Final answer:
A virus's capsid facilitates its entry into a host cell. Bacteriophages infect bacteria using lytic and lysogenic cycles. The specificity of viral infection depends on the presence of specific receptors on host cells for virus attachment.
Step-by-step explanation:
A virus's protein coat, also known as a capsid, helps it to enter a host cell by tricking the host cell into taking the virus inside. Bacteriophages are types of viruses that specifically infect bacteria, employing two primary types of cycles. In the lytic cycle, phages effectively hijack the bacterial machinery, producing new phages and releasing viral enzymes that cause lysis - the rupturing of the bacterium's cell wall - to release newly formed virions.
Conversely, the lysogenic cycle allows phages to integrate into the bacterial genome and remain inactive, replicating along with the host cell through several cell divisions before potentially entering the lytic cycle.
Bacteriophages attach to bacterial cells by binding to specific receptor molecules on the cell's surface. Once attached, they inject their genetic material into the host cell, leaving the capsid outside. The host's molecular machinery is then co-opted to replicate the phage's DNA and produce the proteins necessary for producing new phages. Eventually, after about twenty minutes, new phages can assemble within the host cell and then be released, often by lysis of the host cell.
The specificity of viral infections is remarkable, with most viruses having a limited host range; they can only infect specific hosts and certain cell types within those hosts. This specificity is largely due to the presence of specific viral receptors on the host cell surface required for the virus to attach. After entry into the host cell, a virus will replicate its genome and produce proteins necessary for the formation of new virus particles, which can cause cell damage or even cell death.