Molecular separations Flashcards
reasons for biomolecule purification
study their properties
analyse distribution/ abundance
commercial/ medical use
synthetic biomolecules
incomplete reaction products resembling final product
2 main techniques for purification
electrophoresis
chromatography
relative centrifuge force
centrifugal force/ g force
microfuge
low speed
ultracentrifuge
high speed
isolation of protein sources in blood/ bacteria
centrifuge
isolation of protein sources in organs/ tissues
homogenisation
cell g force
3000g
organelle g force
20000g
protein g force
100000g
chromatography factors
size
charge
affinity
factors affecting affinity for stationary phase
charge interactions (ion exchange chromatography)
hydrophobicity (reverse phase/ hydrophobic interaction)
size (gel filtration/ size exclusion)
specific binding (affinity chromatography)
gel filtration
porous beads in which size affects distance travelled
ion exchange chromatography
elution via salt conc ^ competing for charge interactions
protein rich in charged residues
reverse phase chromatography
eluted by polarity reversal of solution via solvents
affinity chromatography
addition of free binding partner
immobilised metal affinity chromatography
- Histag addition
- elution
*imidazole addition
histag
6-10 histidine residues at N/C terminus end
imidazole side chain specifically binding to metals
addition of histag
addition of DNA coding for histag into natural DNA
bacteria produce protein
histidine characteristic
heteroaromatic
- charged amine group
histag elution
imidazole addition elutes
gradient/ step addition
step elution
all bound molecules elute at once
gradient elution
separates if different types bound
gel electrophoresis gel function
convection current prevention so molecules move as a band, not dispersed
gel pore size effect on gel electrophoresis
control macromolecule migration speed
PAGE (polyacrylamide gel electrophoresis)
acrylamide polymers cross-linked w methylene bisacrylamide
acrylamide polymer percentage effect
changes pore size
pH of PAGE
> 8 therefore proteins are mostly negatively charged
NATIVE-PAGE
Proteins separated by size, shape and charge
colourless protein reveal in NATIVE-PAGE
blue-stain
SDS
sodium dodecyl sulphate
*lauryl sulphate in shampoo
SDS process
denatures proteins/ adds negative charge
shape/charge independent
heated w SDS/ mercapto-ethanol to disrupt disulfide bonds and denature
SDS-PAGE
separation by protein size only
mercapto ethanol and heated to 95 degrees celcius denature
depends on pore size
marker proteins often used
pore size proportion to molecular weight in SDS-PAGE
pore size proportional to log(MW)
IEF
Iso-Electric Focussing
IEF summary
Native-page carried out on pH gradient caused by ampholytes
ampholytes
large polyions
equilibrium technique IEF
proteins stop when they reach an isoelectric point
what does IEF identify
proteins, their isomers and chemical modification
2D Gel electrophoresis
IEF in tubular gels as first dimension, SDS page in second dimension
isoelectric point/ pI
pH at which a particular molecule carries no net electrical charge
what does 2D gel electrophoresis separate by?
size and pI
DNA gel electrophoresis visualisation
UV light and fluorescent dyes
DNA gel electrophoresis
small DNA fragments separated at high res via acrylamide gels in sequencing
larger fragements have larger pore gels
fixed negative charge density