What is a virus, and how does it make you sick?Page 2 Answer sheet for this lesson (MS Word) (PDF version) Go to Page 1 DNA. You can think of DNA as a set of instructions for building proteins. Suppose I wanted you to build the tower of cubes in this photograph: Image 5 I might say something like: “Put the yellow block on top of the blue block. Then put the green block on top of the yellow block . . .” and so on. Every cell in your body contains DNA. It tells the cell how to combine different amino acids—the building blocks of proteins--into the proteins needed to build new cells. Why does every cell need these instructions? Go back to Google and ask “How long do human cells last?” Then ask the same question about some specific cells, such as human blood, skin or liver cells. 2) __________________________________ cells last for only ____________________________ (Write your answer on your answer sheet.) In order for you to live longer than whatever time you wrote in the space above, your body has to keep making new cells to replace the ones that keep dying. DNA tells the cells how to make the proteins it needs to make new, replacement cells. Enter the virus. A virus is basically a packet of instructions for building proteins surrounded by a fancy delivery system. When a virus enters your body, the delivery system goes to work, latching onto a cell and injecting new instructions into it that changes the way proteins are formed within the cell. Image 6 - (A virus injecting its protein-building instructions into a cell.) Imagine if someone took the instructions that I wrote to build the block tower (Image 5) and changed them to read “Put the red block on top of the blue block. Then put the yellow block on top of the red block . . .” The tower might end up looking like this: Image 7 When a virus changes the instructions for making proteins inside a cell, the cell starts making different proteins. And guess what: those proteins just happen to be the very proteins needed to make a copy of the virus. So instead of making replacement cells for your body, the cell starts making more viruses—often, thousands of them! Many of these viruses go on to invade other cells. Your immune system. Fortunately, your body will have none of this, and it goes into attack mode to try to get all those pesky viruses out of your body. This attack on the virus is launched by your body’s immune system. Your immune system surrounds the virus with antibodies . . . Image 8 - (Protective antibodies surrounding a virus.) . . . which creates all those nasty fluids in your lungs and sinuses that your body then tries to get rid of through coughing and sneezing. It can raise the temperature of the area around the virus, or even your whole body, to try to cook the virus to death. We call this a fever when this happens. In a way, all the horrible symptoms you experience when you have a cold or the flu aren’t really caused by viruses. They’re caused by you. Or rather, they’re caused by your body’s immune system as it attempts to rid your body of an invading virus before that virus has the chance to turn your entire body into one giant virus-making factory. Closing thoughts. Some viruses are very dangerous. Some viruses are now believed to cause cancer. But most viruses are harmless to people, and some may actually be helpful to us. Since viruses often change a cell’s DNA, one interesting question is: what, if any, role do viruses play in evolution? We really have no idea how many different viruses there are—or if some of them are helpful to us—because in general we study only harmful viruses. This gives us a very limited view of the role that viruses play in the overall progression of life on our planet. Although we know a lot about how some viruses can hurt us, there is still a lot to be learned about them. Addenda: 3/15 - A student has asked me if there are any videos about viruses. There are, but most of them are very technical and difficult to follow. The process by which a virus takes over a cell is very complicated. This one does a pretty good job of explaining how a virus works: What is a Virus? 4/8 - The original lesson stated that a virus was "a packet of DNA surrounded by a fancy delivery system." Not all viruses contain DNA. The SARS-CoV-2 virus, which causes COVID-19 disease, for example, contains RNA, not DNA. RNA is used by a cell to actually build the proteins according to the instructions contained in the DNA. So some viruses hyjack the protein-building process by changing the RNA rather than the DNA. I have changed to definition of a virus to "a packet of instructions for building proteins surrounded by a fancy delivery system," which is more accurate. BACK TO PAGE 1 BACK TO 5TH GRADE SCIENCE PAGE Last Updated: April 8,
2020
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