1. IgG consists of ____________
a) A light chain and two heavy chains joined by a disulfide bond
b) Two light chains and a heavy chain joined by a disulfide bond
c) Two light chains and two heavy chains joined by a disulfide bond
d) Two light chains and two heavy chains joined by hydrogen bond
Explanation: IgG consists of 2 subunits including 2 heavy chains and 2 light chains.
2. Which of the following is a true statement?
a) IgG is involved in primary immune response
b) IgM is involved in primary immune response
c) IgG is involved only in secondary immune response
d) IgG and IgM both are involved in primary immune response
Explanation: IgG and IgM are involved in primary immune response.
3. The primary antibody of exocrine secretions is ____________
a) IgA
b) IgE
c) IgG
d) IgM
Explanation: IgA occurs in exocrine secretions and defends against bacteria cells and viruses.
4. Which of the following is not a feature of secondary immune respone to an antigen when compared to the first immune response to the same antigen?
a) Antibody is generated without T-cell help
b) Antibody is generated fast
c) Antibody produced has greater affinity for the antigen
d) Much antibody is produced
Explanation: The features of the secondary immune response are:
More antibodies are generated and the generation is fast.
Antibody produced has a greater affinity for the antigen.
5. Which of the following presents antigenic peptide to T-cells in order to initiate an adaptive immune response?
a) Plasma cell
b) Dendrite cell
c) Neutrophil
d) Epithelial cell
Explanation: Plasma cell is a fully differentiated B cell that produces antibody.
6. By what factor chymotrypsin enhances the rate of peptide bond hydrolysis?
a) 107
b) 108
c) At least 109
d) 106
Explanation: Chymotrypsin enhances the rate of peptide bond hydrolysis by a factor of at least 109.
7. The active site of chymotrypsin consists of a catalytic triad of which of the following amino acid residues?
a) Serine, histidine and aspartate
b) Serine, histidine and glutamate
c) Threonine, histidine and aspartate
d) Methionine, histidine and aspartate
Explanation: Aspartate holds the histidine side chain in the correct direction to accept proton from serine.
8. Which of the following statements are true about the reactions at the active center of chymotrypsin?
a) The aspartate residue gives an electron to histidine
b) The aspartate residue gives a proton to histidine
c) The aspartate residue keeps the histidine in the correct direction
d) A proton moves from the aspartate to serine to histidine in the catalytic triad of chymotrypsin
Explanation: Aspartate residue accepts a proton from serine.
9. The polypeptide chains in chymotrypsin are linked by __________
a) Hydrogen bonds
b) Ionic bonds
c) Disulfide bond
d) SH-SH bond
Explanation: The protein consists of three polypeptide chains linked by disulfide bonds.
10. Which of the following is false about chymotrypsin?
a) Hydrolytic cleavage of a peptide bond by chymotrypsin has two phases
b) It is activated in the presence of trypsin
c) It is synthesized in the thyroid gland
d) Polypeptide chains in chymotrypsin are linked by S-S bonds
Explanation: Chymotrypsin is synthesized in the pancreas.