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In general, the shapes of viruses are classified into four groups: filamentous, isometric (or icosahedral), enveloped, and head and tail. Filamentous viruses are long and cylindrical. Many plant viruses are filamentous, including TMV. Isometric viruses have shapes that are roughly spherical, such as poliovirus or herpesviruses. Enveloped viruses have membranes surrounding capsids. Animal viruses, such as HIV, are frequently enveloped. Head and tail viruses infect bacteria and have a head that is similar to icosahedral viruses and a tail shape like filamentous viruses.

Many viruses use some sort of glycoprotein to attach to their host cells via molecules on the cell called viral receptors ( [link] ). For these viruses, attachment is a requirement for later penetration of the cell membrane, so they can complete their replication inside the cell. The receptors that viruses use are molecules that are normally found on cell surfaces and have their own physiological functions. Viruses have simply evolved to make use of these molecules for their own replication. For example, HIV uses the CD4 molecule on T lymphocytes as one of its receptors. CD4 is a type of molecule called a cell adhesion molecule, which functions to keep different types of immune cells in close proximity to each other during the generation of a T lymphocyte immune response.

 In the illustration a viral receptor on the surface of a KSHV virus is attached to an xCT receptor embedded in the plasma membrane.
The KSHV virus binds the xCT receptor on the surface of human cells. xCT receptors protect cells against stress. Stressed cells express more xCT receptors than non-stressed cells. The KSHV virion causes cells to become stressed, thereby increasing expression of the receptor to which it binds. (credit: modification of work by NIAID, NIH)

Among the most complex virions known, the T4 bacteriophage, which infects the Escherichia coli bacterium, has a tail structure that the virus uses to attach to host cells and a head structure that houses its DNA.

Adenovirus, a non-enveloped animal virus that causes respiratory illnesses in humans, uses glycoprotein spikes protruding from its capsomeres to attach to host cells. Non-enveloped viruses also include those that cause polio (poliovirus), plantar warts (papillomavirus), and hepatitis A (hepatitis A virus).

Enveloped virions like HIV, the causative agent in AIDS, consist of nucleic acid (RNA in the case of HIV) and capsid proteins surrounded by a phospholipid bilayer envelope and its associated proteins. Glycoproteins embedded in the viral envelope are used to attach to host cells. Other envelope proteins are the matrix proteins that stabilize the envelope and often play a role in the assembly of progeny virions. Chicken pox, influenza, and mumps are examples of diseases caused by viruses with envelopes. Because of the fragility of the envelope, non-enveloped viruses are more resistant to changes in temperature, pH, and some disinfectants than enveloped viruses.

Overall, the shape of the virion and the presence or absence of an envelope tell us little about what disease the virus may cause or what species it might infect, but they are still useful means to begin viral classification ( [link] ).

Questions & Answers

what are the biological importance of physical properties of water in human being?
Great Reply
I want more mcqs please
Uday Reply
more what?
Everine
what is meant by the term decarboxylation
Lolem
explain the role natural selection in the evolution of organisms
Lolem
the population produces more than What the environment can support. some organisms adapt well to the environment than others. the less adapted ones disappear leaving the more adapted in the environment.
ATIKPO
What are the Advantage of electron microscope over light microscope?
Liticia Reply
an electronic microscope uses electronic so it's more efficient
Cosmas
It helps to view specimen accurately
ATIKPO
what are nymph nodes?
Lydia Reply
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Martin
because the surface tension is tight like a skin
david Reply
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Lydia
what is genetic
Nad Reply
what is écosystème
Nad
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Nad
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Nad
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Nad
discuss adaptations of flight in birds
Cassim Reply
what is an enzymes
Joseph Reply
mention two types of metabolic
Joseph
what is a cell?
Joseph
is the biological catalyst that speed up chemical reaction in the living thing
Cassim
an enzymes is a biological catalyst that speed up a chemical reaction in living organisms and it is protein in nature
Idah
enzymes are protein that act as biological catalysts
Maria
what agglutriation
Idah
enzymes are biological catalysts that speed up the chemical reactions in a living organism
Ainamani
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Isaac
agglutination is the process by which rhesus factor of blood react during blood transfusion
Paul
Enzymes are biological catalysts, proteins in nature, functioning to increase the rate of chemical reactions and remain unchanged at the end of the reaction.
Everine
Be4 transfusions are performed, a major cross-match made by mixing serum frm the recipient wizblood cells frm the donor.If the types don't match eg if the donor z type A,and recipient z type B,the recipient's antibodies attach 2 the donor's red blood cells and form bridges thatcoz the cells2clump.
Everine
Enzymes are organic catalyst that speeds up the rate or chemical rxn without, being alterect in the process
Henry
an enzyme is a biological catalyst that speed up chemical reactions.
ATIKPO
1.anabolism 2.catabolism
ATIKPO
a cell is the basic functional and structural unit of a living organism.
ATIKPO
what are the two types of sugar contents in carbohydrate?
Jimmy
what is photosynthesis
Conast Reply
photosynthesis is the process by which green plants manufacture their own food from water and carbon dioxide using sunlight as a source of their energy releasing oxygen as a by-product.
Everine
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Nad
what are runners
Godfrey Reply
what is an environment
Bwambale Reply
diagrams are not indicated, why?
Simon Reply
diagrams for what?
Everine
A vaccination is a treatment which makes the body stronger against an infection. The body fights infections using the immune system, which is made up of millions upon millions of cells including T cells and B cells.
Nworie
define the term immunity
Everine
can simply defined as an exemption from an attack
Nworie
is the ability of an organism to resist a particular infection or toxin by a specific antibodies or sensitized white blood cells
Adeb
what is a blood group?
Lydia
A blood group is any different type that human blood can be separated into for medical purposes.
Everine
It is the body ability to resist infection .
ATIKPO
difference between cell and cell membrane
Sunday Reply
cell is a basic unit of living body however cell membrane is a protective layer of cell.
Suhail
very good
Everine
which topic would you like to discuss today?
Everine
vaccine
Nworie
what do you understand by the term vaccine?
Everine
guy I need the answer of this question what occurs during photosynthesis
REAL Reply
Photosynthesis is the process that plants use to convert light into food. During this process, plants create carbohydrates starting with only carbon dioxide and water. Sunlight provides the energy that makes photosynthesis possible.
Stanley
@Stanley,that's how I could as well put it
Evans
what are different between genotype and phenotype
Martha Reply
what is light microscope and electronic microscope
Martha
what occurs during photosynthesis
Martha
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Martha
what is the meaning of computer science
Martha
genotype is the genetical constitution of the gene
Ainamani

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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