Repetitive DNA Part 2 Flashcards
2 types of analytical ultracentrifugation
- equilibrium or bouyant density centrifugation
- sedimentation velocity centrifugation
two types of ultracentrifugation
- analytical
- preparative
analytical
- used to study the properties of molecules
preparative
- used to purify molecules by separating from other molecules so that their properties can be studied by other means
Equilibrium or bouyant density centrifugation
- high molecular weight DNA sheared and mixed with CsCl and a subjected to high g forces
- CsCl forms a gradient from highest density at the bottom to lowest density at the top
- DNA migrates to a position in the gradient where the density matches the density of the CsCl
what is formed in Equilibrium or bouyant density centrifugation
- a broad band is formed covering a range of fragments of different densities
Bouyant density is a function of
- G+C content
- not size
Higher G+C content
- higher density
if the satellite DNA has a GC content nearly the same as main GC content
- no satellite would be visible at all
sedimentation validity is a function of
- density
- size
- shape
how sedimentation velocity works
- put molecules on top of solution in centrifuge tube
- turn on centrifuge and measure rate of migration down the tube
large molecules sediment
- faster
what makes things sediment faster
- compact state
what makes things sediment slower
- extended state
How repetitive DNA can sometimes (but not always) be recognized as satellite DNA
- because of GC content that is different from the overall average GC content of DNA in the genome.
S values in complexes with subunits
- the S values of the subunits are not expected to add up to the S value of the entire complex.