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. Table include:

• Metric prefixes
• Spectrophotometric conversion
• DNA molar conversions
• Formulas for DNA molar conversions
• Protein molar conversions
• Protein and DNA conversions
• Agarose gel (%) of linear DNA resolution
• Polyacrylamide gel (%) of protein resolution
• Length and molecular weight of nucleic acids

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

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.