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Evolution of viruses

Although biologists have accumulated a significant amount of knowledge about how present-day viruses evolve, much less is known about how viruses originated in the first place. When exploring the evolutionary history of most organisms, scientists can look at fossil records and similar historic evidence. However, viruses do not fossilize, so researchers must conjecture by investigating how today’s viruses evolve and by using biochemical and genetic information to create speculative virus histories.

While most findings agree that viruses don’t have a single common ancestor, scholars have yet to find a single hypothesis about virus origins that is fully accepted in the field. One such hypothesis, called devolution or the regressive hypothesis, proposes to explain the origin of viruses by suggesting that viruses evolved from free-living cells. However, many components of how this process might have occurred are a mystery. A second hypothesis (called escapist or the progressive hypothesis) accounts for viruses having either an RNA or a DNA genome and suggests that viruses originated from RNA and DNA molecules that escaped from a host cell. A third hypothesis posits a system of self-replication similar to that of other self-replicating molecules, likely evolving alongside the cells they rely on as hosts; studies of some plant pathogens support this hypothesis.

As technology advances, scientists may develop and refine further hypotheses to explain the origin of viruses. The emerging field called virus molecular systematics attempts to do just that through comparisons of sequenced genetic material. These researchers hope to one day better understand the origin of viruses, a discovery that could lead to advances in the treatments for the ailments they produce.

Viral morphology

Viruses are acellular    , meaning they are biological entities that do not have a cellular structure. They therefore lack most of the components of cells, such as organelles, ribosomes, and the plasma membrane. A virion consists of a nucleic acid core, an outer protein coating or capsid, and sometimes an outer envelope    made of protein and phospholipid membranes derived from the host cell. Viruses may also contain additional proteins, such as enzymes. The most obvious difference between members of viral families is their morphology, which is quite diverse. An interesting feature of viral complexity is that the complexity of the host does not correlate with the complexity of the virion. Some of the most complex virion structures are observed in bacteriophages, viruses that infect the simplest living organisms, bacteria.

Morphology

Viruses come in many shapes and sizes, but these are consistent and distinct for each viral family. All virions have a nucleic acid genome covered by a protective layer of proteins, called a capsid    . The capsid is made up of protein subunits called capsomeres . Some viral capsids are simple polyhedral “spheres,” whereas others are quite complex in structure.

Questions & Answers

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Sitali Reply
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Sitali
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Memiru
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Rorisang
what is meant by submicroscopic?
anji Reply
what is anabolic and catabolic
Jonathan
hi
Alpha
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Memiru
hallo
Memiru
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Dorathy Reply
biology is scientific study of living things
GUYO
what is chromosomes?
Mabiya Reply
it is a cell structure that contains DNA histones protein and other structural proteins
Ekechi
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Kashah
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Hassan Reply
liver is an organ in the body that meterbolise nutrients and produce bile.
Ekechi
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Gulfam
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Kashah
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Eric Reply
Biology is you
muayad
Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and. evolution
Suzette
biology is the study of living things and none living things
Ekechi
study of living organisms
anji
The mamalian endoskeleton has 206 bones
kaazim Reply
hii
Hannah
hi
Suzette
how you
Hannah
good thanks
Suzette
have you done the actual course?
Suzette
How many bones do human body have?
moses Reply
I don't know please help me
Kisito
206
Waneh
206
Moses
206
anji
what are these geneti materials
ONELIA Reply
Name five parts of female reproductive system and state the function of each part
Angel Reply
What is biology
Angel
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Angel
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ketchem
Ok
Angel
Name five parts of female reproductive system and state the function of each part
Angel
What is the meaning of respiration
Idriss Reply
the act or process of breathing .
Suzette
the process is very long as I know
Idriss
do you want more details ?
Suzette
yes offcourse
Smiso
what does the term diploid and haploid mean?
ONELIA
what is virgina
Shebas Reply
A female reproductive organs
Julius
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Hamis Reply
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Henry Reply
Di= 2cotiledon mono=cotiledon
muayad
Mono = 1 cotiledon
muayad
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Shebas
A Virginia is a part of a female ,the passage of a child during child birth, receiver of the penis and the passage of menstral flow
Idriss
what is biology
Hassan Reply
what is liver
Hassan
Biology is the study of living organisms
Gifty
is the study of life of living organisms
Chansa
study all about organisms like their reproduction, evolution , behaviour Physiology, etc
Ubaid
this is what we call "life"@
Chansa
is the study of living organisms on earth
okubasu
It is the study of living organism
Idriss
Biology is the study of all living organisms
ketchem
what is copulation
ketchem

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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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