Question

Define the following: (a) virion (b) capsid (c) nucleocapsid (d) protein spike

Short answer

A virion is a complete virus outside a cell. A capsid is its protective protein coat. A nucleocapsid combines genetic material and capsid. Protein spikes aid in host cell entry.

Step-by-step solution

- Define virion

A virion is the complete, infectious form of a virus outside a host cell, with its genetic material encased in a protein coat.

- Define capsid

A capsid is the protein shell that encases the genetic material of a virus, protecting it and aiding in its delivery to host cells.

- Define nucleocapsid

A nucleocapsid refers to the combination of the viral genetic material and the capsid protein that encapsulates it.

- Define protein spike

Protein spikes are glycoproteins protruding from the lipid envelope or capsid of a virus, facilitating attachment and entry into host cells.

Key concepts

virion

A virion is the complete and infectious form of a virus when it's outside a host cell. Think of it as the 'ready to infect' state of the virus. In this state, it's often inert and can't replicate on its own. It must first infect a host cell to start the replication process. Virions are equipped with genetic material surrounded by a protective protein coat, which helps them withstand the extracellular environment and remain infectious.

capsid

The capsid is the protein shell of a virus that encases and protects its genetic material. Imagine it like a protective armor for the virus's core. The capsid is made up of protein subunits called capsomeres. These subunits assemble into a structure that ensures the virus's genetic material is safeguarded until it finds a suitable host. Additionally, the capsid plays a key role in delivering the viral genetic material into the host cell, often by interacting with cell membranes.

nucleocapsid

The nucleocapsid is a distinct component in some viruses, where the genetic material of the virus is enclosed within the capsid protein structure. It essentially refers to the combination of the viral DNA or RNA and the capsid that surrounds it. This structure ensures that the genetic material is both protected and properly packaged to be efficiently transmitted into a new host cell. In some viruses, nucleocapsids are further enclosed in an additional lipid envelope, which is derived from the host cell's membrane.

protein spike

Protein spikes are glycoproteins that protrude from the surface of a virus, either from the lipid envelope or directly from the capsid. These spikes are crucial for the virus's ability to infect host cells. They act like keys, allowing the virus to attach to and enter specific cells by binding to receptor molecules on the cell surface. Without these protein spikes, viruses would struggle to find their way into the host cells to begin the infection process. Spikes are often targets for antibodies, which makes them important for vaccine development.