Viruses
(By Gramajo)
Are viruses alive?
Are viruses alive?
No, they are not.
No, they are not.
Why though?
Why though?
They do not exhibit all of the characteristics of life. For instance, they are unable to take in nutrients or use energy, reproduce on their own without a host cell (via receptors on the plasma membrane of the host), or even maintain homeostasis; they don't move nor even make their own proteins, they're just there existing! Basically, a virus is a nonliving strand of genetic material within a protein coat.
They do not exhibit all of the characteristics of life. For instance, they are unable to take in nutrients or use energy, reproduce on their own without a host cell (via receptors on the plasma membrane of the host), or even maintain homeostasis; they don't move nor even make their own proteins, they're just there existing! Basically, a virus is a nonliving strand of genetic material within a protein coat.
Difference between cells and viruses:
Difference between cells and viruses:
Living things have cells, viruses have a protein coat.
Living things have cells, viruses have a protein coat.
Living things make a copy of themselves, viruses insert their genetic material into a host cell.
Living things make a copy of themselves, viruses insert their genetic material into a host cell.
Living things use energy, viruses use a mechanism when in contact with a host cell.
Living things use energy, viruses use a mechanism when in contact with a host cell.
Living things respond to stimulus, viruses interact with the cells they infect, but most of this is simply based on virus anatomy.
Living things respond to stimulus, viruses interact with the cells they infect, but most of this is simply based on virus anatomy.
How are viruses classified?
How are viruses classified?
They are generally classified by the type of nucleic acid they contain.
They are generally classified by the type of nucleic acid they contain.
However, that can also depend on their morphology, DNA or RNA, mode of replication, the organisms they infect and the type of disease they cause. Viruses can also be classified by the design of their capsids.
However, that can also depend on their morphology, DNA or RNA, mode of replication, the organisms they infect and the type of disease they cause. Viruses can also be classified by the design of their capsids.
Example from McGraw Hill:
Example from McGraw Hill:
As you can see, most of these viruses contain capsids and their genetic material (which can vary between RNA and DNA depending the virus, also used for classification), however, they may have different structures such as a tail and tail fiber such as the bacteriophage or an envelope like the influenza virus (which is related to the COVID-19).
As you can see, most of these viruses contain capsids and their genetic material (which can vary between RNA and DNA depending the virus, also used for classification), however, they may have different structures such as a tail and tail fiber such as the bacteriophage or an envelope like the influenza virus (which is related to the COVID-19).
How do viral infections occur?
How do viral infections occur?
By entering a host cell, basically.
By entering a host cell, basically.
In more elaborate terms:
In more elaborate terms:
As it was stated, a virus enters a host cell and attaches itself using receptors on the plasma membrane of the host (depending on the cell, it may be compatible or not), once it is successfully attached, the genetic material of the virus enters the cytoplasm of the host, exposing the genetic material that instructs the cell to make more of the virus, finally ending with a programmed death of the cell, thus, bursting many more viruses that will infect more cells.
As it was stated, a virus enters a host cell and attaches itself using receptors on the plasma membrane of the host (depending on the cell, it may be compatible or not), once it is successfully attached, the genetic material of the virus enters the cytoplasm of the host, exposing the genetic material that instructs the cell to make more of the virus, finally ending with a programmed death of the cell, thus, bursting many more viruses that will infect more cells.
What is the difference between the lytic and lysogenic cycle?
What is the difference between the lytic and lysogenic cycle?
Lytic Cycle
Lytic Cycle
In the lytic cycle, the host cell makes many copies of the viral RNA or DNA and instructs the host cell to make more viral protein capsids and enzymes needed for viral replication. The protein coat forms around the nucleic acid of new viruses. These new viruses leave the cell by causing the cell to burst, releasing the viruses to infect other cells.
In the lytic cycle, the host cell makes many copies of the viral RNA or DNA and instructs the host cell to make more viral protein capsids and enzymes needed for viral replication. The protein coat forms around the nucleic acid of new viruses. These new viruses leave the cell by causing the cell to burst, releasing the viruses to infect other cells.
Lysogenic cycle
Lysogenic cycle
The viral DNA enters and integrates itself into the nucleus' chromosomes of the host cell once the genetic material of the virus enters the cytoplasm. Once integrated, the host cell has the viral genes permanently. The genes remain dormant and are activated depending on given varying circumstances, thus, resulting in the lytic cycle.
The viral DNA enters and integrates itself into the nucleus' chromosomes of the host cell once the genetic material of the virus enters the cytoplasm. Once integrated, the host cell has the viral genes permanently. The genes remain dormant and are activated depending on given varying circumstances, thus, resulting in the lytic cycle.
What is a retrovirus? What is the evolutionary advantage for viruses that have RNA as genetic material?
What is a retrovirus? What is the evolutionary advantage for viruses that have RNA as genetic material?
A.) Basically, a retrovirus is a type of virus that has RNA as its genetic material instead of DNA (a virus may either have DNA or RNA, but never both). They are also known for having a complex replication cycle. Retroviruses are a type of virus that use a special enzyme called reverse transcriptase to translate its genetic information into DNA. That DNA can then integrate into the host cell's DNA.
A.) Basically, a retrovirus is a type of virus that has RNA as its genetic material instead of DNA (a virus may either have DNA or RNA, but never both). They are also known for having a complex replication cycle. Retroviruses are a type of virus that use a special enzyme called reverse transcriptase to translate its genetic information into DNA. That DNA can then integrate into the host cell's DNA.
B.) In general, RNA viruses tend to have high mutation rates, while DNA viruses tend to have low mutation rates. This is because most DNA viruses copy their genetic material using enzymes from the host cell which catch and fix mistakes as they go. RNA, on the other hand, use enzymes which don't proofread and make many more mistakes, but at a higher speed, another advantage includes the fact that the RNA permanently integrated into the host genome, having long lasting effects on the cell.
B.) In general, RNA viruses tend to have high mutation rates, while DNA viruses tend to have low mutation rates. This is because most DNA viruses copy their genetic material using enzymes from the host cell which catch and fix mistakes as they go. RNA, on the other hand, use enzymes which don't proofread and make many more mistakes, but at a higher speed, another advantage includes the fact that the RNA permanently integrated into the host genome, having long lasting effects on the cell.