In this lesson, we’ll review the definition of both cells and viruses. Then, we’ll compare and contrast the genetic material in cells to the different types of genetic material in viruses. Lastly, we’ll compare reproductive strategies for both.
Background on Cells and Viruses
Take a look at the table holding your computer.
Seems pretty solid, right? However, if you used a microscope, you would find a world full of moving parts not visible to the human eye. Tiny organisms are living on all the surfaces you can see. These living organisms are cells.Cells are the basic units of life, and in addition to the single celled bacteria growing on your table, cells also make up all the tissues and organs in our bodies. Without cells, you wouldn’t be able to study this lesson right now.Even smaller than cells are viruses. Unlike cells, viruses are non-living (arguably) infectious particles.
Although there are also differences in structure, size, and life cycle, today we’ll be comparing the genetic material and reproductive cycle of viruses versus cells.
Genetic Material in Cells ; Viruses
Genetic material is the instructions for all cell function. In cells, the genetic material is deoxyribonucleic acid (or DNA). DNA is made of individual pieces called nucleotides that are strung together in two long chains that twist together, forming a double helix.
The nucleotides hold a message inside DNA that is decoded by the cell to make proteins, molecules that are needed for all cell structure and function. In some cells, like our body cells, DNA is enclosed in a structure called the nucleus. Other cells, like bacteria, don’t have a nucleus and their DNA floats freely in the cytoplasm, or main compartment of the cell.
These organisms can reproduce faster than our cells can, with some dividing about every 20 minutes.To make proteins inside any type of cell, DNA is copied to another molecule called ribonucleic acid (or RNA) and then copied to proteins. This order is known as the central dogma and applies to all living cells. Consider it like baking a cake, first you have to cream the butter, then add the sugar, then add the flour. Your cake won’t turn out right if you don’t adhere to this order.
However, viruses break the rules a little bit. Viruses can use DNA or RNA as their genetic material. The DNA and RNA don’t even have to have the same structure as they do in normal cells. Cells have a double stranded DNA molecule and many strands of single stranded RNA as the copies.
Viruses, however, can have double stranded DNA, single stranded DNA, double stranded RNA, or single stranded RNA. They convert RNA to DNA and then back to RNA to make proteins, which does not happen inside cells.An example of a virus with a single stranded RNA genome is human immunodeficiency virus (HIV). This sexually or intravenously transmitted virus infects a type of immune cell called a T-cell, which protects the body against invaders. When HIV infects the T cells, it kills them, weakening the patient’s immune system and making them more susceptible to infection.
Reproduction in Cells and Viruses
Cell theory, which basically describes what cells are and do, was proposed by Robert Hooke in the 1800s. This scientist studied sections of cork, which comes from plants, under a microscope and found that it was made of little blocks, which he deemed cells. Building on his work he found that cells only come from other cells. Life cannot be created from non-life sources.
For example, flies don’t come from rotting meat, a prevailing idea before cell theory.Indeed, we now know that cells do, in fact, come from other cells. In bacteria, the cell replicates its DNA, grows larger, and splits in two in a process called binary fission. Human cells, with our nucleus and other structures have a more complex method of cell division. DNA is replicated, but the nucleus must dissolve and a complex network of proteins separates the DNA into two new cells in a process called mitosis.
Viruses need a living host, like a cell, to reproduce. It’s the inability to reproduce on their own that is the main argument for classifying them as not alive, though it’s still considered a gray area.
Viruses are like secret agents. They sneak into the body through an open cut, or lung and nasal passages, and latch onto an unsuspecting cell.The cell thinks the virus is a helpful particle and takes it in. However, once inside, the viruses hijacks the host cell’s machinery and forces it to make many copies of itself. New viruses are assembled by the host cell until they explode out, killing the host cell and releasing new virus particles to continue the infection.
The only goal of a virus is to reproduce, and in fact, some viruses reproduce too quickly, killing the host within days and spreading to new hosts, like the virus ebola. Other viruses, like HIV, live inside the host for decades, slowly killing off cells and making a home in their immune system.
Cells are the basic units of life. Cells can exist by themselves, like bacteria, or as part of a larger organism, like our cells.
Viruses are non-living infectious particles, much smaller than a cell, and need a living host to reproduce. The genetic material of the cell is DNA, a double stranded helix. Viruses however, can use DNA in a double or single strand, as well as RNA in a double or single strand.Single bacteria cells reproduce using binary fission (when the cell replicates its DNA, grows larger, and splits in two), while our cells use mitosis (which is when DNA is replicated, the nucleus dissolves, and a complex network of proteins separates the DNA into two new cells). Since viruses aren’t alive, they need to invade a host cell and hijack the host cell’s machinery to reproduce.