Читать книгу Vaccines For Dummies - Sharon Perkins - Страница 20

A virus is put together like a burrito. The tortilla is the protein shell. The filling is the genetic instructions, or codes in the form of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid). The DNA strands are often but not always double strands; the RNA is usually but not always single stranded. This genetic code is what lets the virus reprogram and take over a cell.

Viruses can’t do anything on their own. That’s why they aren’t considered to be alive. They can’t make copies of themselves on their own. A virion all by itself isn’t enough to make you sick if it can’t get inside your cells. Viruses require what living things have in their cells to do what they do best — make copies of themselves. Once a virus is in a living cell, it’s almost like it is alive; it will turn that cell into a virus assembly machine.

Successful viruses turn our cells into photocopiers, churning out virions — more and more infectious viral particles. When we get sick, say with the flu, the cells in our bodies may produce as many as 100 trillion virions. That’s more than all the stars in the Milky Way.

With all of these copies, there are bound to be mistakes. Viruses make lots of mistakes. They often don’t copy their genetic material exactly the same each time. These miscopies are called mutations. Not all mutations are bad; many are dead ends. Headlines may say that a virus is mutating, but that’s just what viruses do. Viruses mutate; birds fly. Mutations, especially collecting over time, can lead to different variants or strains, and sometimes these changes can evade our immune responses or change how sick they make us.

There are many different types — or species — of viruses. Some viruses have round shells; some have long shells. Different viruses use different hooks, or receptors, to hold onto and enter a cell. A specific virus usually only infects a certain species or related species. If your dog gets a cold, you’re usually not going to get it. Sometimes, though, a virus can infect different species and can jump from ducks or pigs or bats to us. This jump across species often is another dead end, but sometimes it can lead to a virus that causes us a lot of problems.