4. SDS-PAGE ( sodium dodecylsulphate-
polyacrylamide gel electrophoresis)
The purpose of this method is to
separate proteins according to their size,
and no other physical feature
And it is a step in Western blot
5. The gel (matrix) itself is composed of either
agarose or polyacrylamide.
Polyacrylamide is a cross-linked polymer of
acrylamide.
Acrylamide is a potent neurotoxin and should be
handled with care!
6. Have smaller pores than agarose,
therefore high degree of resolving power.
Can separate DNA fragments which
range in size from 10-500 bp.
Polyacrylamide gel electrophoresis is also
used to separate protein molecules.
7.
8. Temed
Cross-linked polyacrylamide
gels are formed from the
polymerisation of acrylamide
monomer in the presence of
smaller amounts of N,N’-
methylenebisacrylamide (bis-
acrylamide)
Bisacrylamide is the most
frequently used cross linking
agent for polyacrylamide gels
9. SDS (sodium dodecyl sulfate) is a
detergent that can dissolve hydrophobic
molecules but also has a negative
charge (sulfate) attached to it.
If SDS is added to proteins, they will be
soluablized by the detergent, plus all
the proteins will be covered with many
negative charges.
10. Now we are ready to focus on the second half - PAGE.
12. So much SDS binds to proteins that the negative
charge on the SDS drowns out any net charge on
protein side chains
In the presence of SDS all proteins have uniform
shape and charge per unit length
SDS nonpolar chains arrange themselves on
proteins and destroy secondary tertiary and
quarternary structrure
13. DC Power Source, Reservoir/Tank, Glass Plates,
Spacers, and Combs
Support medium
Gel (Polyacrylamide)
Buffer System
High Buffer Capacity
Molecules to be separated
Proteins
Nucleic Acids
14. Prepare polyacrylamide gels
Add diluted samples to the sample
buffer
Heat to 95°C for 4 minutes
Load the samples onto polyacrylamide
gel
Run at 200 volts for 30-40 minutes
Stain
15. Mix ingredients GENTLY! in the order shown
above, ensuring no air bubbles form.
Pour into glass plate assembly CAREFULLY.
Overlay gel with isopropanol to ensure a
flat surface and to exclude air.
Wash off isopropanol with water after gel has
set (+15 min).
16.
17. Tris buffer to provide appropriate pH
SDS (sodium dodecyl sulphate) detergent to
dissolve proteins and give them a negative
charge
Glycerol to make samples sink into wells
Bromophenol Blue dye to visualize
samples
Heat to 95°C for 4 minutes
18. Run at 200 volts for 30-40 minutes
Running Buffer, pH 8.3
Tris Base 12.0 g
Glycine 57.6 g
SDS 4.0 g
distilled water to 4 liter
19.
20. Chemical stains detect proteins based on
differential binding of the stain by the protein
molecules and the gel matrix.
They are nonspecific in action, detecting proteins
without regard to their individual identities.
The important characteristics for a useful stain
are: low background, high sensitivity, large linear
range and ease of use.
21. smaller proteins
will move through
the gel faster
while larger
proteins move at
a slower pace
22. Step by Step Instructions on how to assemble the polyacrylamide gel
apparatus
Editor's Notes
SDS-PAGE
Denature protein(s) 100ºC, heat in presence of 1% SDS and 0.1M MCE
This gives proteins uniform shape and constant q/m
SDS binds denature protein 1.4g SDS/g Protein primarily through hydrophobic interactions with its long C12 tail, the SO4 head group decorates the protien with negative charges to give proteins constant q/m
Thus, in an SDS-PAGE experiment electrophoretic mobility depends primarily on size, m. wt., since q/m and shape are essentially equal.
? Small molecules have a greater mobility than large molecules due to?
A- sieving effect of the gel matrix
? Because
A- all proteins under the same acceleration by E.
Thus SDS-page is used to separate proteins by their molecular weight, identify proteins by their molecular weight or estimate an unknown protein’s molecular weight. The latter is done by plotting log MWT for some standard proteins of known molecular weight, run at the same time in the same gel , versus their relative mobility (*distance traveled into the gel relative to a dye front for instance). This technique works for proteins and protein subunits 10,000 – 200,000 mwt.
Apparatus- vertical, vertical minis, tube and horizontal or flatbed design
Two electrodes [anode (+) and cathode (-)] in conductive buffer:
2e- + 2H2O → 2OH- + H2↑H2O → 2H+ + ½ O2↑ + 2e-
HA + OH- → A- + H2OH+ + A- → HA
Apply equal and constant voltage on all cross-sectional areas of solid support. Electric field (volts/cm)
Ohm’s law (E = IR) voltage is a function of current (I) and resistance (R) and since electrophoresis apparatus and buffers give a constant resistence, current is often used to define the voltage requirements
?What carries the current?
A- Proteins and Nuclein Acids and all ions in solution
Therefore we perform GE experiments in low ionic strenth buffer 0.05 – 0.15 M so thecurrent is not swamped with small molecule ions such that the proteins experimnce very little of the current and at pH 9 where most porteins have a negative charge and will migrate toward the anode
(16 picograms = 16 × 10 -12 grams) in order to be detected. The gel has been stained with Coomassie brilliant blue.