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Convert Mass into Volume¶
This page will help you convert the mass of a macromolecule into a diameter in a micrograph.
Denisities- Protein density is 0.728 ml/g
- Y. Harpaz, M. Gerstein and C. Chothia, "Volume changes on protein folding", Structure 2 (1994), pp. 641–649.
- RNA density is 0.577 ml/g
- N.R. Voss and M. Gerstein, "Calculation of Standard Atomic Volumes for RNA and Comparison with Proteins: RNA is Packed More Tightly", JMB v346#2 (2005), pp. 477-492.
- 1 Å<sup>3</sup>/Da = NA×10−24 = 0.6022 ml/g
- Protein density is 1.209 Å<sup>3</sup>/Da
- RNA density is 0.958 Å<sup>3</sup>/Da
- given macromolecule mass, m in Daltons, macromolecule protein mass, m<sub>p</sub> in Daltons, and macromolecule RNA mass, m<sub>r</sub> in Daltons;
- 4/3 π r^3 = m<sub>p</sub> * 1.209 + m<sub>r</sub> * 0.958
- 2/3 π r^3 = m<sub>p</sub> * 1.209 + m<sub>r</sub> * 0.958
- Mass:
- m<sub>p</sub> = 400,000
- m<sub>r</sub> = 0
- 4/3 π r^3 = 400,000 * 1.209
- r = (400,000 * 1.209 * 3 / 4 / π)^(1/3) = 48.7 Å
- i.e. a diameter of 97.4 Å
- 2/3 π r^3 = 400,000 * 1.209
- r = (400,000 * 1.209 * 3 / 2 / π)^(1/3) = 61.3 Å
- i.e. a diameter of 122.7 Å
Updated by Neil Voss over 14 years ago · 4 revisions