This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Endogenous Pathway of Antigen Processing and Presentation”.
1. Where are endogenous proteins processed?
a) Cytosol
b) Endosomes
c) Cytoplasm
d) Lysosomes
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Explanation: Endogenous proteins are the proteins that exist as components of living cells. They are also called as tissue proteins. These proteins are processed in cytosol or in secretory vesicles. Cytosol is the interior portion of the cell which is in liquid form. The endogenous proteins float in the cytosol. On the other hand, secretory vesicles are little packages in which the proteins are transported. These proteins act as mediators in order to carry out the processing and presentation of antigens.
2. What are the antigens that are involved in autoimmune disease pathogenesis called?
a) Non-self-antigens
b) Self-antigens
c) Autoimmune antigens
d) Pathogenic antigens
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Explanation: Antigens involved in autoimmune disease pathogenesis are called self-antigens. These antigens are independent and produce immune responses as well as stimulate the functioning of auto antibodies. These self-antigens are cellular proteins, peptides and enzymes complexes. These antigens play an important role in peripheral tolerance mechanisms, T and B cell apoptosis, etc.
3. Endogenous antigens are associated with molecules in order to activate which of the following cells?
a) Class II MHC
b) Peptide molecules
c) Class I MHC
d) Antigen presenting cells
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Explanation: Endogenous antigens are associated with MHC class I molecules and play a very important role in activating cytotoxic CD8+ T cells. This activation leads to killing of infected cells as well as tumour cells. MHC class I molecules are very important as they are the base of immune recognition, its response and regulation in the body. These mechanisms can possibly take place only if MHC class I molecules bind to antigen peptides in order to from antigen peptide-MHC class I molecular complexes.
4. What is the full form of TAP proteins?
a) Transporters associated with Antibody Processing
b) Transporters associated with Antigen Presentation
c) Transporters associated with Antibody Presentation
d) Transporters associated with Antigen Processing
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Explanation: TAP proteins are very important in endogenous pathway of antigens for their processing. TAP stands for Transporters associated with Antigen Processing. These proteins attract the endogenous antigens to bind to them. TAP proteins help in transportation of amino acid antigen peptides to the endoplasmic reticulum (ER). The antigen polypeptide binds to the antigen-binding peptide groove of the MHC class I molecule assembled by the endoplasmic reticulum to form an antigen peptide-MHC I-like molecular complex.
5. Which of the following molecules bind to antigen peptide-MHC class I complex?
a) Calnexin and Tapasin
b) Tapasin and Calreticulin
c) Calreticulin and Calnexin
d) Proteasome and Calnexin
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Explanation: Tapasin and Calreticulin are the molecules bind to antigen peptide-MHC class I complexes. Tapasin forms a bridge between TAP proteins with the class I MHC molecules and increases steady state levels of TAP proteins in order to allow more peptides to be translocated in the endoplasmic reticulum (ER). On the other hand, Calreticulin prevents lodging of any other foreign peptides. These molecules are localised to Endoplasmic Reticulum (ER) where it functions as chaperone and regulates the cellular processes.
6. Which of the following is NOT the lysine residue of Ubiquitin?
a) K6
b) K11
c) K12
d) K27
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Explanation: Ubiquitin has a total of seven lysine residues which are as follows- K6, K11. K27, K29, K33, K48, K63 and M1. Ubiquitin is an important molecule that acts as a transporter and controller. It targets the proteins to proteasome which enhances the cytosolic protein degradation. In other words, the proteins get inactivated when they get targeted by Ubiquitin. This inactivation of proteins by ubiquitin is known as ubiquitination.
7. Which is the correct order of activities showcased by endogenous antigens?
i) Peptide binding to MHC Class I
ii) Transport to Endoplasmic Reticulum
iii) Generation of Peptide from proteolysis
a) i—ii—iii
b) iii—ii—i
c) ii—iii—i
d) i—iii—ii
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Explanation: Processing of endogenous antigens involve major 3 activities. In the first activity, peptides are generated. This takes place via proteolysis as proteins are targeted in order to combine with ubiquitin. Once the ubiquitin-protein complex is formed, it gets degraded by proteosome. These proteosomes generate the required peptides which can further bind to MHC class I. The second step involves transport of these peptides into the endoplasmic reticulum via TAP proteins. The third and final step involves binding of peptide to MHC class I mediated by tapasin and calreticulin.
8. The functional peptide transporter is a heterodimer consisting of the two subunits of TAP proteins namely TAP1 and TAP2.
a) True
b) False
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Explanation: TAP proteins (Transporters associated with Antigen Processing) consists of main two subunits TAP1 and TAP2. These subunits act as heterodimers in the membrane of Endoplasmic Reticulum to facilitate selective transport of peptides from cytoplasm into the lumen of Endoplasmic Reticulum. The transport of peptides is functioned by TAP pumps which help in transportation of these peptides with a length of 8-15 amino acids.
9. Which chaperone protein binds to α-chain of Class I MHC molecules to enhance their binding with antigens?
a) Heat shock proteins
b) Calnexin
c) Tapasin
d) Calreticulin
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Explanation: Calnexin is the protein chaperone that binds to class I MHC molecules to enhance their binding with antigens. This chaperone protects the MHC class I molecule from degrading while travelling to the antigens. It also ensures the quality of proteins as well as assist the proper folding of proteins.
10. Which of the following are the non-self-protein antigens that are involved in endogenous pathway of antigen processing and presemtation?
a) Tumor antigens
b) Viral antigens
c) Lysosomal antigens
d) Proteosome antigens
View Answer
Explanation: Endogenous antigens are derived from proteins produced inside the cell/these include self-proteins antigens (e.g., tumor antigens) as well as non-self-proteins antigens (e.g., viral antigens). These viral antigens are degraded into peptides by proteosomes. Virus antigens are associated with cells as they regulate the collection of adequate number of infected cells. Viral antigens also have multiple antigenic functions.
Sanfoundry Global Education & Learning Series – Immunology.
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