Question

1. IgG molecule has a constant part (dubbed Fc) that is invariable for all immunoglobulins of a particular class, and a variable part that is unique for each IgG clone. Which part of the IgG molecule is NOT involved in binding to an antigen?

A. Fab
B. Fc
C. heavy chain

D. light chain

E. variable domain

2. Which statement is TRUE for protein synthesis in eukaryotes?
A. All proteins are initially synthesized with methionine at their C-terminus.
B. All proteins are initially synthesized with methionine at their N-terminus.
C. All proteins are initially synthesized with tryptophan at their C-terminus.
D. All proteins are initially synthesized with a multiple of 3 amino acids in their sequence.

E. None of the statements is true.

Answer 1

1)

B) Fc

Fc part of the IgG molecule is NOT involved in binding to an antigen. The protease papain cleaves antibody molecules into three fragments Two fragments which are identical contain the antigen-binding activity. These are the Fab fragments, which are antigens binding fragment. The Fab fragments correspond to the two identical arms of the antibody molecule, which contain the complete light chains paired with the VH and CH1 domains of the heavy chains. The other fragment is Fc contains no antigen-binding activity.

2)

Statement B All proteins are initially synthesized with methionine at their N-terminus.is TRUE for protein synthesis in eukaryotes.

Synthesis of a protein starts with the binding of ribosomal subunits and initiation factors to the mRNA. The initiation factor eIF₂ is bound to initiator t-RNA and not to other t-RNAs. Upon recognition of the initiation codon AUG, translation starts with the methionine that is bound to the initiator tRNA.