Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) is a method used to separate proteins by size. It involves extracting proteins from a sample, solubilizing and denaturing the proteins using SDS detergent and heat, separating the proteins on a polyacrylamide gel based on their size and charge, and staining proteins for visualization and analysis. Smaller proteins move faster through the gel towards the positive electrode. SDS-PAGE allows determination of protein size, identification, purity, and quantification.

2.  Sodium dodecylsulphate-polyacrylamide
gel electrophoresis
 Method for separation of proteins according
to their molecular weight

3.  Determine protein size
 Identify protein
 Determine sample purity
 Identify existence of disulfide bonds
 Quantify amounts of protein

4.  Extract Protein
 Solubilize and Denature Protein
 Separate Proteins on a gel
 Stain proteins (visualization)
 Analyze and interpret results

5.  Negatively charged proteins move to positive
electrode
 Smaller proteins move faster
 Proteins separate by size
-
+
s-s
SDS, heat
proteins with
SDS

6. • SDS (Sodium Dodecyl
Sulfate) detergent
–solubilizes and
denatures proteins
–negative charge to
proteins
• Heat denatures proteins
O S O
O
O
-
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH3
SDS

7.  Negatively charged proteins move towards
the positive pole
 Migration of proteins:
-directly proportional to the overall charge of
proteins.
- inversely proportional to protein size
(molecular weight)

8.  The gels typically consist of acrylamide, bisacrylamide,
the optional denaturant (SDS or urea), and a buffer
with an adjusted pH.
 The solution may be degassed under a vacuum to
prevent the formation of air bubbles during
polymerization
 Alternatively, butanol may be added to the resolving
gel (for proteins) after it is poured, as butanol removes
bubbles and makes the surface smooth.

9.  A source of free radicals and a stabilizer, such
as ammonium persulfate and TEMED are added to
initiate polymerization
 The polymerization reaction creates a gel because of
the added bisacrylamide, which can form cross-links
between two polyacrylamide molecules
 The ratio of bisacrylamide to acrylamide can be varied
for special purposes, but is generally about 1 part in 35.
 The acrylamide concentration of the gel can also be
varied, generally in the range from 5% to 25%.

10.  Lower percentage gels are better for resolving very
high molecular weight molecules, while much
higher percentages are needed to resolve smaller
proteins.

12.  Acrylamide gel: tight matrix
 Ideal for protein separation
 Smaller pore size than agarose
 Proteins much smaller than intact
chromosonal DNA
 average amino acid = 110 Da

16. Versatility in Identification
Low Cost to Use
Accuracy of Results

17.  Electrophorresis Has Limited Sample
Analysis
 Electrophoresis Measurements Are Not
Precise
 Only Certain Molecules Can Be Visualized
 Electrophoresis is Low Throughput