Viruses - Viral Infection
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![Page 1: Viruses - Viral Infection](https://reader030.fdocuments.in/reader030/viewer/2022032611/563dbbff550346aa9ab05480/html5/thumbnails/1.jpg)
Envelope
Protein ShellCapsid
Nucleic Acid
Receptors
DNA or RNA
Membrane around virus
Proteins that help virus get into proper host
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Attachment
The virus attaches to
receptors on the host cell.
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The virus is able to get into the cell in one of three ways.
Entry into the Cell
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Fusion of the Membranes
The viral envelope and
cell membrane fuse, allowing
the virus to enter the cell.
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The virus is engulfed by the cell membrane.
Endocytosis
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Injection
E. coli Bacteriophage T4
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What happens once the genetic material is inside the cell?
One of two different processes may occur:
1. The virus takes over the cell and begins to replicate right away, killing the host cell in the process.
2. The virus doesn’t take over or kill the host cell right away, but does begin to replicate.
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Lytic Cycle
There are 5 steps in the Lytic Cycle
RELEASE (LYSIS)
ATTACHMENT
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Lytic Cycle
1. Attachment – the virus attaches to receptors on the host
ATTACHMENT
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Lytic Cycle
2. Penetration – the nucleic acid moves across the cell membrane into the host cell
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Lytic Cycle
3. Replication and Synthesis – the virus degrades the host nucleic
acid and uses the host to make new viral components.
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Lytic Cycle
4. Assembly – viral components are assembled into new viruses.
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Lytic Cycle
RELEASE / LYSIS
5. Release / Lysis – fully assembled viruses are released when the host cell bursts
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Lytic Cycle
Viruses that are in a lytic cycle are described as VIRULENT
RELEASE / LYSIS
ATTACHMENT
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T4 Bacteriophage Lysing E. coli Bacterium
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Bacteriophage Lambda
(λ)
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Lysogenic Cycle
There are 4 steps in the Lysogenic Cycle
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
nnnnnnnnnnnnnnnnndddd
ATTACHMENT
PENETRATION
INTEGRATION
REPLICATION
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Lysogenic Cycle
Steps 1 and 2 are identical to the first two steps in the lytic cycle.
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
nnnnnnnnnnnnnnnnndddd
ATTACHMENT
PENETRATION
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Lysogenic Cycle
INTEGRATION
3. Integration – Phage DNA integrates into bacterial DNA
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Lysogenic Cycle
INTEGRATION
When it becomes integrated into the host DNA, the viral genome is referred to as a PROPHAGE.
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Lysogenic Cycle
REPLICATION
4. Replication – The integrated prophage replicates when bacterial DNA replicates
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Lysogenic Cycle
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
nnnnnnnnnnnnnnnnnd
Viruses that enter into a lysogenic cycle are known as
TEMPERATE VIRUSES
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What is special about Bacteriophage λ?
ATTACHMENT
PENETRATION
REPLICATION AND SYNTHESIS
ASSEMBLY
RELEASE / LYSIS
INTEGRATION
REPLICATION
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Bacteriophage λ attached to an E. coli Bacterium
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Replication of Viral Nucleic Acids
DNA Viruses – replication of viral DNA is similar to the
process that the host cell uses to replicates its own DNA
DNA DNA
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Replication of Viral Nucleic Acids
Most RNA Viruses – replication of viral RNA is dependent upon
an enzyme that is encoded on the viral genome
RNA RNA
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Replication of Viral Nucleic Acids
– RNA viruses that convert their RNA into DNA
using an enzyme that is included with the viral genome
RNA DNA
Retroviruses
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Replication of Viral Nucleic Acids
Retroviruses – This DNA is inserted into the host genome, where it can be transcribed back into viral RNA during normal cellular activity.
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Replication of Viral Nucleic Acids
Retroviruses – Once the DNA is integrated into the host genome, some retroviruses may become LATENT, where they remain
inactive for long periods of time.
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Replication of Viral Nucleic Acids
Human Immunodeficiency Virus (HIV), the virus that causes AIDS, is an example of a retrovirus that
can become latent.
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Retroviruses
Virus hijacks the host cell and keeps making more copies of itself until the host bursts open
Lytic Cycle
Lysogenic Cycle
HIV
Virus integrates into the host genome and replicates when the host divides. When triggered it can enter the lytic cycle.
RNA viruses that convert their RNA to DNA which then integrates into the host genome.
Retrovirus that infects humans which can remain latent for long periods of time.
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HIV Infection
When not active, the virus is described as being latent
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Lytic and Lysogenic Cycles
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Lytic and Lysogenic Cycles
ATTACHMENT
PENETRATION
REPLICATION AND SYNTHESIS
ASSEMBLY
RELEASE / LYSIS
INTEGRATION
REPLICATION
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Lytic Cycle
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Lysogenic Cycle
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Lytic and Lysogenic
Cycles