Review:
An album with a set of good photos of the major viruses, supported by an excellent introduction of the subject.
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1. Archaea – single celled organisms, whose cells have no nucleus and able to withstand extreme temperatures and highly acidic conditions. Their membranes are hydrocarbon chains
2. Bacteria - single celled organisms, whose cells have no nucleus. Their membranes are made of fatty acid chains.
3. Eukarya members have a nucleus containing genetic material and are represented by four kingdoms: Plantae, Protista, Animalia, and Fungi.
There are proposals to add two more that represent non-cellular life:
4. Nucleocytoplasmic Large DNA viruses (also called Megavirales)
5. Prionobiota (acellular and without nucleic acid) and Virusobiota (acellular but with nucleic acid)
A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.
While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles. These viral particles, also known as virions, consist of two or three parts:
· the genetic material made from either DNA or RNA, long molecules that carry genetic information;
· a protein coat, called the capsid, which surrounds and protects the genetic material; and in some cases
· an envelope of lipids that surrounds the protein coat when they are outside a cell.
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Notes:
Tree of life consists of three domains:1. Archaea – single celled organisms, whose cells have no nucleus and able to withstand extreme temperatures and highly acidic conditions. Their membranes are hydrocarbon chains
2. Bacteria - single celled organisms, whose cells have no nucleus. Their membranes are made of fatty acid chains.
3. Eukarya members have a nucleus containing genetic material and are represented by four kingdoms: Plantae, Protista, Animalia, and Fungi.
There are proposals to add two more that represent non-cellular life:
4. Nucleocytoplasmic Large DNA viruses (also called Megavirales)
5. Prionobiota (acellular and without nucleic acid) and Virusobiota (acellular but with nucleic acid)
A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.
While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles. These viral particles, also known as virions, consist of two or three parts:
· the genetic material made from either DNA or RNA, long molecules that carry genetic information;
· a protein coat, called the capsid, which surrounds and protects the genetic material; and in some cases
· an envelope of lipids that surrounds the protein coat when they are outside a cell.
The average virion is about one one-hundredth the size of the average bacterium.
The difference between DNA and RNA in the most basic way is that DNA is double stranded whereas RNA is single stranded. The next difference is that DNA is made from deoxyribose and RNA is made from ribose. DNA is contained within the nucleus of a cell and cannot leave. The job of RNA is to copy a strand of DNA in the nucleus to carry out the manufacture of a specific protein, carry the code outside into the cytoplasm of the cell, where it attaches to a ribosome that manufactures protein strands to become amino acids. Each strand of RNA can carry the recipe for several protein strands.
In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein. However, retroviruses function differently, as their RNA is reverse-transcribed into DNA, which is integrated into the host cell's genome (when it becomes a provirus), and then undergoes the usual transcription and translational processes to express the genes carried by the virus.
There are seven classes of viruses:
1. dsDNA viruses – with double-stranded DNA genomes. They land on a bacterial cell and inject their DNA into the cell. The virus DNA destructs host’s DNA and use it as a building blocks for its replication. The virus gets multiplied and when cell is full, it ruptures and viruses can go and start the cycle again.
2. ssDNA viruses – with single-stranded DNA genomes. The virus enters the plant by feeding insect. Two its DNA segments move into nucleus and convert into double-stranded DNA. Replicated viruses move to neighbouring cells and are acquired by the other insects to propagate firther.
3. dsRNA viruses – double-stranded RNA viruses. Include a group called rotaviruses. Rotavirus is the most common cause of diarrhoeal disease among infants and young children.
4. (+)ssRNA viruses - A positive-sense single-stranded RNA virus uses positive sense, single-stranded RNA as its genetic material. Single stranded RNA viruses are classified as positive or negative depending on the sense or polarity of the RNA. They account for a large fraction of known viruses, including many pathogens such as the hepatitis C virus, West Nile virus, dengue virus, and SARS and MERS coronaviruses, as well as less clinically serious pathogens such as the rhinoviruses that cause the common cold.
5. (−)ssRNA viruses - A negative-sense single-stranded RNA virus uses negative sense, single-stranded RNA as its genetic material. The negative viral RNA must be converted to a positive RNA. Therefore, is not infectious by itself.
6. ssRNA-RT viruses - A retrovirus is a single-stranded positive-sense RNA virus with a DNA intermediate and, as an obligate parasite, targets a host cell.
In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein. However, retroviruses function differently, as their RNA is reverse-transcribed into DNA, which is integrated into the host cell's genome (when it becomes a provirus), and then undergoes the usual transcription and translational processes to express the genes carried by the virus.
7. dsDNA-RT viruses – double-stranded retroviruses are also called "pararetrovirus.
There is about 10 million viruses in each millilitre of seawater. They infect bacteria, which burst apart and their remains are consumed by other life forms.
The difference between DNA and RNA in the most basic way is that DNA is double stranded whereas RNA is single stranded. The next difference is that DNA is made from deoxyribose and RNA is made from ribose. DNA is contained within the nucleus of a cell and cannot leave. The job of RNA is to copy a strand of DNA in the nucleus to carry out the manufacture of a specific protein, carry the code outside into the cytoplasm of the cell, where it attaches to a ribosome that manufactures protein strands to become amino acids. Each strand of RNA can carry the recipe for several protein strands.
In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein. However, retroviruses function differently, as their RNA is reverse-transcribed into DNA, which is integrated into the host cell's genome (when it becomes a provirus), and then undergoes the usual transcription and translational processes to express the genes carried by the virus.
There are seven classes of viruses:
1. dsDNA viruses – with double-stranded DNA genomes. They land on a bacterial cell and inject their DNA into the cell. The virus DNA destructs host’s DNA and use it as a building blocks for its replication. The virus gets multiplied and when cell is full, it ruptures and viruses can go and start the cycle again.
2. ssDNA viruses – with single-stranded DNA genomes. The virus enters the plant by feeding insect. Two its DNA segments move into nucleus and convert into double-stranded DNA. Replicated viruses move to neighbouring cells and are acquired by the other insects to propagate firther.
3. dsRNA viruses – double-stranded RNA viruses. Include a group called rotaviruses. Rotavirus is the most common cause of diarrhoeal disease among infants and young children.
4. (+)ssRNA viruses - A positive-sense single-stranded RNA virus uses positive sense, single-stranded RNA as its genetic material. Single stranded RNA viruses are classified as positive or negative depending on the sense or polarity of the RNA. They account for a large fraction of known viruses, including many pathogens such as the hepatitis C virus, West Nile virus, dengue virus, and SARS and MERS coronaviruses, as well as less clinically serious pathogens such as the rhinoviruses that cause the common cold.
5. (−)ssRNA viruses - A negative-sense single-stranded RNA virus uses negative sense, single-stranded RNA as its genetic material. The negative viral RNA must be converted to a positive RNA. Therefore, is not infectious by itself.
6. ssRNA-RT viruses - A retrovirus is a single-stranded positive-sense RNA virus with a DNA intermediate and, as an obligate parasite, targets a host cell.
In most viruses, DNA is transcribed into RNA, and then RNA is translated into protein. However, retroviruses function differently, as their RNA is reverse-transcribed into DNA, which is integrated into the host cell's genome (when it becomes a provirus), and then undergoes the usual transcription and translational processes to express the genes carried by the virus.
7. dsDNA-RT viruses – double-stranded retroviruses are also called "pararetrovirus.
There is about 10 million viruses in each millilitre of seawater. They infect bacteria, which burst apart and their remains are consumed by other life forms.
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