Biomolecules (B) question bank (Biology)

Camels have three different sub-classes of $\operatorname{IgG}(\operatorname{IgG} 1, \operatorname{IgG} 2$ and $\operatorname{IgG} 3)$, of which IgG2 and IgG3 are structurally different from the human IgG. A researcher purified camel IgG1 and IgG3, and carried out gel electrophoresis that separates polypeptides based on their molecular size. An IgG antibody purified from human serum is electrophoresed on the same gel. A schematic of the observed band pattern on the gel is shown in the figure, wherein lane M depicts molecular weight marker positions $(\mathrm{kDa}) ; \mathrm{R}$ : samples were treated with a reducing agent (such as $\beta$-mercaptoethanol); NR: no reducing agent was used. Based on this information, the correct structure of camel IgG3 is ______.

The amino acid sequence of an unknown peptide can be determined using a series of proteolytic digestions. An eight-mer peptide contains 1 alanine (ALA), 2 arginines (ARG), 1 methionine (MET), 1 serine (SER), 1 tyrosine (TYR) and 2 valines (VAL) with ALA at the N-terminus and VAL at the C-terminus. This peptide was digested with trypsin (cleaves the peptide bond C-terminus to a LYS or ARG) and chymotrypsin (cleaves the peptide bond N-terminus to an aromatic amino acid) in two separate reactions. The amino acid composition of each of the fragments obtained is given below:
Trypsin digestion: fragment 1: SER, ALA, ARG; fragment 2: VAL; fragment 3: TYR, ARG, MET, VAL

Chymotrypsin digestion: fragment 1: VAL, ARG, ALA, SER; fragment 2: VAL, TYR, ARG, MET
The correct amino acid sequence of the eight-mer peptide is: