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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 is the instrument used for measuring water potential?
Agyeiwaa Reply
tensiometers
osometer
MP
difference between food chain and food web
tunz Reply
is the study of living
Cabdi Reply
ohh ok..
HAMIDAH
hys
Cabdi
tro or right
Cabdi
yeah u re right, study of living
HAMIDAH
ok dear
Cabdi
aha
HAMIDAH
hee maxaa kwda hee
Cabdi
what is biology
Sandra Reply
Biology is the natural science that studies life n living organisms which include physical structures, chemical processes, molecular interaction, physiological mechanisms, evolution n development
HAMIDAH
biology is d study of living things
tunz
tru
Cabdi
brnch of biology
Cabdi
biology is the study of living things
tunz
hy hamidah
Cabdi
biology is the study of living things
Nikolas
main branch re botany, zoology n micro biology
HAMIDAH
1.Biochemistry 2.Biophysics 3.Biotechnology 4.Botany 5.Cell biology 6.Ecology
Peace
Main branch of biology are,zoology, botany and microbiology
Agyeiwaa
the period of cell growth between nuclear division
AAYAT Reply
what is synapsis
Edward Reply
the fusion of chromosomes at yhe the beginning of meiosis
Hassan
what do we mean by the team genetic
Regina Reply
is the inheritance of the living organisms
Sarah
am I right?
Sarah
is the variation and inheritance of living organism
Raymond
genetic is define as the scientific study of heredity and variation in living things
HAMIDAH
give all the characteristics of an enzyme
Davies Reply
it alters the rate of chemical reaction
tunz
-some require coenzymes -they re inhibited by inhibitors -they re required in minute amount -they speed up the rate of chemical reaction
HAMIDAH
hi Hamida, may I ask how do you study bio?
al
thanks
al
what is the difference between meiosi and
Glory Reply
TCRs. in full. and was it all about .Tell me about all of immunity.
KIIZA Reply
why is it that, when using light microscope for viewing the red blood cell is not distinguishable
Samuel Reply
Hello guy what is happening
Glory Reply
what is a cell
Innocent Reply
basic unit of life
Adoma
smallest unit of living things
Nicholas
cell is a basic unit of life
Senamile
the fundamental and structural unit of a living organism
angelina
what will happen if cytokenesis did not occurs during meiosi
Senamile Reply
hi
Samuel
The daughter cell would not separate from the parent cell.
Eric
it will separate when it matured
Oberdy
Really then what is the process
Samuel
what is a cell
Innocent
a cell is the basic unit of life
Samuel
what is the function if subcutaneous fat in the skin
Adoma
what is an endospermous seed
Glory
it served as a passageway for nerves and blood vessels between the skin and the muscle
Glory
that is for subcutaneous fat in the skin oo
Glory
Chromosomes are duplicated during what stage of cell cycle
Marsha
what are organic and inorganic fertilizer
Afia
the separation that exist between the parent cell and the daughter cell won't occur
Opoku
what is the function of a nucleus
Japheth 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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