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By the end of this section, you will be able to:
  • List the steps of replication and explain what occurs at each step
  • Describe the lytic and lysogenic cycles of virus replication
  • Explain the transmission and diseases of animal and plant viruses
  • Discuss the economic impact of animal and plant viruses

Viruses can be seen as obligate, intracellular parasites. A virus must attach to a living cell, be taken inside, manufacture its proteins and copy its genome, and find a way to escape the cell so that the virus can infect other cells. Viruses can infect only certain species of hosts and only certain cells within that host. Cells that a virus may use to replicate are called permissive    . For most viruses, the molecular basis for this specificity is that a particular surface molecule known as the viral receptor must be found on the host cell surface for the virus to attach. Also, metabolic and host cell immune response differences seen in different cell types based on differential gene expression are a likely factor in which cells a virus may target for replication. The permissive cell must make the substances that the virus needs or the virus will not be able to replicate there.

Steps of virus infections

A virus must use cell processes to replicate. The viral replication cycle can produce dramatic biochemical and structural changes in the host cell, which may cause cell damage. These changes, called cytopathic    (causing cell damage) effects, can change cell functions or even destroy the cell. Some infected cells, such as those infected by the common cold virus known as rhinovirus, die through lysis    (bursting) or apoptosis (programmed cell death or “cell suicide”), releasing all progeny virions at once. The symptoms of viral diseases result from the immune response to the virus, which attempts to control and eliminate the virus from the body, and from cell damage caused by the virus. Many animal viruses, such as HIV (human immunodeficiency virus), leave the infected cells of the immune system by a process known as budding    , where virions leave the cell individually. During the budding process, the cell does not undergo lysis and is not immediately killed. However, the damage to the cells that the virus infects may make it impossible for the cells to function normally, even though the cells remain alive for a period of time. Most productive viral infections follow similar steps in the virus replication cycle: attachment, penetration, uncoating, replication, assembly, and release ( [link] ).

Attachment

A virus attaches to a specific receptor site on the host cell membrane through attachment proteins in the capsid or via glycoproteins embedded in the viral envelope. The specificity of this interaction determines the host—and the cells within the host—that can be infected by a particular virus. This can be illustrated by thinking of several keys and several locks, where each key will fit only one specific lock.

This video explains how influenza attacks the body.

Entry

The nucleic acid of bacteriophages enters the host cell naked, leaving the capsid outside the cell. Plant and animal viruses can enter through endocytosis, in which the cell membrane surrounds and engulfs the entire virus. Some enveloped viruses enter the cell when the viral envelope fuses directly with the cell membrane. Once inside the cell, the viral capsid is degraded, and the viral nucleic acid is released, which then becomes available for replication and transcription.

Questions & Answers

what are the example of photosynthesis
Gamshe Reply
Is how plant covert sugar and energy, air and sunlight into energy to grow
Timileyin
My cordial salam to everybody. I have a question to all. What do you mean by plasma membrane?
Mahmud Reply
how alkali metal form
Puskal Reply
what is a cytosol
Siddeeqah Reply
what is cell
Prince Reply
synthesis of 1 molecules of glucose requires
Purvesh Reply
what is the chemical composition of water
Abigail Reply
h20
Rita
Oh, how's is it going..
Brian Reply
not too good
Monique
hy
Adeola
hi
Imamkasim
hi
Veronica
Any one else taking Bio 1406 with Stephanie Martin?
Veronica
where is it ?
ShAmy
am here Veronica
iyota
Part of compound microscope
Bakish Reply
a. body b. stage clip c. adjacent knob d. arm e. eye piece
Kpodo
E
Rita
How do u know when you want to urinate
Akpo Reply
how do you know when you want to urinate
Akpo
I don't know please explain
Coded
As the bladder fills up .. the signals are sent to the brain specifying that its filling up and should be emptied and the fuller it gets, the more signals/ alerts are sent to brain ...leading to the urge to urinate .... to go pee
Khalida
OK thank you
Coded
hello
Issiya
hi
Abigail
wat
Gamshe
I want the this ecologycal terms
Catherine Reply
what are enzymes
Alvin Reply
enzymes are organic catalysts which speed the rate of chemical reaction but it's self is not used up in the process
Azeezah
what are photosynthesis
Gamshe
what are characteristics of photosynthesis
Gamshe
what is fertilization
Ofosu Reply
fusion of male and famele gametes
Biology
fusion of female and male gametes.
Biology
form zygote to eggs
Ahmad
also known as syngamy
RESHMA
why is water called a polar molecule
Jabari Reply
enzyme that not found in mitochondria
Mukesh 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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