A virus is a nonliving particle made of nucleic acid and a protein coat. In 1935, Wendell Stanley crystallized the tobacco mosaic virus. However, it still remained infectious, so scientists concluded that they were not made of cells. Viruses are not alive because they lack some key characteristics of living organisms. Viruses do not have cytoplasm or organelles. They cannot carry out metabolism or homeostasis. They cannot reproduce outside their host cell. Viruses consist of a protein coat, capsid, which, in some cases, is the only layer of protection for the virus. Some viruses capsids are helicle, polyhedral, and others are encased in a bilipid layer membrane called an envelope. These tend to be spherical. Viruses can be classified by whether they have RNA or DNA in their genome, whether it is double or single stranded, or its linear or circular.
Viruses first need to recognize a host cell before they can infect it. They use the receptors on cell membranes to identify cells. Viruses are obligate intracellular parasites—they replicate only by using the host cell. When the DNA of a virus enters a host cell, it makes mRNA. The DNA of the other viruses enters the chromosome. This inserted viral DNA is called a provirus. The virus then uses the cell to make new viral parts. Some virus DNA serves as RNA, which is transcribed and used. Some RNA viruses, called retroviruses, use Reverse transcriptase. It uses RNA to make DNA, which it then inserts into cell DNA. HIV is a retrovirus. Bacteriophages are viruses that infect bacteria. They have complex capsids made of a hexagonal head filled with DNA. Attached to the head is a protein tail with 1 or more tail fibers. These fibers attach to cells and help the virus inject its DNA into the cell. They reproduce by one or both reproductive processes: the lytic cycle or the lysogenic cycle. Lytic Cycle- quick infection and destruction
Viruses that only use this cycle are called virulent.
First, a virus injects its DNA into a cell. Then, the ends of the viral DNA attach to each other and make a circle. The viral DNA takes control of the cell and the viral DNA is copied. Enzymes transcribe mRNA from the viral DNA. Then, head proteins are made that contain viral DNA. Finally, lysosomes digest the cell wall (lysis) and the up to 200 bacteriophages spread. Lysogenic Cycle- Slower, allow viruses to stay dormant
A virus who uses this cycle is called temperate.
First, the virus injects its DNA into the cell. The viral DNA integrates with the cell DNA, creating a prophage (section of Viral DNA in the host cells DNA). The bacteria replicates, and the viral DNA spread. After as many replications as are needed have completed, the cell can enter the lytic cycle.
Viruses can be used to duplicate genes for high demand genes for study, such as the cystic fibrosis gene. Scientists believe that viruses evolved from early cells. Viruses are an example of natural selection because only the strongest influenza viruses that can fight off the human resistance survive.
24.2 Viral Disease
A vector is an intermediate host that transfers a pathogen or a parasite to another organism. [For example, the mosquito is the vector of the West Nile Virus] Chickenpox and Shingles
Both of these diseases are called by a herpes virus. The virus multiplies and travels to blood vessels in the skin, causing rashes. After being infected, a person has lifelong resistance. The virus can sometimes stay within a person and cause shingles later on. Viral Hepatits
Hepatitis is an inflammation of the virus spread by at least 5 viruses, A-E, transmitted through contaminated food and water, sexual contact, contact with infected blood and serum, and contaminated needles. Acquired Immune Deficiency Syndrome (AIDS)
HIV is spread by sexual contact; contact with infected body fluids like blood, semen, or vaginal fluids, and from mother to fetus. Glycoproteins on the surface of HIV bond to receptors on macrophages, which are white blood cells. First the virus attaches to the receptors. Then it realeases its capsid into the host cell, where viral RNA and reverse transcriptase are released. The HIV DNA inserts itself into the cell DNA, becoming a provirus. Eventually, the infected cells go through the lytic cycle and break out. Scientists have tried to make medicine that inhibits the ability of reverse transcriptase. Other medicines block the synthesis of capsids. These medicines are called protease inhibitors. Viruses and Cancer
Some viruses contain oncogenes, genes that cause cancer by blocking normal cell reproduction. Other viruses can cause cancer because the viral DNA inserts itself into a host’s chromosome near a proto-oncogene, which usually controls cell growth. These cell turn into viral oncogenes. Emerging diseases are illeness caused by new or reappearing infectious agents that typically exist in animal populations. Closeness with animals has led to human diseases like SARS, Ebola, and Hantavirus. In the countries where these are most prevalent, vaccines are usually too expensive for the general public. A vaccine is a solution that contains a harmless version of a pathogen. An inactivated virus cannot replicate. An attenuated virus is a weakened virus. Usually, attenuated viruses serve as better vaccines because the body produces more antigens. The World Health Organization successfully eradicated natural smallpox through vaccination and quarantines. An important part of controlling viruses is to control the vectors that spread them. Vaccines are sometimes given to wild animals. There are not many antiviral drugs that can successfully block virus DNA without hurting the body.
24.1 Viral Structure and Replication
A virus is a nonliving particle made of nucleic acid and a protein coat. In 1935, Wendell Stanley crystallized the tobacco mosaic virus. However, it still remained infectious, so scientists concluded that they were not made of cells. Viruses are not alive because they lack some key characteristics of living organisms. Viruses do not have cytoplasm or organelles. They cannot carry out metabolism or homeostasis. They cannot reproduce outside their host cell. Viruses consist of a protein coat, capsid, which, in some cases, is the only layer of protection for the virus. Some viruses capsids are helicle, polyhedral, and others are encased in a bilipid layer membrane called an envelope. These tend to be spherical. Viruses can be classified by whether they have RNA or DNA in their genome, whether it is double or single stranded, or its linear or circular.
Viruses first need to recognize a host cell before they can infect it. They use the receptors on cell membranes to identify cells. Viruses are obligate intracellular parasites—they replicate only by using the host cell. When the DNA of a virus enters a host cell, it makes mRNA. The DNA of the other viruses enters the chromosome. This inserted viral DNA is called a provirus. The virus then uses the cell to make new viral parts. Some virus DNA serves as RNA, which is transcribed and used. Some RNA viruses, called retroviruses, use Reverse transcriptase. It uses RNA to make DNA, which it then inserts into cell DNA. HIV is a retrovirus.
Bacteriophages are viruses that infect bacteria. They have complex capsids made of a hexagonal head filled with DNA. Attached to the head is a protein tail with 1 or more tail fibers. These fibers attach to cells and help the virus inject its DNA into the cell. They reproduce by one or both reproductive processes: the lytic cycle or the lysogenic cycle.
Lytic Cycle- quick infection and destruction
Viruses that only use this cycle are called virulent.
First, a virus injects its DNA into a cell. Then, the ends of the viral DNA attach to each other and make a circle. The viral DNA takes control of the cell and the viral DNA is copied. Enzymes transcribe mRNA from the viral DNA. Then, head proteins are made that contain viral DNA. Finally, lysosomes digest the cell wall (lysis) and the up to 200 bacteriophages spread.
Lysogenic Cycle- Slower, allow viruses to stay dormant
A virus who uses this cycle is called temperate.
First, the virus injects its DNA into the cell. The viral DNA integrates with the cell DNA, creating a prophage (section of Viral DNA in the host cells DNA). The bacteria replicates, and the viral DNA spread. After as many replications as are needed have completed, the cell can enter the lytic cycle.
Viruses can be used to duplicate genes for high demand genes for study, such as the cystic fibrosis gene. Scientists believe that viruses evolved from early cells. Viruses are an example of natural selection because only the strongest influenza viruses that can fight off the human resistance survive.
24.2 Viral Disease
A vector is an intermediate host that transfers a pathogen or a parasite to another organism. [For example, the mosquito is the vector of the West Nile Virus]
Chickenpox and Shingles
Both of these diseases are called by a herpes virus. The virus multiplies and travels to blood vessels in the skin, causing rashes. After being infected, a person has lifelong resistance. The virus can sometimes stay within a person and cause shingles later on.
Viral Hepatits
Hepatitis is an inflammation of the virus spread by at least 5 viruses, A-E, transmitted through contaminated food and water, sexual contact, contact with infected blood and serum, and contaminated needles.
Acquired Immune Deficiency Syndrome (AIDS)
HIV is spread by sexual contact; contact with infected body fluids like blood, semen, or vaginal fluids, and from mother to fetus. Glycoproteins on the surface of HIV bond to receptors on macrophages, which are white blood cells. First the virus attaches to the receptors. Then it realeases its capsid into the host cell, where viral RNA and reverse transcriptase are released. The HIV DNA inserts itself into the cell DNA, becoming a provirus. Eventually, the infected cells go through the lytic cycle and break out. Scientists have tried to make medicine that inhibits the ability of reverse transcriptase. Other medicines block the synthesis of capsids. These medicines are called protease inhibitors.
Viruses and Cancer
Some viruses contain oncogenes, genes that cause cancer by blocking normal cell reproduction. Other viruses can cause cancer because the viral DNA inserts itself into a host’s chromosome near a proto-oncogene, which usually controls cell growth. These cell turn into viral oncogenes.
Emerging diseases are illeness caused by new or reappearing infectious agents that typically exist in animal populations. Closeness with animals has led to human diseases like SARS, Ebola, and Hantavirus. In the countries where these are most prevalent, vaccines are usually too expensive for the general public. A vaccine is a solution that contains a harmless version of a pathogen. An inactivated virus cannot replicate. An attenuated virus is a weakened virus. Usually, attenuated viruses serve as better vaccines because the body produces more antigens. The World Health Organization successfully eradicated natural smallpox through vaccination and quarantines. An important part of controlling viruses is to control the vectors that spread them. Vaccines are sometimes given to wild animals. There are not many antiviral drugs that can successfully block virus DNA without hurting the body.