Question

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

Short answer

A virion is a complete infectious virus. The capsid is its protein shell, the nucleocapsid is the viral genome plus capsid, and protein spikes are structures on the virion's surface.

Step-by-step solution

Define Virion

A virion is the complete, infectious form of a virus outside a host cell. It consists of the genetic material (DNA or RNA), a protein coat, and sometimes an outer lipid envelope.

Define Capsid

The capsid is the protein shell that encloses the genetic material of a virus. It is composed of protein subunits called capsomeres and helps protect the viral nucleic acid.

Define Nucleocapsid

The nucleocapsid refers to the combination of the viral genetic material and the capsid. Essentially, it is the complete set of genetic material enclosed within the protein shell.

Define Protein Spike

Protein spikes are protein structures that protrude from the surface of the virion. These spikes play essential roles in the virus's ability to attach to and enter host cells.

Key concepts

Virion

A virion is the complete and infectious form of a virus outside a host cell. Imagine it as the fully-assembled ship ready to sail and invade a new territory. It consists of:

• **Genetic material**: This can be either DNA or RNA, carrying the instructions for making new virus particles.


• **Protein coat**: Also known as the capsid, this protective layer surrounds the genetic material.


• **Lipid envelope**: Some viruses also have an outer lipid layer, which they acquire from the host cell membrane upon exiting the host cell.

The virion ensures that the viral genetic material is protected and can efficiently enter a new host cell for replication.

Capsid

The capsid is the protein shell that encases the viral genetic material. Think of it as the armor of the virus, made up of protein subunits called capsomeres.

The capsid has several crucial functions:

• **Protection**: It shields the fragile genetic material from physical damage and enzymatic degradation.


• **Attachment**: In some viruses, the capsid can bind to host cells to initiate infection.


• **Shape and Size**: It provides the structural integrity and determines the shape and size of the virus.

Understanding the capsid's role helps us appreciate how viruses can be so resilient and versatile in various environments.

Nucleocapsid

The nucleocapsid is a combination of the viral genetic material and the capsid. Picture it as the fortified vault that securely holds the virus's blueprint.

Here’s what it entails:

• **Genetic Material**: This could be DNA or RNA, depending on the type of virus.


• **Capsid**: This outer protein shell encloses and protects the genetic material.

In essence, the nucleocapsid is like the core unit that is essential for the virus's capability to infect and replicate within a host cell.

It ensures that the genetic material is both protected and able to be delivered into the host cell efficiently.

Protein Spike

Protein spikes are like the keys that allow the virus to unlock and enter host cells. These structures protrude from the virion’s surface and play crucial roles:

• **Attachment**: They bind to specific receptors on the surface of the host cell, initiating the infection process.


• **Entry**: Depending on the virus, protein spikes can facilitate the fusion of the viral envelope with the host cell membrane or trigger endocytosis.

Understanding protein spikes is vital because they are often the target for vaccines and antiviral drugs, which aim to block their ability to bind and enter host cells.