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Spectrophotometric conversions of protein and nucleic acids

 
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11/19/2013

Spectrophotometric conversions of protein and nucleic acids

This content provides several useful information of common biological constants and conversions. You can use these tables to aid your DNA/RNA/protein quantification, electrophoresis gel preparation, protein synthesis, calculating molecular mass and other research activities in molecular biology.

Tables include:

Metric Prefixes


Prefix Symbol Factor
kilo k 103
centi c 10-2
milli m 10-3
micro µ 10-6
nano n 10-9
pico p 10-12
femto f 10-15
atto a 10-18
zepto z 10-21
 

Spectrophotometric Conversion

1 A260 unit of double-stranded DNA=50 µg/ml
1 A260 unit of single-stranded DNA=33 µg/ml
1 A260 unit of single-stranded RNA=40 µg/ml


DNA Molar Conversions

1 µg of 1,000 bp DNA ≈ 1.52pmol(3.03pmol of ends)
1 µg of pBR322 DNA ≈ 0.36pmol DNA
1 pmol of 1,000 bp DNA ≈ 0.66 µg
1 pmol of pBR322 DNA ≈ 2.8 µg
 
pBR322DNA:（4,361bp）

Formulas for DNA Molar Conversions

dsDNA
To convert pmol to µg:
pmol × N × 660 pg/pmol × 1 µg/106pg = µg
To convert µg to pmol:
µg × 106pg/1 µg × pmol/660pg × 1/N = pmol
ssDNA
To convert pmol to µg:
pmol × N × 330 pg/pmol × 1µg/106pg = µg
To convert µg to pmol:
µg × 106pg/1 µg × pmol/330pg × 1/N = pmol
where N is the number of nucleotides and 330 pg/pmol is the average MW of a nucleotide
 


Protein Molar Conversions

100 pmol of 100 kDa protein = 10 µg
100 pmol of 50 kDa protein = 5 µg
100 pmol of 10 kDa protein = 1 µg
100 pmol of 1 kDa protein = 100 ng
 


Protein and DNA Conversions

1 kb DNA → 333 amino acids
  → 37 kDa protein
270 b DNA → 10 kDa protein
810 b DNA → 30 kDa protein
1.35 kb DNA → 50 kDa protein
2.7 kb DNA → 100 kDa protein
average MW of an amino acid ≈ 110 daltons
Dalton (Da) is an alternate name for the atomic mass unit, and kilodalton (kDa) is 1,000 daltons. Thus a protein with a mass of 64 kDa has a molecular weight of 64,000 grams per mole
 


Agarose Gel(%) of Linear DNA Resolution

Recommended % Agarose Optimum Resolution for Linear DNA
(Size of fragments in nucleotides;bp)
0.5 1,000-30,000
0.7 800-12,000
1.0 500-10,000
1.2 400-7,000
1.5 200-3,000
2.0 50-2,000
 


Polyacrylamide Gel(%) of Potein Resolution

Recommended % Acrylamide Protein Size Range
8 40-200 kDa
10 21-100 kDa
12 10-40 kDa
 


Length and M.W. of Common Nucleic Acids

Nucleic Acid Number of Nucleotides Molecular Weight
lambda DNA 48,502(dsDNA) 3.2 × 107
pBR322DNA 4,361(dsDNA) 2.8 × 106
28S rRNA 4,800 1.6 × 106
23S rRNA(E.coli) 2,900 1.0 × 106
18S rRNA 1,900 6.5 × 105
16S rRNA(E.coli) 1,500 5.1 × 105
5S rRNA(E.coli) 120 4.1 × 104
tRNA(E.coli) 75 2.5 × 104
*Molecular weights based on actual sequence.