Viral infection begins when the virus binds to the host cell. Following that, the virus has its viral genome enter the host cell through some manner. Now, some viruses like the bacteriophage we were just talking about actually inject their genome into the host, and you can see that happening right here in this image. And now, you might have a better understanding of why those bacteriophage have a more complex capsid than other viruses because that capsid actually has to function almost like a syringe injecting the genome which we see in green right here. Let me actually change my pen color so it's easier to see. Right there. So that viral genome gets injected into the host bacteria.
And this happens because of the surface of the bacteria cell inserts a portion into the actual exterior membrane of the bacteria, and then allows for the entry of the viral genome. Now this is a more complex process than many viruses employ. Many viruses get their genome inside the host cell by simpler means. In fact, some are merely absorbed into the host by a process like endocytosis. Others actually fuse their membranes. Remember those structures we were just talking about? They fuse their membranes with the host's membrane, allowing the entry of the viral genome into the cell.
Now, once inside the cell, the virus hijacks the machinery that the host cell uses in order to replicate itself. So remember, viruses are really small and they don't have all those necessary structures that are required to sustain life. So they have to use the structures that the host cell has in order to carry out those processes. So these host cells unwittingly, without their knowledge, provide nucleotides, enzymes, ribosomes, tRNA, amino acids, and even ATP to the virus so that the virus can replicate its genome and create new viruses and other viral products. Now, through this replicative process, the most important products to be produced are nucleic acids, right? The virus needs to replicate its viral genome and also capsomeres. The virus needs to build the components necessary to build a capsid to house the replicated viral genome so that it can create more viruses. Right? Its main goal, more or less, is to produce more of itself.
In this process, the virus actually doesn't have to go through the trouble of assembly. What's pretty amazing is in producing the viral genome and these capsomeres, these viruses actually spontaneously assemble. Now, spontaneous assembly is an idea we touched upon a long time ago when we were talking about membranes, cell membranes. And we said that cell membranes spontaneously assemble in an aqueous environment, meaning that those phospholipids arrange themselves into the proper orientation so that we produce the lipid bilayer. Now much like that, viruses also spontaneously assemble when the proper components are produced.