Chapter 43, Problem 1IQ

Briefly describe the insect defense system against infecting RNA viruses.

Why does this system not attack the RNA of normal insect cells?

Summary Introduction

To explain: Insect defense system against infecting RNA viruses.

Introduction: The defense system in insects is innate immunity. Like humans, insect is also prone to infectious agents like bacteria, virus, parasites, and fungi on a daily basis. To protect themselves from the pathogens, the insects develop a potential immune system. The innate immune system of insects is divided into two types, namely cellular immunity and systemic immunity.

Explanation of Solution

Insects, when exposed to infectious agents, synthesize enormous amounts of antimicrobial peptides to fight with that infection. One such peptide is Dicer-2 enzyme, which recognizes the double-stranded viral RNA and cuts them into short fragments. The Argo protein complex, known to involve in gene silencing, binds with the RNA fragment, which in turn binds with the complementary viral mRNA molecule. The Argo complex prevents the translation by cleaving the viral mRNA.

Summary Introduction

To explain: Insect defense system’s inability to attack the normal insect cells.

Explanation of Solution

The RNA molecules in eukaryotic cells are generally single stranded. However, the viral RNA is double-stranded. Therefore, the Dicer enzyme cannot recognize the single-stranded host RNA. The difference in the RNA strands made the insect’s immune system to distinguish between the self and non-self cells.