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Replication and assembly

The replication mechanism depends on the viral genome. DNA viruses usually use host cell proteins and enzymes to make additional DNA that is transcribed to messenger RNA (mRNA), which is then used to direct protein synthesis. RNA viruses usually use the RNA core as a template for synthesis of viral genomic RNA and mRNA. The viral mRNA directs the host cell to synthesize viral enzymes and capsid proteins, and assemble new virions. Of course, there are exceptions to this pattern. If a host cell does not provide the enzymes necessary for viral replication, viral genes supply the information to direct synthesis of the missing proteins. Retroviruses, such as HIV, have an RNA genome that must be reverse transcribed into DNA, which then is incorporated into the host cell genome. They are within group VI of the Baltimore classification scheme. To convert RNA into DNA, retroviruses must contain genes that encode the virus-specific enzyme reverse transcriptase that transcribes an RNA template to DNA. Reverse transcription never occurs in uninfected host cells—the needed enzyme reverse transcriptase is only derived from the expression of viral genes within the infected host cells. The fact that HIV produces some of its own enzymes not found in the host has allowed researchers to develop drugs that inhibit these enzymes. These drugs, including the reverse transcriptase inhibitor AZT    , inhibit HIV replication by reducing the activity of the enzyme without affecting the host’s metabolism. This approach has led to the development of a variety of drugs used to treat HIV and has been effective at reducing the number of infectious virions (copies of viral RNA) in the blood to non-detectable levels in many HIV-infected individuals.

Egress

The last stage of viral replication is the release of the new virions produced in the host organism, where they are able to infect adjacent cells and repeat the replication cycle. As you’ve learned, some viruses are released when the host cell dies, and other viruses can leave infected cells by budding through the membrane without directly killing the cell.

Art connection

The illustration shows the steps of an influenza virus infection. In step 1, influenza virus becomes attached to a target epithelial cell. In step 2, the cell engulfs the virus by endocytosis, and the virus becomes encased in the cell’s plasma membrane. In step 3, the membrane dissolves, and the viral contents are released into the cytoplasm. Viral mRNA enters the nucleus, where it is replicated by viral RNA polymerase. In step 4, viral mRNA exits to the cytoplasm, where it is used to make viral proteins. In step 5, new viral particles are released into the extracellular fluid. The cell, which is not killed in the process, continues to make new virus.
In influenza virus infection, glycoproteins attach to a host epithelial cell. As a result, the virus is engulfed. RNA and proteins are made and assembled into new virions.

Influenza virus is packaged in a viral envelope that fuses with the plasma membrane. This way, the virus can exit the host cell without killing it. What advantage does the virus gain by keeping the host cell alive?

Watch a video on viruses, identifying structures, modes of transmission, replication, and more.

Different hosts and their viruses

As you’ve learned, viruses are often very specific as to which hosts and which cells within the host they will infect. This feature of a virus makes it specific to one or a few species of life on Earth. On the other hand, so many different types of viruses exist on Earth that nearly every living organism has its own set of viruses that tries to infect its cells. Even the smallest and simplest of cells, prokaryotic bacteria, may be attacked by specific types of viruses.

Questions & Answers

diagram of Prokaryotic cells
Magreth Reply
where is it?
Yazi
ʜɪ
Malikie
ʜɪ
Malikie
where is the diagram?
Yazi
waiting.....
Yazi
what
Malikie
good morning guyz
Joelia
gd morning
Hannalyn
morning how are u doing
Paul
doing all fyn en u
Joelia
👍👍👍
Gruxz
morning everyone.. by is Grace we have be saved... Ephesians 2:8....
Cosmo
what is a cell of a bacteria called
Sahfe Reply
what is genotype
James
genotype: this is the combination of alleles an organism has for a given characteristic..
Cosmo
what is maiotic
Gabriel Reply
what is sexual reproduction
Gabriel
what are the effects of concentration gradient in the uptake of water by plant's
Harleen Reply
ls it ok if you have sex during pregnancy
Kags Reply
no
Bernard
yes!!!
Yazi
Yes
Babie
hello
Cabdi
Babie Maseuse .. Hello .. how are you ?
kf
yes it make the baby's strength stay longer
REAL
Who are you?
Babie
why not it's nicer and more enjoyable more than ok for the woman
Lamin
danso from the Gambia and you why do you ask
Lamin
as long as the woman is comfortable and in any possible position good for her
Lamin
unless medically advised to stop or hault and those conditions are also applicable to certain problem in pregancies. Pls any further comment pls never hesitate to ask
Lamin
how tell us
Tony
an assignment for you pls
Lamin
it's recommended
Nyakato
Hello
george
hi how are you?
Lamin
Fine
george
hello everyone
Cosmo
Good night to everyone am from Zambia may the Grace of the Lord be with you all
Cosmo
u too hv gd dreams
Joelia
thanks colleagues and wish you all the best insha Allah
Lamin
InshaAllah
Joelia
Marsha Allah
Lamin
yes
James
What is the meaning of organ
Ronald Reply
tissue combined to form organ
zameer
join
Elishs
orga- these are tissues join together to perform a specific functions.
Elishs
then what are tissues
Kags
group of cells working together to perform a particular function
Harleen
tissue are group of cells put together to perform a certain goal
Bernard
What will happen when read blood cell placed in 0.5 % Nacl solution
zameer Reply
what is biology
Tariro Reply
biology is the study of living organisms
Bernard
examply is the study of.
Nantamu
biology is the study of life.
Nantamu
what is biology
Francis Reply
kidny with large and and many glomeruli are characcteristic feathure of ?
zameer
Can you please put up the notes for antibiotics
Jesus Reply
I can't
Francis
we should first know what is antibiotics.what is antibiotics.
Francis
A cell is the basic functional unit of life.
Jael
what is a cell ?
Rabecca Reply
A cell is the basic functional unit of all organisms
Glandwell
A cell is a basic functional and structural unit of life.
Mavis
please, emphasize more on the coronary circuit
Toyyiba Reply
define the photosynthesis
Sabrinah Reply
list the type of protein
Sabrinah
sugar.glucose
Tamirat
renin,pepsin
Nyakato
peptides
Nyakato
what is photosynthesis
Francis
what is biology
Nathan Reply
branch of science which deal with living and non living things
zameer
different branches of biology
linus
zameer is right
Onuoha
we don't study non living things in biology
mejury
biology is simply the study of life
Toyyiba
biology can simply be the branch of science that deals with the study of flora and fauna
Nyakato
Biology is the study of life
Peace
What is Diffusion
Soliu
The word "Bio" means life and "Logy" means study or knowlegde". Biology is the study of Life (living organisms from microorganisms to plant and animals), their behaviour, mode of living, actions, e.t.c
adewunmi
Bio means life and logy means study of so in other words Biology means study of life
Peace
what is zameer
Francis
what is biology
Pamodou Reply
is the study of life
George
Biology is the study of life
Peace
the word "Bio" is the greek word for "Life" while "Logy" is the knowledge, study of Life. Therefore, Biology is the study or knowledge of life in which case can be from micro organism to plants to animals, their mode of life, features, characteristics, survival e.t.c
adewunmi
biology is the study of living organisms
mejury
study of living organisms
Moses

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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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