need explanations for all the answers Biochemistry section ll: (40 pts) Answer a

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need explanations for all the answers

Biochemistry

section ll: (40 pts) Answer all 4 of the questions. Show a work pure Give the you know is simple 1. 10 are trying observations. You may use a points) You to the sequence fa p most likely explanation for each of the following experi labeled diagram for your answer. ala as Ala Met and Leu as amino-termina an (a) The Sanger reagent (FDNB, fluorodinitrobenzene) ident wi gel electrophor the protein with beta residues, in roughly equal amounts oethanol, (b) your protein shows three bands as determine SDS apparent Mr of 18000, 22000 and 20000. After treatmento and 20000. has an the same technique reveals three bands with Mr of 18000 22000 the native protein (c) size-exclusion chromatography (gel filtration) indicate tein sequence apparent Mr of 60,000. Theres no custen present in Resent in the The only 2 amin, acids Correa

Explanation / Answer

Ans. A. One polypeptide chain has a single N-terminal and C-terminal residue.

So, presence of 3 different N-terminal residues (Ala, Met, Leu) indicates that the protein consists of 3 polypeptides- one with Met as N-terminal, one as Ala as N-terminal and one with Leu as N-terminal residue.

Presence of equal amount of N-terminal residues indicates that the ratio of the three polypeptides in the protein in 1:1:1. So, the exact number of polypeptides (subunits) in the protein can be 1 Met-subunit, 1 Ala-subunit and 1 Leu-subunit or in multiple of 1:1:1 ratio.

Ans, B. b-mercaptoethanol is used to separate two polypeptides linked together by a disulfide bond. No additional band formation after b-mercaptoethanol indicates that there no disulfide bond between two subunits of the protein.

However, it does not eliminate the chances of intra-polypeptide disulfide bond (a disulfide bond within a polypeptide chain) or presence of cysteine residues in the polypeptides because their reduction by b-mercaptoethanol does affect the number of bands.

Ans. C. It indicates that the protein consists of three subunits- one subunit of each polypeptides. So, the sum of Mw of three polypeptides is equal to 60000. If the number were in multiple of (1:1:1) ratio, say 2 polypeptides of each type, then the Mw would have also been multiple of Mw of individual polypeptides.    

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