In bacteriophage replication (lytic cycle), the virion parts self-assemble into mature phages only after both the phage genome and the structural proteins have been synthesized. Which prerequisite(s) trigger assembly?

Introduction / Context:
Bacteriophage (phage) replication proceeds through ordered stages: adsorption, injection, replication of nucleic acid, synthesis of capsid and tail proteins, assembly (maturation), and lysis. The question asks what must be synthesized before components begin to assemble into complete virions. Understanding this sequence clarifies how phages coordinate genome packaging with capsid formation.

Given Data / Assumptions:

• The context is a lytic phage infection of a bacterial host.
• Phage genes drive host machinery to produce viral nucleic acid and structural proteins.
• Assembly (head, tail, tail fibers) requires both the genome and capsid/tail subunits to be available.

Concept / Approach:
Phage assembly is a self-organizing process guided by scaffolding proteins and precise protein–protein interactions. Genome packaging motors load the replicated nucleic acid into preformed heads. Thus, assembly requires two categories of inputs: the replicated nucleic acid (DNA or RNA, depending on the phage) and the synthesized structural proteins (capsomers, tail proteins, base plates). Mere availability of amino acids or genome alone is insufficient.

Step-by-Step Solution:
Recognize that structural proteins form procapsids and tails via ordered pathways.Note that genome replication produces many copies of phage nucleic acid.Assembly initiates once both structural subunits and the nucleic acid are present.Genome is packaged into the head; tails and fibers attach to complete virions.Cells lyse to release mature progeny.

Verification / Alternative check:
Pulse-chase experiments show a time lag: first nucleic acid and protein synthesis, then sudden appearance of infectious particles (one-step growth curve), confirming assembly occurs after both categories are synthesized.

Why Other Options Are Wrong:
Structural proteins only: without genomes, empty heads cannot produce infectious phages.Phage nucleic acid only: genome without capsids cannot mature or survive outside the cell.Free amino acids only: building blocks alone do not trigger assembly.

Common Pitfalls:
Confusing translation of proteins with assembly, or assuming packaging can begin before structural scaffolds exist.

Final Answer:
Both (a) and (b)