Viruses: Living or Non Living?
Viruses are considered to be lifeless because they don't have all 8 characteristics of life. The 8 characteristics of life are:
1. All life is made up of at least one cell
2. All life has to eat
3. All life grows/increases its biomass
4. All life reproduces itself
5. All life responds to it's environment
6. All life adapts/evolves
7. All life maintains internal and external homeostasis
8. All life ends
A virus can't reproduce itself on it's own, it needs to take over a host cell and force it to help with reproduction. Viruses don't contain any cytoplasm but don't have any specific cell organelles such as ER or Golgi body. They also don't have a nucleus, just DNA or RNA in a capsid. Viruses don't grow or develop, use energy or respond to their environment which are all required by living things. Wendell Stanley discovered viruses through an experiment with tobacco leaves and found out that viruses can be crystallized, have water added back and return to their previous state. All life dies without water, so therefor a virus is non-living.
1. All life is made up of at least one cell
2. All life has to eat
3. All life grows/increases its biomass
4. All life reproduces itself
5. All life responds to it's environment
6. All life adapts/evolves
7. All life maintains internal and external homeostasis
8. All life ends
A virus can't reproduce itself on it's own, it needs to take over a host cell and force it to help with reproduction. Viruses don't contain any cytoplasm but don't have any specific cell organelles such as ER or Golgi body. They also don't have a nucleus, just DNA or RNA in a capsid. Viruses don't grow or develop, use energy or respond to their environment which are all required by living things. Wendell Stanley discovered viruses through an experiment with tobacco leaves and found out that viruses can be crystallized, have water added back and return to their previous state. All life dies without water, so therefor a virus is non-living.
Lytic and Lysogenic Cycles
You unfortunately get a cold sore on your lip... again. Ever wonder why it comes and goes? Well, when you first got the cold sore virus, a bacteriophage injects its viral DNA into a host cell and the viral DNA forms a circle. From there the cell will go into the lytic cycle; the viral DNA takes over the hosts metabolism causing synthesis of new bacteriophage proteins and nucleic acid. These are exact copies of the virus that infected the host cell. Finally, the cell lyses or bursts, ejecting lots of viruses that will now go and infect other cells. This is when you'd see the cold sore appear on your lip, when lots of cells are being infected in that area by the virus. Once the cold sore has run its course, the virus will go into the lysogenic cycle, which is the point where you don't see a cold sore anymore. The virus is still in your body system just not visible. During the lysogenic cycle, once the viral DNA has been injected into the host cell, it'll join the circle of the host cells DNA. This way, when the cell divides or reproduces, the prophage will also be copied into the new cell. The prophage and host DNA will then separate into circles again and either go through the lysogenic cycle again, or go into the lytic cycle, unfortunately leaving you with another cold sore.
How Does Our Body Defend Against Pathogens?
Phagocytosis: is the process where extensions of cytoplasm on a white blood cell eat or engulf large particles and take them into the cell. Part of your bodies second line of defence, it makes millions of white blood cells to destroy the pathogen, which they do with enzymes in their lysosomes. For example, if bacteria enter through a wound, the blood vessels in the area expand, allowing the phagocytes to move into the area and engulf the bacteria and cell debris.
Immune system: has specific defences that attack a pathogen triggered by an antigen. Our immune system is what keeps us healthy! Without it, we'd have no defence agains bacteria and viruses.
-Interferon: one of a group of proteins that help cells resist viral infection. It's made by an infected host cell before it dies, signals other cells to defend against the virus and can activate any immune cells to kill the virus too. They're called interferons because they "interfere" with how fast the virus grows. They slow the growth, giving the specific defences of the immune system time to respond.
-Antibodies: are a very specific protein made by white blood cells that help destroy pathogens. They attach to a virus, deactivate them by clumping them together which makes it easier for other white blood cells to destroy the virus. Antibodies travel through the blood stream to attack the pathogen. They stop when they overcome the infection and the plasma cells die out and stop making more antibodies. Memory B cells remember the virus, so if it attacks again, they can likely stop it before you even know it's there.
Vaccines: injection of weakened or mild form of pathogens that create immunity to that pathogen. Your body makes antibodies towards the pathogen injected, so your body is more or less immune to the virus.
Immune system: has specific defences that attack a pathogen triggered by an antigen. Our immune system is what keeps us healthy! Without it, we'd have no defence agains bacteria and viruses.
-Interferon: one of a group of proteins that help cells resist viral infection. It's made by an infected host cell before it dies, signals other cells to defend against the virus and can activate any immune cells to kill the virus too. They're called interferons because they "interfere" with how fast the virus grows. They slow the growth, giving the specific defences of the immune system time to respond.
-Antibodies: are a very specific protein made by white blood cells that help destroy pathogens. They attach to a virus, deactivate them by clumping them together which makes it easier for other white blood cells to destroy the virus. Antibodies travel through the blood stream to attack the pathogen. They stop when they overcome the infection and the plasma cells die out and stop making more antibodies. Memory B cells remember the virus, so if it attacks again, they can likely stop it before you even know it's there.
Vaccines: injection of weakened or mild form of pathogens that create immunity to that pathogen. Your body makes antibodies towards the pathogen injected, so your body is more or less immune to the virus.
Binary Fission and Conjugation
Binary Fission: After cell copies it's genetic material it splits in half, creating two identical daughter cells. It involves one parent (asexual reproduction). This is an advantage because one organism can ensure the entire species survival. Another advantage to Binary Fission is that the reproduction rate is much quicker, and a larger amount of offspring are produced. All offspring are genetically identical though and this is a disadvantage because one virus could wipe out all the bacteria.
Conjugation: Direct transfer of genes between bacteria. Requires 2 parents (sexual reproduction) and produces genetically diverse offspring. Compared to Binary Fission this an advantage because one virus couldn't wipe out the whole population because of the genetic diversity. Some disadvantages however would be that a mate is needed and that it takes a longer time to make cells than it does with Binary Fission. Cells sexually reproduce with F-factor. F-factor is the ability for a cell to form a conjugation tube. This is coded in a sequence of DNA and is either part of a plasmid or bacterial chromosome. Only some cells have F-factor, so it can be hard to find a mate. F-factor can be given to the other cell though during conjugation if it's coded in the plasmid. Overall the only similarities between Binary Fission and Conjugation is that they're both types of reproduction and they involve DNA and in some cases plasmids. |
Bacteria Altering its Genetic Information
Transduction: when foreign DNA is introduced from a virus to bacteria. It's introduced by a bacteriophage when it injects its nucleic acid into the host cell. An enzyme is produced that breaks down the host cell's DNA, and phage coded proteins are made. When the mature phages are forming, a phage head could surround bacterial DNA rather than phage DNA. When this particle is ejected from the cell it will go on to inject another cell with the bacterial DNA. This DNA will become integrated with the new cells bacterial chromosome, so every time this cell reproduces it will pass on the new genetic information.
Transformation: is when genes are taken up from the environment. Some different types of bacteria have proteins on their surface that can transport DNA from closely related cells. This DNA is from a cell that has died and broke open, releasing the DNA inside. When inside a closely related cell, it integrates itself with the DNA already there so when the cell reproduces it will then pass on the genetic information.
Transformation: is when genes are taken up from the environment. Some different types of bacteria have proteins on their surface that can transport DNA from closely related cells. This DNA is from a cell that has died and broke open, releasing the DNA inside. When inside a closely related cell, it integrates itself with the DNA already there so when the cell reproduces it will then pass on the genetic information.
Evolution of Antibiotic Resistance
The first antibiotic produced was penicillin. People thought that this was the new cure to everything, that scientists could eradicate any bacteria that's a health threat... little did they know of superbugs! Penicillin was given to it's first patient in 1941 but by 1942 there was resistance reported. Resistance is made possible by taking antibiotics when it isn't needed or not finishing the amount prescribed. If you have an infection and take antibiotics for the first couple days but stop because you feel fine, it doesn't mean that all the bad bacteria has been killed. In fact, you could've just helped make a superbug. In the first few days of taking antibiotics it'll kill all the least resistant bacteria but not the most resistant. So by natural selection soon all the bacteria will be bad and resistant! Since microbes are always randomly mutating, a mutation could occur that makes it more resistant to antibiotics therefor not getting killed off right away. Vancomycin is an antibiotic that was introduced in 1956. By 2002 all bacteria is resistant to this drug, and is no longer effective! Potentially, one day all antibiotics that we use now could be ineffective. That's a scary thought. Something else that's scary is that cells can share this immunity to bacteria. For example, Staph Aureus gained a Vancomycin resistant gene from Entercocci bacteria. Antibacterial resistance can be spread to other bacteria within an infected person or to bacteria in another organism by conjugation, transformation and transduction which I explained earlier. There are over 10 antibiotics with resistance, so make sure you finish all of your prescribed pills and not demand them when it isn't necessary!