1. The viral replication cycle consists of 7 stages: attachment, entry, uncoating, transcription/mRNA production, synthesis of viral components, virion assembly, and release. 2. Viruses hijack the host cell's machinery and resources to produce copies of their genetic material and viral proteins. Most steps occur either in the host cell's cytoplasm or nucleus depending on whether the virus contains DNA or RNA. 3. Viruses are classified into 7 categories based on their genome type (DNA or RNA) and replication strategy, such as forming a DNA intermediate or using reverse transcriptase. The classification system provides insight into the diverse mechanisms viruses use to replicate.

1. 1
VIRAL
LIFE
CYCLE
ATTACHMENT
PENETRATION HOST
FUNCTIONS
ASSEMBLY
(MATURATION)
Transcription
REPLICATION
RELEASE
UNCOATING
Translation
MULTIPLICATION
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2. Viral replication is the
formation of
biological viruses during
the infection process in the
target host cells.

3. Viruses must first
get into the cell
before viral
replication can
occur.

4. . Through the generation of abundant copies of
its genome and packaging these copies, the virus
continues infecting new hosts. Replication between
viruses is greatly varied and depends on the type of
genes involved in them.

5. Most DNA viruses
assemble in the nucleus
while most RNA viruses
develop solely in
cytoplasm.

6. Tell me more

7. viruses multiply only in living cells.
The host cell must provide
the energy and synthetic machinery
and the low- molecular-weight
precursors for the synthesis of viral
proteins and nucleic acids

8. The virus replication
occurs in seven stages,
namely
1.Attachment
2.Entry,
3.Uncoating,
4.Transcription / mRNA production,
5.Synthesis of virus components,
6.Virion assembly and
Viral replication of a bacteriophage[3]
7- Release (Liberation Stage).

9. Attachment It is the first step of viral
replication. The virus attaches to the cell
membrane of the host cell. It then injects
its DNA or RNA into the host to initiate
infection..

10. In animal cells these viruses get
into the cell through the process
of endocytosis which works
through fusing of the virus and
fusing of the viral envelope with
the cell membrane of the animal
cell and

11. in plant cells it enters
through the process
of pinocytosis which works
on pinching of the viruses

12. Entry[
The cell membrane of the
host cell invaginates the
virus particle, enclosing it in
a pinocytotic vacuole. This
protects the cell
from antibodies like in the
case of the HIV virus.
Uncoating

13. Uncoating
Cell enzymes
(from lysosomes)
strip off the
virus protein coat.
This releases or
renders accessible
the virus nucleic acid
or genome.

14. Transcription / mRNA production[]
For some RNA viruses, the infecting
RNA produces messenger RNA
(mRNA), which can translate the
genome into protein products.

15. For viruses with negative
stranded RNA, or DNA, viruses
are produced
by transcription then translation.
The mRNA is used to instruct
the host cell to make virus
components. The virus takes
advantage of the existing cell
structures to replicate itself.

16. synthesis of virus components[
The components are manufactured by the
virus using the host's existing organelles:
•Viral proteins: Viral mRNA is translated on
cellular ribosomes into two types of viral
protein:

17. • Structural: proteins which make
up the virus particle
• Nonstructural: proteins not
found in the virus particle,
mainly enzymes for virus
genome replication

18. •Viral nucleic acid (genome
replication): New viral genomes are
synthesized; templates are either the
parental genome or newly formed
complementary strands, in the case of
single-stranded genomes. These
genomes are made by either a
viral polymerase or (in some DNA
viruses) a cellular enzyme, particularly
in rapidly dividing cells.

19. Virion assembly A virion is
simply an active or intact virus
particle. In this stage, newly
synthesized genome (nucleic
acid), and proteins are
assembled to form new virus
particles.
This may take place in the cell's
nucleus, cytoplasm, or
at plasma membrane for most
developed viruses.
Release (liberation stage)

20. Release (liberation stage) The viruses, now
being mature are released by either
sudden rupture of the cell, or gradual
extrusion (force out) of enveloped
viruses through the cell membrane.
The new viruses may invade or attack
other cells, or remain dormant in the
cell.

21. In the case of bacterial viruses,
the release of progeny virions
takes place by lysis of the
infected bacterium. However, in
the case of animal viruses,
release usually occurs without
cell lysis.

22. Viruses are classed into 7 types of
genes, each of which has its own
families of viruses, which in turn have
differing replication strategies
themselves David Baltimore, a Nobel
Prize-winning biologist, devised a
system called the Baltimore
Classification System to classify
different viruses based on their unique
replication strategy. There are seven
different replication strategies based
on this system (Baltimore Class I, II,
III, IV, V, VI, VII). The seven classes of

23. Class 1: Double-stranded DNA
virusesThis type of virus usually must
enter the host nucleus before it is able
to replicate. Some of these viruses
require host cell polymerases to
replicate their genome, while others,
such as adenoviruses or herpes
viruses, encode their own replication
factors.

24. class 2: Single-stranded DNA viruses
Viruses that fall under this category include ones
that are not as well-studied, but still do pertain highly
to vertebrates. Two examples include
the Circoviridae and Parvoviridae. They replicate
within the nucleus, and form a double-stranded DNA
intermediate during replication.

25. Class 3: Double-stranded RNA
viruses
. This class includes two major
families,
the Reoviridae and Birnaviridae.
Replication is monocistronic and
includes individual, segmented
genomes, meaning that each of the
genes codes for only one protein,
unlike other viruses, which exhibit
more complex translation

26. Class 4: Single-stranded RNA
viruses - positive-sense
The positive-sense RNA viruses and
indeed all genes defined as positive-
sense can be directly accessed by
host ribosomes to immediately form
proteins.

27. can be divided into two groups, both of
which replicate in the cytoplasm:
•Viruses
with polycistronic mRNA where the
genome RNA forms the mRNA and is
translated into a polyprotein product
that is subsequently cleaved to form
the mature proteins. This means that
the gene can utilize a few methods in
which to produce proteins from the
same strand of RNA, reducing the size
of its genome.

28. •Viruses with complex transcription,
• for which sub genomic mRNAs,
• ribosomal frameshifting and proteolytic processing of
polyproteins may be used. All of which are different
mechanisms with which to produce proteins from the same
strand of RNA.

29. Class 6: Positive-sense single-
stranded RNA viruses that replicate
through a DNA intermediate
A well-studied family of this class of
viruses include the retroviruses. One
defining feature is the use of reverse
transcriptase to convert the positive-
sense RNA into DNA. Instead of using
the RNA for templates of proteins, they
use DNA to create the templates,
which is spliced into the host genome
using integrase. Replication can then
commence with the help of the host
cell's polymerases

30. class 7: Double-stranded DNA
viruses that replicate through a
single-stranded RNA
intermediateThis small group of
viruses, exemplified by the Hepatitis
B virus, have a double-stranded,
gapped genome that is subsequently
filled in to form a covalently closed
circle (cccDNA) that serves as a
template for production of
viral mRNAs and a subgenomic RNA.
The progenome RNA serves as
template for the viral reverse
transcriptase and for production of the
DNA genome.