What is a virus?
A virus is a tiny package of genetic instructions wrapped in a protein shell, far smaller than a bacterium. It can’t eat, grow or multiply on its own. To make copies, it has to get inside one of your cells and trick it into building new viruses.
A tiny package of instructions
A virus is mostly a strand of genetic code, DNA or RNA, packed in a shell of protein. It’s so small that a million could fit across the width of a hair, and it has no cell parts of its own to make energy or copies.
Share this stepSpikes fit your cells like a key
The spikes on its surface fit specific receptors on certain cells, like a key in a lock. That’s why a cold virus infects your nose and throat, while other viruses target the liver or the gut.
Share this stepIt turns the cell into a virus factory
Once inside, the virus releases its genetic code. The cell reads it as if it were its own instructions and starts building new viruses, often thousands, which burst out to infect the next cells.
Share this stepA virus is a hijacker, not a living cell.
Genetic codeyour cellnew viruses
That’s why antibiotics don’t work on viruses: they attack bacterial parts that viruses don’t have. Your immune system fights viruses, and vaccines train it in advance by showing it what the virus looks like.
Common follow-up questions
Is a virus alive?
Scientists disagree. A virus can’t do anything on its own outside a cell, but inside one it reproduces and evolves. Many describe it as being on the border of life.
What is the difference between a virus and bacteria?
Bacteria are living cells that can grow and multiply by themselves, and many are harmless or useful. Viruses are much smaller and can only multiply inside other cells.
How do viruses spread?
Depending on the virus: through droplets and air when someone coughs or talks, through touch and surfaces, through food and water, through blood or through insect bites.
Why do we keep getting colds?
Hundreds of different viruses cause colds, and some of them keep changing. Immunity to one doesn’t protect you from the others.
