🧬 STRUCTURE OF A VIRUS

Let’s now understand what a virus is made of:

1. Size of Viruses

• Viruses are extremely small, much smaller than bacteria.
• Range: 20 nanometers (nm) (e.g., parvovirus) to 250 nm (e.g., poxvirus).
• They are 10 to 1000 times smaller than bacteria.
• Can pass through filters that even trap bacteria!

🔍 A nanometer is one-billionth of a meter. That’s super small.

2. Main Components of a Virus

Think of a virus like a chocolate:

• The filling inside is the genetic material (DNA or RNA).
• The chocolate coating is the protein coat (capsid).
• Some may have a wrapper (envelope) on the outside.

Let’s go through these:

🧬 a) Genome (Central Core)

• The genetic material of a virus is called its genome.
• This can be either:
  • DNA (like in T4 bacteriophage), or
  • RNA (like in HIV).
• It controls the virus’s ability to reproduce inside a host.

🛡️ b) Capsid (Protein Coat)

• This is a protective coat that surrounds the genome.
• Made of proteins.
• Built from smaller units called capsomeres.
• Capsid gives shape to the virus (like the shell of a turtle).

🧱 c) Nucleocapsid

• The combination of genome + capsid is called the nucleocapsid.

🧥 d) Envelope (Only in some animal viruses)

• Some viruses (like HIV) have an extra lipid layer around the capsid.
• This comes from the host’s cell membrane.
• Viruses with this layer are called enveloped viruses.
• Without it, they are called naked viruses.

💡 Mnemonic to Remember Components:
“Gives Cool New Energy”

• G = Genome
• C = Capsid
• N = Nucleocapsid
• E = Envelope

This will help you remember the 4 components in order!