关于核酸及核苷酸的基本换算

1．核酸的换算： 
(1.1) 摩尔数与质量： 
1 mg 1,000bp DNA = 1.52 pmol
1 mg pUC18/19 DNA (2,688bp) = 0.57 pmol
1 mg pBR322 DNA (4,361bp) = 0.35 pmol
1 mg SV40 DNA (5,243bp) = 0.29 pmol
1 mg FX174 DNA (5,386bp) = 0.28 pmol
1 mg M13mp18/19 DNA (7.250bp) = 0.21 pmol
1 mg l phage DNA (48,502bp) = 0.03 pmol

1 pmol 1,000bp DNA = 0.66 mg
1 pmol pUC18/19 DNA (2,688bp) = 1.77 mg
1 pmol pBR322 DNA (4,361bp) = 2.88 mg
1 pmol SV40 DNA (5,243bp) = 3.46 mg
1 pmol FX174 DNA (5,386bp) = 3.54 mg
1 pmol M13mp18/19 DNA (7.250bp) = 4.78 mg
1 pmol l phage DNA (48,502bp) = 32.01 mg

 (1.2) 光吸收值与浓度： 
1 OD260 dsDNA = 50 mg/ml = 0.15 mmol/L
1 OD260 ssDNA = 33 mg/ml = 0.10 mmol/L
1 OD260 ssRNA = 40 mg/ml = 0.12 mmol/L
1 mmol/L dsDNA = 6.7 OD260
1 mmol/L ssDNA = 10.0 OD260
1 mmol/L ssRNA = 8.3 OD260

 (1.3) 分子量： 
1个脱氧核糖核酸碱基的平均分子量为333 Daltons
1个核糖核酸碱基的平均分子量为340 Daltons

 (1.4) 核酸末端浓度： 
环状DNA： 
pmol ends = pmol DNA ′ number of cuts ′ 2
线性DNA：
pmol ends = pmol DNA ′ (number of cuts ′ 2 + 2)

 1 mg 1,000bp DNA = 3.04 pmol ends
1 mg pUC18/19 DNA (2,688bp) = 1.14 pmol ends
1 mg pBR322 DNA (4,361bp) = 0.7 pmol ends
1 mg SV40 DNA (5,243bp) = 0.58 pmol ends
1 mg FX174 DNA (5,386bp) = 0.56 pmol ends
1 mg M13mp18/19 DNA (7.250bp) = 0.42 pmol ends
1 mg l phage DNA (48,502bp) = 0.06 pmol ends

 2．核苷酸的换算： 
(2.1) 分子量： 
MW (Da) = 333 ′ N (number of bases)

(2.2) 浓度： 
C (mmol/L or pmol/ml) = OD260 / (0.01 ′ N)
C (ng/ml) = OD260 ′ MW / (0.01 ′ N)
MW —— molecular weight
N —— number of bases
OD260 —— absorbance at 260 nm

(2.3) 双链DNA与寡核苷酸的熔点 
短于25bp的双链寡核苷酸： 
Tm = 2 (A + T) + 4 (G + C)
长于25bp的双链寡核苷酸： 
Tm = 81.5 + 16.6 ( lg[J+] ) + 0.41 (%GC) 
– (600/N) – 0.63 (%Formamide)
N —— 引物的长度(以碱基数计算)
J+ —— 单价阳离子浓度

(2.4) DNA与表达蛋白之间分子量换算 
1 kb DNA = 333 amino acid ≈ 3.7 ′ 104 Da
10,000 Da Protein ≈ 270 bp DNA
30,000 Da Protein ≈ 810 bp DNA
50,000 Da Protein ≈ 2701 bp DNA
100,000 Da Protein ≈ 27 kb DNA