Although viruses have a genome, they need to take over the machinery of other living cells to follow the virus genome instructions. So, viruses cannot reproduce by themselves. Next, all living things have metabolism.
Metabolism means the ability to collect and use energy. Chemical reactions in your cells constantly change molecules into forms of energy we can use.
The energy you use to run and jump came from breaking big food molecules into smaller pieces that can be used or stored in the cell. Viruses are too small and simple to collect or use their own energy — they just steal it from the cells they infect. Viruses only need energy when they make copies of themselves, and they don't need any energy at all when they are outside of a cell.
Finally, living things maintain homeostasis , meaning keeping conditions inside the body stable. Your body sweats to cool you down and shivers to warm you up if its temperature changes from Millions of adjustments throughout the day keep your temperature and the chemicals in your body balanced.
Viruses have no way to control their internal environment and they do not maintain their own homeostasis. So, since viruses cannot reproduce on their own and have no metabolism or homeostasis, they are usually not thought of as truly alive.
They do have a huge effect on living things during infections, though! What do you think? Should viruses be included with other living things? After you decide why you think they should or should not be considered alive, listen to biochemist Nick Lane and Dr.
Biology discuss if they think viruses are alive. By volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteers page to get the process started. Digging Deeper. Digging Deeper: Depression and the Past. Digging Deeper: Germs and Disease. Digging Deeper: Milk and Immunity. Capsid: a protective shell around the genome of a virus.
Homeostasis: the ability to keep a system at a constant condition. View Citation You may need to edit author's name to meet the style formats, which are in most cases "Last name, First name.
Bibliographic details: Article: Viruses Author s : Dr. Modern Language Association, 7th Ed. Download comic as a PDF packet.
Some are additionally enveloped in a soft, lipid wrapping. These tiny virus packages are just tens to a few hundreds of nanometers across. This makes them smaller than most bacteria, which can be a small as roughly a tenth the size of a human blood cell.
Such a tiny size means that you can't even spot most viruses with a light microscope. The one exception, a group known as giant viruses , has members with astonishingly large genomes. These mega-viruses are hundreds of times larger than most, with capsids that span roughly to nanometers across and full viral forms that can measure up to nanometers across. Due to their simple structure, viruses cannot move or even reproduce without the help of an unwitting host cell.
But when it finds a host, a virus can multiply and spread rapidly. To identify the correct host, viruses have evolved receptors on their surfaces that match up with those of their ideal target cell, letting the virus get its genetic material inside and hijack its host's cellular machinery to help it reproduce by multiplying the virus' genetic material and proteins. Using that strategy, the minute marauders have flourished and evolved in step with their hosts. By one estimate , at least , different viruses can infect mammals alone, and even this massive number may be on the low side.
This viral army can cause symptoms as mild as a cough or as deadly as internal bleeding. Some viruses may even cause the runaway cellular growth that is the root of cancer, as is thought to be the case with human papillomavirus and cervical cancer.
Inside their cellular hosts, viruses can create an enormous number of copies and spread the infection to other cells. For example, if you get the flu, your body will be riddled with some hundred trillion viruses in just a few days —more than 10, times the number of people on Earth. How viruses spread from person to person depends on the type.
Many hitch a ride in the mist of droplets that flies from your mouth every time you cough or sneeze. A variety of factors can influence how fast these airborne viruses can spread. Flu, for one, seems to survive longer in cool, dry environments , which may be the source of its common winter spread. But in tropical regions, high humidity seems to help the flu jump from person to person.
Other viruses spread most easily through contact with other bodily fluids. For example, Ebola virus spreads from contact with infected blood, feces, or vomit. Unlike many other viruses, scientists think Ebola cannot spread through the air after people with the virus cough or sneeze. Still other viruses travel through an intermediary, like a mosquito, which then infects people by biting them. One example of these so-called mosquito-born diseases is dengue, which causes a potentially deadly flu-like infection.
The risk of dengue has risen in recent years, currently threatening roughly half of the global population, according to the World Health Organization. Other notorious mosquito-born diseases include Zika, Chikungunya, and West Nile. By Michael Le Page. An illustration of a mimivirus, which consists of outer hairs and DNA enclosed in protein.
The finding will fuel an already fierce debate about whether giant viruses really are viruses, and if they are alive or not. Why any virus needs to produce its own energy remains a mystery, he says.
0コメント