WBR0340
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| Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Immunology |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::In order to study cellular responses, a student exposes two groups of mice to an influenza virus infection: A control group with intact bone marrow and another group with completely ablated bone marrow. The student observes that in the control group, concentrations of an intracellular protein (Protein A) in muscle cells rise in parallel with the intracellular activity of 2'-5′ oligoadenylate synthetase and the serum concentration of IFN-α/β. In contrast, the influenza viral load is much more elevated in the group with the ablated bone marrow, while no rise in protein A concentrations is observed. Which of the following is the most likely function of protein A?]] |
| Answer A | AnswerA::Phospholipase |
| Answer A Explanation | AnswerAExp::Phospholipases are membrane proteins that hydrolyzes phospholipids. Interferons do not induce an antiviral response by activating phospholipases. |
| Answer B | AnswerB::Endonuclease |
| Answer B Explanation | AnswerBExp::Endonucleases are enzymes that recognize specific base sequences in DNA and cleave a polynucleotide chain. Interferons do not induce an antiviral response by activating endonucleases. |
| Answer C | AnswerC::Protease |
| Answer C Explanation | AnswerCExp::Proteases hydrolyze the peptide bonds of amino acids. Interferons do not induce an antiviral response by activating proteases. |
| Answer D | AnswerD::Deoxyribonuclease |
| Answer D Explanation | AnswerDExp::Deoxyribonucleases are endonucleases that catalyze the cleavage of phosphodiester bonds in the DNA backbone. Interferons do not induce an antiviral response by activating deoxyribonuclease. |
| Answer E | AnswerE::Ribonuclease |
| Answer E Explanation | AnswerEExp::Ribonucleases are enzymes that catalyze the degradation of RNA. Interferons induce an antiviral state within the target cells by activating RNase L, a ribonuclease which breaks down viral RNA. |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation::Interferons are a diverse family of proteins involved in cell growth, antiviral defense, and immune activation. Type I interferons, which are products of the direct response to viral infection, consist of IFN-α, produced mainly by the immune system, and IFN-β, produced by most cell types. Type II interferons, which consists of IFN-γ, are usually produced following the recognition of infected cells by T-lymphocytes. IFNs induce an antiviral state within target cells by activating RNase L, a ribonuclease, which breaks down viral RNA and inhibits viral replication. RNase L is activated by 2'-5′ oligoadenylate synthetases, which are a group of enzymes induced by an interferon binding to its receptor. Educational Objective: Interferons induce an antiviral state within the target cells by activating RNase L, a ribonuclease which breaks down viral RNA. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Interferon, WBRKeyword::Ribonuclease, WBRKeyword::RNAse L, WBRKeyword::Enzyme, WBRKeyword::Influenza, WBRKeyword::Bone marrow, WBRKeyword::Experiment |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |