DNA种类

< br>cpDNA:

叶绿体基因组也叫叶绿体

DNA

cpDNA)

，双链环状，每个叶绿体中约含< /p>

12

个

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

-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).