1. Viruses are the smallest type of biological particles. They cannot reproduce on their own. Here, we’ll show you one method by which viruses infect cells and use them to make copies of themselves, or replicate.

2. Viruses can have many different shapes. Here are just a few of them. Viruses can have many different shapes

3. Here is a simplified diagram of a bacterium, a single-celled organism that is much larger than a virus. Bacterium

4. The green circle represents the DNA of this bacterium. In bacteria, DNA is not contained within a nuclear membrane. This DNA is normally used to instruct this cell how to make proteins. Bacterial DNA

5. Here is a virus called a bacteriophage. It needs to attach to a specific type of bacterial cell in order replicate itself.

6. Like all viruses, this one has its reproductive molecule inside. It is called nucleic acid. nucleic acid DNA or RNA

7. Which can be either deoxyribonucleic acid, called DNA, or (click) ribonucleic acid, which is called RNA. You will learn more about these in later biology courses. nucleic acid DNA or RNA

8. The rest of the virus is made up of protein. The protein coat often has a geometrical shape, like this type of virus has. Protein Coat

9. After recognizing the bacterium as a suitable host, it attaches itself to it.

10. The nucleic acid now changes shape.

11. And is injected into the bacterium

12. Where it changes back into a near circular shape

13. This DNA or RNA from the virus takes control of the bacterial cell and uses the cell’s resources to make copies of itself.

14. These then direct the cell to manufacture proteins to use as building blocks for new viruses.

15. The proteins are now assembled into many brand new viruses, which are all exact copies of the original one that infected the cell.

16. Because there are so many copies formed, they cause the cell to swell and eventually, the (click) cell wall ruptures.

17. The newly produced viruses now leave the host cell and each one finds a new bacterial cell to infect.

18. And the whole cycle repeats itself.

19. click

26. click.

27. In this process, each bacterial cell that is used by a virus to replicate, is (click) destroyed by the virus. Later in biology, you will learn of another method viruses use to replicate, which does not immediately destroy the host cell.

28. Now, we’ll summarize the whole process in a table. The first step (click) is where the virus attaches itself to the bacterium. 1

29. Then the virus injects its reproductive material into the host bacterial cell 12

30. Then the reproductive material takes over the cell and uses its resources to make copies of itself 123

31. These use the resources of the cell to make proteins needed to build new copies of the virus 123 4

32. The proteins are assembled into many copies of the original virus. 123 4 5

33. The cell wall ruptures and the new viruses are released. 123 4 56

34. E ach released virus attaches to another cell and the process repeats itself. You can see that using this process, the population of viruses can grow very rapidly. Viruses can use a similar process to replicate and multiply in our body. 123 4 56

35. Luckily, we have an immune system which helps to bring their populations under control. You will learn more about the immune system as you go through this course. 123 4 56

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