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Past systems of classification

Viruses are classified in several ways: by factors such as their core content ( [link] and [link] ), the structure of their capsids, and whether they have an outer envelope. The type of genetic material (DNA or RNA) and its structure (single- or double-stranded, linear or circular, and segmented or non-segmented) are used to classify the virus core structures.

Virus Classification by Genome Structure and Core
Core Classifications Examples
  • RNA
  • DNA
  • Rabies virus, retroviruses
  • Herpesviruses, smallpox virus
  • Single-stranded
  • Double-stranded
  • Rabies virus, retroviruses
  • Herpesviruses, smallpox virus
  • Linear
  • Circular
  • Rabies virus, retroviruses, herpesviruses, smallpox virus
  • Papillomaviruses, many bacteriophages
  • Non-segmented: genome consists of a single segment of genetic material
  • Segmented: genome is divided into multiple segments
  • Parainfluenza viruses
  • Influenza viruses
Part a (top) is an illustration of the rabies virus, which is bullet-shaped. RNA is coiled inside a capsid, which is encased in a matrix protein-lined viral envelope studded with glycoproteins. Part a (bottom) is a micrograph of a cluster of bullet-shaped rabies viruses. Part b (top) is a micrograph of variola virus, which has DNA encased in a bow-shaped capsid. An oval matrix protein-lined envelope surrounds the capsid. Part b (bottom) shows irregular, bumpy lesions on the arms and legs of a person with smallpox.
Viruses are classified based on their core genetic material and capsid design. (a) Rabies virus has a single-stranded RNA (ssRNA) core and an enveloped helical capsid, whereas (b) variola virus, the causative agent of smallpox, has a double-stranded DNA (dsDNA) core and a complex capsid. Rabies transmission occurs when saliva from an infected mammal enters a wound. The virus travels through neurons in the peripheral nervous system to the central nervous system where it impairs brain function, and then travels to other tissues. The virus can infect any mammal, and most die within weeks of infection. Smallpox is a human virus transmitted by inhalation of the variola virus, localized in the skin, mouth, and throat, which causes a characteristic rash. Before its eradication in 1979, infection resulted in a 30–35 percent mortality rate. (credit “rabies diagram”: modification of work by CDC; “rabies micrograph”: modification of work by Dr. Fred Murphy, CDC; credit “small pox micrograph”: modification of work by Dr. Fred Murphy, Sylvia Whitfield, CDC; credit “smallpox photo”: modification of work by CDC; scale-bar data from Matt Russell)

Viruses can also be classified by the design of their capsids ( [link] and [link] ). Capsids are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex ( [link] and [link] ). The type of genetic material (DNA or RNA) and its structure (single- or double-stranded, linear or circular, and segmented or non-segmented) are used to classify the virus core structures ( [link] ).

The left illustration shows a 20-sided structure with rods jutting from each apex. The right micrograph shows a cluster of adenoviruses, each about 100 nanometers across.
Adenovirus (left) is depicted with a double-stranded DNA genome enclosed in an icosahedral capsid that is 90–100 nm across. The virus, shown clustered in the micrograph (right), is transmitted orally and causes a variety of illnesses in vertebrates, including human eye and respiratory infections. (credit “adenovirus”: modification of work by Dr. Richard Feldmann, National Cancer Institute; credit “micrograph”: modification of work by Dr. G. William Gary, Jr., CDC; scale-bar data from Matt Russell)
Virus Classification by Capsid Structure
Capsid Classification Examples
Naked icosahedral Hepatitis A virus, polioviruses
Enveloped icosahedral Epstein-Barr virus, herpes simplex virus, rubella virus, yellow fever virus, HIV-1
Enveloped helical Influenza viruses, mumps virus, measles virus, rabies virus
Naked helical Tobacco mosaic virus
Complex with many proteins; some have combinations of icosahedral and helical capsid structures Herpesviruses, smallpox virus, hepatitis B virus, T4 bacteriophage

Questions & Answers

what is reproduction
mana Reply
reproduction is the process by which living organisms give rise to young ones of their own kind
Miriam
What is evolution
Wengelawit
the production of new forms of life over time as documented in the fossil record.
mana
hmm
Marvin
give two parasites where secondary host is water snail?
Kevin Reply
what is treats
Raih Reply
what are the organelles in cell that involves in protein sythenis
Rita Reply
what is a melanin?
Judith Reply
what is telophase
Elphas
melanin in that black color we posse in our skins
Marvin
Why do parasites take on a parasitic life?
Asadullah Reply
what is cell
Ousman Reply
A cell is the basic structure unit of an organ
Yaa
what is respiration
Igwe
what is organisms?
Bashir
Organisms are living things that can function on their own
EZEA
A cell is a functional basic unit of an organisms.
Evelyn
Organisms is a entity which consists of one or more cells and are able to undergo all life processes
Evelyn
A respiration is the physical and chemical break down of complex food substance into absorbable or simple form.
Evelyn
What will to a cell if the nucleus is removed..?
Goodrick Reply
When a cell nucleus removed then the cell will not be able to function properly, it will not be able to grow .All the metabolic functioning of the cell will stop .Without nucleus the cell will lose it's control. It can not carry out cellular reproduction .
Evelyn
defin peroxesome
walid
write a short note on how the kidney carry out osmoregulation in man
Rhoda Reply
Kidney play a very large role in human osoregulation by regulating the amount of water reabsorbed from glomerular filtrate in kidney as tubules, which is controlled by hormones such as antrdiuvetic hormone (ADH) , aldosterone and angiotensin.
Evelyn
kidney is capable of osmoregulation in mammal ,
Judith
simple definition for respiratory system
Gift Reply
Respiratory system is a network of organs and tissues that helps you to breathe or help in getting the rids of oxygen and discharge of carbon dioxide in the body.
Ruhiyatu
What are uses of respiratory system
Joster
how it functions
Ousman
what is inresparetion
Fikkabex
Why do parasites take on a parasitic life?
Asadullah
A respiratory system is a biological system consisting of specific organs and structures used for gas exchange in animals and plant
Evelyn
diseases of respiration
walid
when air enters to the body called inresparetion
walid
explain why plants responds to stimuli slowly than animals
Bekoe
how is a aerenchyma tissue adapted to its function
fatuma Reply
Have large air spaces that store air for gaseous exchange... Large air spaces also facilitate bouyancy.
Goodrick
what does DNA mean
innocent Reply
dioxiribo nucleic acid
Lekan
Deoxyribonucleic acid
Goodrick
dioxide nucleic acid
Shadrack
what does RNA mean
Shadrack
Ribonucleic acid
Goodrick
what is DNA and RNA
Miriam
defin work of DNA
walid
what is a zygote
Victor Reply
zygote is developed or fertilized egg cell
Lekan
what is the difference between cell wall and cell membrane
Ruhiyatu Reply
cell wall is found in plant while cell membrane is found in animal cell
Lekan
please this is the main answer to that question okay Cell wall gives shape and support to the cell whiles Cell membrane support the movement of substances into and out of the cell. This question is very tricky that's why I asked.
Ruhiyatu
cell wall makes the cell turgid,in times of flaccidity while cell membrane is a semi permeable tissue
Judith
how cell I form
Elijah Reply

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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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