Buoyant density

Deoxyribonucleic acid (from plasmids). Purified by two buoyant density ultracentrifugations using ethidium bromide-CsCl. The ethidium bromide was extracted with Et20 and the DNA was dialysed against buffered EDTA and lyophilised. [Marmur and Doty J Mol Biol 5 109 1962 Guerry et al. J Bacteriol II6 1064 1973.] See p. 504. 

Not only the melting temperature of DNA but also its density in solution is dependent on relative G C content. G C-rich DNA has a significantly higher density than A T-rich DNA. Furthermore, a linear relationship exists between the buoyant densities of DNA from different sources and their G C content... 

B = Ratio of buoyant density of the biofilm to the buoyant density... 

As a consequence of high osmolarity, macromolecules or organelles are dehydrated resulting in altered sedimentation behavior thus, different buoyant densities for nucleic acids and mitochondria are observed in different density gradient media, as illustrated in Table 5.3. Data of some density gradient media are given in Table 5.4. 

Table 5.3. Buoyant density of mitochondria and DNA from Micrococcus luteus (G+C 71%), dependent on the applied density gradient medium...

In a second study by the same group phagocytic vacuoles were prepared from PMNs which had been exposed to opsonized oil particles. The phagocytic vesicles could be collected because of the distinctive buoyant density in a discontinuous gradient of sucrose of the oil within phagocytic vacuole. The effects of CN", of chelators, and of EDTA on the appearance of activity in the phagocytic vacuoles... 

What is their volume If the mass of a bacterial ribosome is 2.7 x 106 daltons, what is its apparent density (divide mass by volume) Experimentally the buoyant density of bacterial ribosomes in a cesium chloride gradient (Chapter 5) is about 1.6 g/crn3. How can this difference be explained If eukaryotic ribosomes are 1.17 times larger than bacterial ribosomes in linear dimensions, what is the volume of a eukaryotic ribosome ... 

The small particles of plasma lipoprotein, which carry triacylglycerols, can be separated according to their buoyant densities by centrifugation. They have been classified into five groups of increasing density but smaller size as chylomicrons, very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL), low density (LDL), and high density lipoproteins (HDL) (Table 21-1 and Fig. 21-2). Each lipoprotein particle contains one or more apolipoproteins (Table 21-2), whose sizes vary from the enormous 4536-residue apoB-100 to apoC-II and apoC-III, each of which contains just 79 residues73 and the 57-residue apoC-I.7b... 

Template DNA for the production of hybridization probes must be pure Standard methods, such as dye-buoyant density ultracentnfugation, generate acceptable products. Ethidium bromide and cesium chloride are removed prior to use of the DNA (4)... 

Hillyer, G.V. (1974) Buoyant density and thermal denaturation profiles of schistosome DNA. Journal of Parasitology 60, 725-727. 

Bakken, L.R. and Olsen, R.A., 1983. Buoyant densities and dry-matter contents of microorganisms conversion of a measured biovolume into biomass. Appl. Environ. Microbiol., 45 1188-1195. 

Double-helical DNA in solution can undergo strand separation or dena-turation as a consequence of extremes of pH, heat, or exposure to chemicals such as urea or amides. Decrease in viscosity, increase in absorbance at 260 nm (hyperchromic effect), decrease in buoyant density, or negative optical rotation indicates denaturation of DNA. The denaturation process disrupts only noncovalent interactions between the two strands of DNA. Since G-C base pairs are held together by three hydrogen bonds in contrast to two for an A-T base pair, A-T rich DNA is easily denatured compared to G-C rich DNA (Figure 6.3). Electron microscopy can detect these A-T-rich regions in a DNA molecule since they form bubblelike structures. Hence the temperature of melting (Tm) of DNA increases in a linear fashion with... 

Buoyant density in CsCl (g/ml) % G + C from buoyant density Thermal denaturation (°C) % G + C Mean length 0 m)... 

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