用DNAman分析引物时，Thermo Tm、Hybridization Tm、GC+AT Tm分别是什么意思？急！！！

The melting temperature of an oligonucleotide is

calculated with three methods:

1)Thermodynamic Tm:

The Tm is calculated using the nearest-neighbor

thermodynamic values method (Breslauer et al). This method is less accurate for

longer oligos. The formula for the Tm is

Tm=dH/(dS-Rln(Cd))-273.15+16.6*(log10(Cs))

Where dH is the enthalpy, dS is the

entropy, R is 1.987 cal K-1 mol-1, Cd is the

DNA concentration, and Cs is the salt concentration.

2)Hybridisation Tm:

This method is generally used for DNA or RNA

hybridization, especially in presence of high salt and formamide. It is more

accurate with longer oligos. The Tm is calculated using the following

formula:

for DNA:DNA hybridization:

Tm=81.5+16.6*(log10[Na+])+0.41*[%(G+C)]-0.63*(%Formamide)-500/L-1.5(%Mismatch)

for DNA:RNA hybridization:

Tm=79.8+18.5*(log10[Na+])+0.58*[%(G+C)]+11.8*[%(G+C)]2-0.5*(%Formamide)-820/L-1.5(%Mismatch);

for RNA:RNA hybridization:

Tm=79.8+18.5*(log10[Na+])+0.58*[%(G+C)]+11.8*[%(G+C)]2-0.35*(%Formamide)-820/L-1.5(%Mismatch);

* where L is the length (bases) of the

oligonucleotide.

3)GC+AT Tm: the estimated Tm is the sum of

the contribution of each base: 2°C for A and T and 4°C for G and C.

There are several parameters involved in Tm

calculation.

DNA concentration is used only in

thermodynamic Tm. You may increase oligo DNA concentration in order to increase

Tm.

Salt concentration affects thermodynamic Tm

and hybridization Tm. In the [Na+][mM] box, you may type a suitable salt

concentration of your experiments. The value must be an integer greater than

0.

Hybridization type is required for

Hybridization Tm. In the DNA/RNA box, enter the hybridization type:

dna的tm值和at含量有关at含量高则tm高

这句话是错误的

是Tm值和GC含量有关，GC含量高则Tm高

DNA的化学结构：

①DNA是高分子化合物：组成它的基本元素是C、H、O、N、P等.

②组成DNA的基本单位——脱氧核苷酸.每个脱氧核苷酸由三部分组成：一个脱氧核糖、一个含氮碱基和一个磷酸

③构成DNA的脱氧核苷酸有四种.DNA在水解酶的作用下,可以得到四种不同的核苷酸,即腺嘌呤（A）脱氧核苷酸；鸟嘌呤（G）脱氧核苷酸；胞嘧啶（C）脱氧核苷酸；胸腺嘧啶（T）脱氧核苷酸；组成四种脱氧核苷酸的脱氧核糖和磷酸都是一样的,所不相同的是四种含氮碱基：ATGC.

④DNA是由四种不同的脱氧核苷酸为单位,聚合而成的脱氧核苷酸链.2、DNA的双螺旋结构：DNA的双螺旋结构,脱氧核糖与磷酸相间排列在外侧,形成两条主链（反向平行）,构成DNA的基本骨架.两条主链之间的横档是碱基对

在双链DNA分子中,一条链中的不互补的两碱基含量之和的比值（A+T/G+C）与其在互补链中的比值和在整个分子中的比值都是一样的.

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