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DNA种类

作者:高考题库网
来源:https://www.bjmy2z.cn/gaokao
2021-02-10 03:42
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2021年2月10日发(作者:orea)


一、脱氧核糖核酸



cDNA:


互补


DNA



Complem entary DNA



cDNA


)< /p>


是一种利用逆转录酶,



RNA


(通常是


mRNA



为 模板作成的复制品,经常用来将真核生物的基因(以


mRNA


形 式)复制到原核生物细胞


中。若一个


cDNA

< br>含有许多来自不同基因的


mRNA


,称为


cDNA


基因库(


cDNA library



。另外


也可制成只含单一

mRNA



cDNA


< p>
(from wiki)



< br>cpDNA:


叶绿体基因组也叫叶绿体


DNA

< p>


cpDNA)


,双链环状,每个叶绿体中约含< /p>


12



cpDNA


分子。


叶绿体具有独立基因组,


被认为是内共生起源的细胞器 。


叶绿体基因组主要用于编码


与光合作用密切相关的一些蛋白和 一些核糖体蛋白。


叶绿体基因表达调控是在不同水平上进


行的, 光和细胞分裂素对叶绿体基因的表达也起着重要的调节作用。



gDNA: Genomic DNA.


是区别与染色体之外的


DNA


,如质粒


DNA


等。


gDNA


可以遗传给后代。




msDNA



Multicopy


single-stranded DNA (msDNA)


is a type


of extrachromosomal satellite DNA


that consists of a single-stranded DNA molecule covalently linked via a 2'-5'phosphodiester bond


to


an


internal


guanosine


of


an


RNA


molecule.


The


resultant


DNA/RNA


chimera


possesses


two


stem-loops


joined


by a


branch similar to the branches found


in RNA


splicing intermediates. The


coding region for msDNA, called a


essential for msDNA synthesis.[2]





mtDNA



Mitochondri al


DNA


(mtDNA


or


mDNA[2])


is


the


DNA


located


in


organelles


called


mitochondria, structures within eukaryotic cells that convert the chemical energy from food into


a form that cells can use, adenosine triphosphate (ATP). Most


other DNA


present


in eukaryotic


organisms is found in the cell


是母系遗传的。




rDNA:


Ribosomal


DNA


(rDNA)


codes


for


ribosomal


RNA.


The


ribosome


is


an


intracellular


macromolecule


that


produces


proteins


or


polypeptide


chains.


The


ribosome


itself


consists


of


a


composite of proteins and RNA. As shown in the


figure, rDNA consists of a tandem repeat of a


unit segment, an operon, composed


of NTS, ETS, 18S, ITS1, 5.8S, ITS2, and 28S tracts. rDNA has


another gene, coding for 5S rRNA, located in the genome in most eukaryotes.[1] 5S rDNA is also


present


in


tandem


repeats


as


in


Drosophila.[1]


In


the


nucleus,


the


rDNA


region


of


the


chromosome is visualized as a nucleolus which forms expanded chromosomal loops with rDNA.


These rDNA regions are also called nucleolus organizer regions, as they give rise to the nucleolus.


In the human genome there are 5 chromosomes with nucleolus organizer regions: chromosomes


13,14,15,21 and 22.


染色体上编码


rRNA


的基因。






二、核糖核酸:



mRNA

< p>
(前


-mRNA/


不均一核


RNA



Messenger RNA (mRNA) is a molecule of RNA that encodes a


chemical



for


a


protein


product.


mRNA


is


transcribed


from


a


DNA


template,


and


carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid


polymer


is


translated


into


a


polymer


of


amino


acids:


a


protein.


In


mRNA,


as


in


DNA,


genetic


information


is encoded in the sequence


of nucleotides arranged into codons consisting of three


bases


each.


Each


codon


encodes


for


a


specific


amino


acid,


except


the


stop


codons,


which


terminate protein synthesis. This process requires two other types of RNA: Transfer RNA (tRNA),


that


mediates


recognition


of


the


codon


and


provides


the


corresponding


amino


acid,


and


ribosomal


RNA


(rRNA),


that


is


the


central


component


of


the


ribosome's


protein


-manufacturing


machinery.



tRNATransfer


RNA


(tRNA)


is


an


adaptor


molecule


composed


of


RNA,


typically


73 to 93 nucleotides in length, that is used in biology to bridge the


four-letter genetic code (ACGU) in messenger RNA (mRNA) with the


twenty-letter


code


of


amino


acids


in


proteins.[1]


The


role


of


tRNA


as


an


adaptor is best understood by considering its three-dimensional


structure.




rRNA



Ribosomal ribonucleic acid (rRNA) is the RNA component of the


ribosome,


the


enzyme


that


is


the


site


of


protein


synthesis


in


all


living


cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino


acids and interacts with tRNAs during translation by providing


peptidyltransferase


activity.


The


tRNAs


bring


the


necessary


amino


acids


corresponding to the appropriate mRNA codon.


Inside the ribosome



The ribosomal RNAs form two subunits, the large subunit (LSU) and small


subunit (SSU). mRNA is sandwiched between the small and large subunits


and the ribosome catalyzes the formation of a peptide bond between the


2 amino acids that are contained in the rRNA.


A ribosome also has 3 binding sites called A, P, and E.


The A site in the ribosome binds to an aminoacyl-tRNA (a tRNA bound to


an amino acid).


The


amino


(NH2)


group


of


the


aminoacyl- tRNA,


which


contains


the


new


amino


acid, attacks the ester linkage of peptidyl-tRNA (contained within the


P


site),


which


contains


the


last


amino


acid


of


the


growing


chain,


forming


a new peptide bond. This reaction is catalyzed by peptidyltransferase.


The tRNA that was holding on the last amino acid is moved to the E site,


and what used to be the aminoacyl-tRNA is the peptidyl-tRNA.


A single mRNA can be translated simultaneously by multiple ribosomes.


Prokaryotes vs. Eukaryotes


Both prokaryotic and eukaryotic ribosomes can be broken down into two


subunits (the S in 16S represents Svedberg units


沉降单位


):



Note


that


the


S


units


of


the


subunits


cannot


simply


be


added


because


they


represent measures of sedimentation rate rather than of mass. The


sedimentation rate of each subunit is affected by its shape, as well as


by its mass.



Prokaryotes


In prokaryotes a small 30S ribosomal subunit contains the 16S rRNA.


The


large


50S


ribosomal


subunit


contains


two


rRNA


species


(the


5S


and


23S


rRNAs).

-


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