Biochemistry Which of the following pentapeptides is expected to be the BEST dis
ID: 56835 • Letter: B
Question
Biochemistry
Which of the following pentapeptides is expected to be the BEST dissolved in water?
Select one:
a. NH2 - ser - pro- gly - ala- cys - asn - COOH
b. NH2 - tyr - thr - gly - ser - gln - asp - COOH
c. NH2 - ser - ala - gly - phe - gln - asp - COOH
d. NH2 - gly - leu - phe - val - ser - gly - COOH
A protein has a molecular mass of 200 kDa as determined by gel filtration (=native molecular weight). When separated by SDS-PAGE (without a reducing agent present) only one polypeptide appeared with a mass corresponding to 100 kDa. When determined by SDS-PAGE in combination with a reducing agent (DTT) exactly two polypeptides appeared of sizes 40 and 60 kDa. What is the correct structure of the native protein?
Select one:
a. The native protein is made of one 40 kDA and one 60 kDA polypeptides
b. The native protein is made of two 100 kDa polypeptides
c. The native protein is made of two 40 kDA and two 60 kDA polypeptides
d. The native protein is made of four polypeptides - two 100 kDa polypeptides, one 40 kDA and one 60 kDA polypeptides
e. None of the answers is correct.
Explanation / Answer
The pentapeptide that is made of completely hydrophobic amino acids is not soluble in water. The peptide that contains 25 % charged amino acids and 25 % hydrophobic amino acids will be soluble in water.
Hence, the correct among the following is option b.
Polyacrylamide gel electrophoresis (PAGE) is the analytical technique, which is used to separate and characterize the proteins. The sodium dodecyl sulfate is an amphipathic detergent that binds non-covalently to a protein. SDS causes protein to denature and dissociate from each other. The bands are not identifiable as separate bands as they are formed of equal size. When these bands are further subjected to reducing agent they formed two bands of 60 and 40 KDa.
Hence, the correct answer among the following is option b.
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