Question

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

Short answer

(a) Complete viral particle. (b) Protein shell. (c) Viral genome + capsid. (d) Glycoproteins for host cell attachment.

Step-by-step solution

Define 'virion'

A virion is the complete, infective form of a virus outside a host cell. It consists of the viral genome surrounded by a protein coat and, in some cases, other layers.

Define 'capsid'

A capsid is the protein shell that encloses the viral genome. It protects the nucleic acid and aids in the transfer of the viral genome between host cells.

Define 'nucleocapsid'

A nucleocapsid is the combined entity of the viral nucleic acid and its capsid. It is the core component of the virus, necessary for its infectivity.

Define 'protein spike'

Protein spikes are glycoproteins projecting from the viral envelope or capsid. They play a crucial role in the virus's ability to infect host cells by binding to specific receptors on the host cell surface.

Key concepts

Virion

A virion is the complete form of a virus when it's outside a host cell. It's essentially the 'travelling' version of the virus. This means that it's equipped to infect other cells. Think of it like a little spaceship carrying everything it needs to start an infection. Virions contain several main components:

• The viral genome (which can be DNA or RNA).
• A protective protein shell called the capsid.

In some viruses, there might also be other layers like an envelope derived from the host cell membranes. This complete structure ensures that the virus can survive outside a host cell and successfully infect a new one.

Capsid

The capsid is the protein shell that surrounds and protects the viral genome. This shell is like a tough armor keeping the virus's genetic material safe from damage. The capsid is made up of protein molecules called capsomers. To imagine it better, think of the capsid as the outer wrapping paper on a gift.

Some important features of the capsid include:

• Protection of the genome from enzymes and other agents that might destroy it.
• Providing structural support to the virion.
• Helping the virus attach to and enter host cells.

The capsid's efficient design is crucial for the virus's ability to transfer its genetic material from one host cell to another.

Nucleocapsid

The nucleocapsid combines two crucial components: the viral nucleic acid (genome) and the capsid. When the genome and the capsid come together, they form the core structure necessary for viral infectivity. Imagine the nucleocapsid like an armored soldier protecting a vital message.

The nucleocapsid has several integral functions:

• Providing a strong protective layer for the genetic material.
• Ensuring the stability of the viral genome.
• Playing a role in the assembly of new virions once inside a host cell.

Overall, the nucleocapsid is central to the virus's ability to maintain its infective properties and successfully replicate within host cells.

Protein Spike

Protein spikes are glycoproteins that project from the viral envelope or the capsid. These spikes are essential tools the virus uses to recognize and attach to host cells. Think of protein spikes as keys that unlock the doors to host cells.

Some key points about protein spikes are:

• They help the virus attach to specific receptors on the surfaces of potential host cells.
• Enable the subsequent entry of the virus into the host cell.
• In some viruses, they play a role in fusion with the host cell membrane.

These spikes are indispensable for the infectivity of the virus, making them critical targets for antiviral drugs and vaccines.