The capsid is a protein shell that encases and protects the viral genetic material (either DNA or RNA). Its primary roles in viral reproduction include:
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Protection: The capsid protects the viral genetic material from degradation by enzymes and other environmental factors.
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Attachment: The capsid plays a crucial role in the initial stage of viral infection by facilitating the attachment of the virus to the host cell membrane. Specific proteins on the capsid can bind to receptors on the host cell, enabling the virus to enter the cell.
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Delivery of Genetic Material: Once attached, the capsid often facilitates the delivery of the viral genetic material into the host cell. In some cases, the capsid may disassemble or release the genetic material after entry.
During the viral replication cycle, the host cell's machinery is hijacked to replicate the viral genome and produce new capsid proteins, which then assemble around the newly replicated viral genomes to form new virus particles.
Regarding your options, it seems they were slightly misphrased. Here’s a clarification:
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"One the capsid copies the viral DNA to the capsid copies the host cell DNA." This statement is incorrect; the capsid itself does not copy DNA.
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"Three, the capsule attaches to the cell membrane." This is partially correct; the capsid (not a capsule) does attach to the cell membrane to facilitate entry into the host cell.
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"For the capsid ends the lytic cycle." This statement is misleading; the capsid doesn't end the lytic cycle but is involved in the assembly and release of new virions.
In summary, the capsid's primary role is in protecting the viral genome and facilitating the virus's entry into host cells, which is crucial for viral reproduction.