They however try to carry a small baggage when traveling and use the host cell machinary to produce stuff that they need along the way.
A virus is a submicroscopic parasitic particle that infects cells in biological organisms. The study of viruses is virology.
Viruses are obligate intracellular parasites that lack the cellular machinery for self-reproduction. Viruses infect eukaryotes and prokaryotes such as bacteria; viruses infecting prokaryotes are also known as bacteriophages or phages. Typically viruses carry a small amount of genetic material, either in the form of DNA or RNA, but not both, surrounded by some form of protective coat consisting of proteins, lipids, glycoproteins or a combination. The viral genome codes for the proteins that constitute this protective coat, as well as for those proteins required for viral reproduction that are not provided by the host cell.
Viruses are non-living particles that can only replicate when an organism reproduces the viral RNA or DNA. Viruses are considered non-living by the majority of virologists because they do not meet all the criteria of the generally-accepted definition of life. Among other factors, viruses do not move, metabolize, or decay on their own. However, a comprehensive definition of life is still somewhat elusive since some bacteria (considered living) like rickettsia exhibit both characteristics of living and non-living particles.
Because viruses are acellular and do not have their own metabolism, they must utilize the machinery and metabolism of the host for the purpose of self-replication. Before a virus has entered a host cell, it is called a virion — a package of viral genetic material. Virions can be passed from host to host either through direct contact or through a vector, or carrier. Inside the organism, the virus can enter a cell in various ways. Bacteriophages—bacterial viruses—attach to the cell wall surface in specific places. Once attached, enzymes make a small hole in the cell wall, and the virus injects its DNA into the cell. Other viruses, such as HIV, enter the host via endocytosis, the process by which cells take in material from the external environment. After entering the cell, the virus's genetic material begins the destructive process of causing the cell to produce new viruses.
There are three different ways genetic information contained in a viral genome can be reproduced. The form of genetic material contained in the viral capsid, the protein coat that surrounds the nucleic acid, determines the exact replication process.
Some viruses have DNA which is replicated by the host cell along with the host's own DNA.
There are two different replication processes for viruses containing RNA. In the first process, the viral RNA is directly copied using an enzyme called RNA replicase. This enzyme then uses that RNA copy as a template to make hundreds of duplicates of the original RNA. A second group of RNA-containing viruses, called the retroviruses, uses the enzyme reverse transcriptase to synthesize a complementary strand of DNA so that the virus' genetic information is contained in a molecule of DNA rather than RNA. The viral DNA can then be further replicated using the resources of the host cell.
Bacteriophages have two cycles called the lytic cycle and lysogenic cycle. In the lytic cycle the host cell undergoes lysis (the breaking open of the cell to release viral particles), biosynthesis, maturation and finally release. In the lysogenic cycle viral replication does not immediately occur, but replication may take place some time in the future. some viruses e.g. lambda are capable of carrying out both cycles. In the lytic cycle the cell is soon destroyed and the viruses made will have to find new host. However during the lysogenic stage the DNA of the bacteria is spliced using restriction enzymes and the virus's DNA (or RNA turned to DNA by the enzyme reverse transcriptase) is integrated into the spliced section of the hosts DNA. The virus remains dormant but after the host cell has replicated many times the virus will become active and will enter the lytic phase. The lysogenic cycle allows the host cell to continue to survive and reproduce. As the host reproduces with the virus embedded in its genome, the virus itself is reproduced as a byproduct. Therefore many progeny cells containing the virus develop.
Viral populations do not grow through cell division (local doubling), but instead each infected cell becomes a virus factory that is capable of producing thousands of copies of the invading viruses.
Attachment, sometimes called adsorption: The virus attaches to receptors on the host cell wall.
Injection: The nucleic acid of the virus moves through the plasma membrane and into the cytoplasm of the host cell. The capsid of a phage, a bacterial virus, remains on the outside. In contrast, many viruses that infect animal cells enter the host cell intact.
Transcription: Within minutes of phage entry into a host cell, a portion is transcribed into mRNA, which is then translated into proteins specific for the infecting phage.
Replication: The viral genome contains all the information necessary to produce new viruses. Once inside the host cell, the virus induces the host cell to synthesize the necessary components for its replication.
Assembly: The newly synthesized viral components are assembled into new viruses.
Release: Assembled viruses are released from the cell and can now infect other cells, and the process begins again.
When the virus has taken over the cell, it immediately causes the host to begin manufacturing the proteins necessary for virus reproduction. Some viruses, like herpes, cause the host to produce three kinds of proteins: early proteins, enzymes used in nucleic acid replication; late proteins, proteins used to construct the virus coat; and lytic proteins, enzymes used to break open the cell for viral exit. The final viral product is assembled spontaneously, that is, the parts are made separately by the host and are joined together by chance. This self-assembly is often aided by molecular chaperones, or proteins made by the host that help the capsid parts come together.
The new viruses then leave the cell either by exocytosis or by lysis. Envelope-bound animal viruses cause the host's endoplasmic reticulum to make certain proteins, called glycoproteins, which then collect in clumps along the cell membrane. The virus is then discharged from the cell at these exit sites, referred to as exocytosis. On the other hand, bacteriophages must break open, or lyse, the cell to exit. To do this, the phages have a gene that codes for an enzyme called lysozyme. This enzyme breaks down the cell wall, causing the cell to swell and burst. The new viruses are released into the environment, killing the host cell in the process.
More info at
http://en.wikipedia.org/wiki/Viruses Yes. They have RNA. They do. Look at the number of babies born with Human immunodeficiency virus. If the mother has the virus, it will naturally pass to the baby, because the baby grows inside the woman's uterus and shares her blood supply.
It's too bad, but that's the way life is. DEE! DEE! DEE! OR COUSE YOU IDOT Yes, they do. yes they have hereditary materials .either of them RNA or DNA can be there hereditary material Some viruses have RNA, others have DNA
More Questions & Answers...
- what is the theory of realitivity?
- How would hypothermia affect blood flow?
- PLEASe hellp! me!! physics homework :'(?
- i am having trouble remembering things i study for school.how can i remember things?
- What are some Austrian dances, literature, traditional dress and national sports?