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Nucleic Acids and Protein Calculations Spectrophotometric Conversions
**This web page provides several useful tables of common biological constants and conversions. These include metric prefixes, spectrophotometiric conversions, agarose/polyacrylamide gel resolutions, etc. 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..
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 Conversions
| 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
| For 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 |
| For 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/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(%):Resolution of Linear DNA
| 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(%):Resolution of Protein
| Recommended
% Acrylamide |
Protein Size Range |
| 8 |
40-200 kDa |
| 10 |
21-100 kDa |
| 12 |
10-40 kDa |
Length/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. |
Standards
| 1. Average MW of dsDNA
base pair = 600. |
| 2. Average MW of ssDNA base =330. |
| 3. Average MW of RNA base =340. |
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