IB Biology Topic A2.3 Viruses Revision Notes (HL)

Virus Structure: What Makes Viruses Different from Cells

Definition

Virus

A virus is a non-cellular particle composed of genetic material (DNA or RNA) enclosed in a protein coat called a capsid.

A virus is a non-cellular particle composed of genetic material (DNA or RNA) enclosed in a protein coat (capsid).
Viruses lack the structures and processes for independent life and can only reproduce by infecting a host cell.
They are obligate intracellular parasites, depending entirely on host cells to replicate.

Small and Fixed Size:
Viruses range from 20 to 300 nanometers, much smaller than bacteria and cells.
Their small size allows them to invade host cells and evade immune defenses.
Viruses do not grow after assembly, and their size is set by capsid protein arrangement.

Hint

Viruses are assembled inside host cells, much like a car is built in a factory.
They do not grow or develop like living organisms.

Definition

Virus

A virus is a non-cellular particle composed of genetic material (DNA or RNA) enclosed in a protein coat called a capsid.

A virus is a non-cellular particle composed of genetic material (DNA or RNA) enclosed in a protein coat (capsid).
Viruses lack the structures and processes for independent life and can only reproduce by infecting a host cell.
They are obligate intracellular parasites, depending entirely on host cells to replicate.

Small and Fixed Size:
Viruses range from 20 to 300 nanometers, much smaller than bacteria and cells.
Their small size allows them to invade host cells and evade immune defenses.
Viruses do not grow after assembly, and their size is set by capsid protein arrangement.

Hint

Viruses are assembled inside host cells, much like a car is built in a factory.
They do not grow or develop like living organisms.