Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
Which of the following statements are CORRECT when a protein sequence database is
searched using the BLAST algorithm?
P. A larger E-value indicates higher sequence similarity
Q. E-value < 10-10 indicates sequence homology
R. A higher BLAST score indicates higher sequence similarity
S. E-value > 10'° indicates sequence homology
Options:
(A) P, and R onl
(C) P. R and S only
5) P and only
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2019 Q.39)**
**1. Governing Concept**:
- **Topic**: Immunology & Cell-Mediated Immunity
- Evaluating cytotoxic cell activation:
- Natural Killer (NK) cells express inhibitory receptors (KIRs) that bind self **MHC class I**. When target cells downregulate MHC-I ("missing self" hypothesis), the inhibitory signal is relieved, triggering NK-cell-mediated perforin/granzyme degranulation and lysis.
- Cytotoxic CD8+ T lymphocytes require foreign peptide presentation on MHC class I to activate cytotoxicity.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: CD8+ T cells require MHC-I for activation.
- **Option (B) is CORRECT**: Accurately differentiates MHC-I restriction between CD8+ T-cells and NK missing-self recognition.
- **Option (C) is INCORRECT**: Distorts receptor signaling.
- **Option (D) is INCORRECT**: Inverted activation criteria.
**3. Final Answer**:
- **Correct Choice**: **B**
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