Fever after death of gram-negative bacteria is caused by release of:

A. Guanine: Guanine pairs with cytosine in both DNA and RNA through three hydrogen bonds. It does not pair with uracil, as the chemical structure of uracil does not allow stable hydrogen bonding with guanine.

B. Adenine: In RNA, uracil replaces thymine and forms two hydrogen bonds with adenine. This base-pairing maintains the complementary structure needed for RNA transcription and folding, ensuring accurate coding during protein synthesis.

C. Thymine: Thymine is found only in DNA and pairs with adenine. In RNA, uracil substitutes for thymine, so thymine does not pair with uracil.

D. Cytosine: Cytosine pairs with guanine via three hydrogen bonds in both DNA and RNA. Cytosine does not pair with uracil because the hydrogen bonding does not match the structural requirements.

When a virus enters a host cell, it hijacks the host's cellular machinery to replicate itself. Viral genes direct the host cell to transcribe and translate viral proteins instead of its own normal proteins. This redirection alters the host’s metabolic and genetic activities, often shutting down regular cellular processes. The host cell becomes a “viral factory,” producing viral components that are then assembled into new virions. This process can damage or kill the host cell, depending on the type of virus and replication strategy, and is a defining characteristic of viral infections, distinguishing them from non-infectious intracellular activities.