3. The five major proteins found in milk are shown in table 1 below with their p
ID: 212249 • Letter: 3
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3. The five major proteins found in milk are shown in table 1 below with their pl and molecular weights in kDa Table #1. Protein a-casein B-casein pl* 4.8 5.1 6.2 5.5 4.5 MW (kDa)* K-casein B-lactoglobulin a-lactoalbumin 23 24 19 18.4 14 The electrophoresis gel in Figure 1, shown in the following page was obtained from the separation of proteins from reconstituted skim milk and milk whey. Use the results found with the SDS-PAGE to respond the following questions (a) Using the information provided in Table # 1 and the tesults og the SDSPAGE, identify the proteins present in lanes 3, 4, 5(& 6 both have the same protein) and 7. Explain your reasoning (b) What are the major differences between the results obtained for the sample treated with 2-mercatoethanol (lane 2) vs the sample NOT treated with 2-mercaptoethanol (lane 1)? (c) How can you explain the differences in the results observed between the samples in lanes 1 & 21?Explanation / Answer
A. The proteins are dependent upon the molecular weight in SDS-page wether the lane is treated with 2 mercaptoethanol or not as you are seeing in lane 1 (the sample is not treated with 2mercaptoethanol ), in lane 2 it is treated with 2mercaptoethanol.
B. The major difference between while using 2-mercaptoethanol in SDS page and by not treating it with 2-mercaptoethanol in SDS-page:
1. By Treating with 2-mercaptoethanol:
a. 2- mercaptoethanol is suitable for reducing protein disulfide bonds and they are mainly used in the sample buffer for SDS-page, it determines the molecular weight, mainly it is used as it denatures the protein of interest.In most proteins, the binding of SDS to the polypeptide chain imparts an even distribution of charge per unit mass, thereby resulting in the fractionation by approximate size during SDS-page, it acts as a catalyst, i.e. in lane 2
SDS-PAGE of proteins that have been reduced with mercaptoethanol is useful for measuring the monomer molecular weight. Reduction of the disulfide bonds is important for allowing the protein to become completely unfolded so that it migrates properly for its molecular weight.
2. By not treating with 2-mercaptoethanol:
It will not reduce and the sample without treating with 2-mercaptoethanol will not denature the protein and thereby molecular weight will not be measureable.i.e in lane 1.
C. The difference between the lane 1 and lane 2 is that in lane 1 the milk sample was not treated with 2-mercaptoethanol and therefore they are not reduced and they donot measure the molecular weight using SDS-page and the proteins are not denatured and in lane 2 the milk sample was treated with 2 mercaptoethanol therefore they are reduced and measure the molecular weight and they act as a catalyst also known as a "Tracking dye".
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