU（尿嘧啶）CG

2006-10-24 17:16:51 補充：
希望這個令你更易明白！

http://mod.life.nthu.edu.tw/protein/PTRC/Flash/TRANSCRIPTION.SWF

　

遺傳學是研究基因對個體表現的特徵，甚麼是叫基因呢(Gene)，基因是每個人從父母得下來的遺傳基本單元，它決定每個個體表現的特徵，基因十分細小，無法從肉眼可以看見卻藏著生物化學DNA的訊息。排列在人體細胞內的46條染色體

(Chromosome)上-46條染色體可分為23對，包括22對常染色體或者管理身體各種特徵的染色體和另外一對是性染色體，決定個人的性別。當基因運作上出現錯誤，便會導至三種遺傳病例。

Ribonucleic acid (RNA) is a nucleic acid polymer consisting of nucleotide monomers. RNA nucleotides contain ribose rings and uracil unlike deoxyribonucleic acid (DNA), which contains deoxyribose and thymine. It is transcribed from DNA by enzymes called RNA polymerases and further processed by other enzymes. RNA serves as the template for translation of genes into proteins, transferring amino acids to the ribosome to form proteins, and also translating the transcript into proteins.
Nucleic acids were discovered in 1869 by Johann Friedrich Miescher (1844-1895), who called the material 'nuclein' since it was found in the nucleus. It was later discovered that prokaryotic cells, which do not have a nucleus, also contain nucleic acids.

The role of RNA in protein synthesis had been suspected since 1939, based on experiments carried out by Torbjörn Caspersson, Jean Brachet and Jack Schultz.

The sequence of the 77 nucleotides of a yeast RNA was found by Robert W. Holley in 1964, winning Holley the 1968 Nobel Prize for Medicine.

RNA is primarily made up of four different bases: adenine, guanine, cytosine, and uracil. The first three are the same as those found in DNA, but in DNA thymine replaces uracil as the base complementary to adenine. This base is also a pyrimidine and is very similar to thymine. Uracil is energetically less expensive to produce than thymine, which may account for its use in RNA. In DNA, however, uracil is readily produced by chemical degradation of cytosine, so having thymine as the normal base makes detection and repair of such incipient mutations more efficient. Thus, uracil is appropriate for RNA, where quantity is important but lifespan is not, whereas thymine is appropriate for DNA where maintaining sequence with high fidelity is more critical.

There are also numerous modified bases found in RNA that serve many different roles. Pseudouridine (Ψ) and the DNA nucleoside thymidine are found in various places (most notably in the TΨC loop of every tRNA). There are nearly 100 other naturally occurring modified bases, many of which are not fully understood.

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Comparison with DNA
Unlike DNA, RNA is almost always a single-stranded molecule and has a much shorter chain of nucleotides. RNA contains ribose, rather than the deoxyribose found in DNA (there is a hydroxyl group attached to the pentose ring in the 2' position whereas RNA has two hydroxyl groups). These hydroxyl groups make RNA less stable than DNA because it is more prone to hydrolysis. Several types of RNA (tRNA, rRNA) contain a great deal of secondary structure, which help promote stability.

Like DNA, most biologically active RNAs including tRNA, rRNA, snRNAs and other non-coding RNAs (such as the SRP RNAs) are extensively base paired to form double stranded helices. Structural analysis of these RNAs have revealed that they are not, "single-stranded" but rather highly structured. Unlike DNA, this structure is not just limited to long double-stranded helices but rather collections of short helices packed together into structures akin to proteins. In this fashion, RNAs can achieve chemical catalysis, like enzymes. For instance, determination of the structure of the ribosome in 2000 revealed that the active site of this enzyme that catalyzes peptide bond formation is composed entirely of RNA.