Download General Viral Characteristics • Obligate intracellular parasites

General Viral Characteristics
Viral Sizes
• Obligate intracellular parasites.
• Contain either DNA or RNA (not both)
• No ATP-generating mechanisms
• Little to no metabolic activity (produce few to no enzymes)-rely on the metabolic machinery of host cells.
• Acellular (no plasma membrane)
• Small (typical size range = 20 to 1000 nm)
! Largest virus is 14,000 nm (14 µm)
! Chlamydia (obligate intracellular bacterium) is 1000 nm
General Viral Morphology
Bacterial Chromosome
Bacteriophage Lytic Cycle
Nucleic Acid
(RNA or DNA)
Bacterial cell
Bacterial cell
Capsid (protein coat)
Naked Virus
2. Penetration
1. Attachment
Spikes (proteins)
Bacterial cell
3. Biosynthesis
Bacterial cell
Phospholipid Envelope
Enveloped Virus
4. Maturation
Bacterial cell
5. Release
Multiplication Cycle of Animal Viruses
Bacteriophage Lysogenic Cycle
Bacterial Chromosome
Viral
Nucleic
Acid
Naked Virus
Bacterial cell
Prophage
Bacterial cell
2. Penetration
1. Attachment
Lysosome
1. Attachment
Bacterial cell
Enveloped Virus
Many rounds of
bacterial
replication
3. Biosynthesis
Bacterial cell
2. Penetration
3. Uncoating
Viral
Nucleic
Acid
Remnants
of Viral
Capsid
5. Release
Bacterial cell
4. Maturation
Viral envelope melds with host
plasma membrane.
Typical DNA Virus Biosynthesis
1. Attachment 2. Penetration
DNA Virus Families
Viral DNA
Human DNA
3. Uncoating
Release via cell membrane rupturing
(nonenveloped viruses) or budding
(enveloped viruses).
OR
Maturation in nucleus produces
new viral particles
Early genes are transcribed
and translated to produce
proteins needed for
DNA replication.
Viral Family
Size (nm)
Enveloped?
Adenoviridae
70-90
No
None
Upper Respiratory Infections,
Obesity?
Herpesviridae
150-200
Yes
None
Herpes, Cold Sores,
Chickenpox/Shingles,Mononu
cleosis/Burkitt’s Lymphoma
Papovaviridae
40-57
No
None
Warts, Cervical Cancer
200-350
Yes
Viral RNA
polymerase for viral
mRNA production
Smallpox, Cowpox
42
Yes
Reverse Transcriptase Hepatitis B, Liver tumors
reads viral RNA and
produces viral DNA
Poxviridae
Lysogeny (formation of provirus)
Hepadnaviridae
Viral mRNAs are transcribed
in the nucleus (using host
enzymes) and are transported
into the cytoplasm.
Capsid proteins are
translated using host
tRNAs and ribosomes.
Viral Proteases
produced
DNA Replication using host
DNA Polymerase
Viral enzymes
Diseases
+ Strand RNA Virus Families
Biosynthesis of Positive-Strand RNA Viruses
Human DNA
1.
Attachment
2. Penetration
Viral RNA
3. Uncoating
RNA DependentRNA Polymerase
Viral Family
Size (nm)
Enveloped?
Viral enzymes
Picornaviridae
28-30
No
RNA-Dependent RNA
Polymerase
Polio, Hepatitis A, Most
common cause of colds
Flaviviridae
40-50
Yes
RNA-Dependent RNA
Polymerase
Hepatitis C, West Nile
Encephalitis
Calciviridae
35-40
No
RNA-Dependent RNA
Polymerase
Norwalk virus
Most RNA Viruses penetrate into the cytoplasm
Release via cell
membrane rupturing
In POSITIVE-STRAND RNA
(nonenveloped viruses)
VIRUSES, Viral RNA = mRNA
or budding (enveloped
viruses).
Diseases
Capsid proteins are
translated using host
tRNAs and ribosomes.
During maturation,
Viral RNA is packaged
into capsids.
Complementary RNA
is broken down.
Repeated synthesis of
Complementary RNA and
Viral RNA.
- Strand RNA Virus Families
Biosynthesis of Negative-Strand RNA Viruses
Human DNA
Viral RNA
Viral Family
Rhabdoviridae
1.
Attachment
2. Penetration
3. Uncoating
RNA DependentRNA Polymerase
Release via cell membrane
rupturing (nonenveloped Most RNA Viruses penetrate into the cytoplasm
viruses) or budding
(enveloped viruses).
During maturation,
Viral RNA is packaged
into capsids.
Complementary RNA
is broken down.
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Repeated synthesis of
Complementary RNA and
Viral RNA.
In NEGATIVE-STRAND RNA
VIRUSES, COMPLEMENTARY RNA =
mRNA
Filoviridae
Orthomyxoviridae
Size (nm) Enveloped?
Viral enzymes
Diseases
70-80
Yes
RNA-Dependent RNA
Polymerase
Rabies
80-14000
Yes
RNA-Dependent RNA
Polymerase
Ebola
35-40
Yes
RNA-Dependent RNA
Polymerase
Influenza (Fragmented
Genome)
Retroviridae
Biosynthesis of Retroviruses Viruses
Viral Family
Human DNA
Virus with two
identical copies of
RNA and Reverse
Transcriptase enzyme.
1. Attachment 2. Penetration
Release via cell membrane
rupturing (nonenveloped viruses)
or budding (enveloped viruses).
Unc
oati
Retroviridae
Size (nm) Enveloped?
100-120
Yes
Viral enzymes
Reverse Transcriptase
Diseases
AIDS, Adult Leukemia
ng
Maturation in nucleus produces
new viral particles
Reverse Transcriptase makes
viral DNA copy (cDNA)
Viral mRNAs are transcribed
in the nucleus (using host
enzymes) and are transported
into the cytoplasm.
Capsid proteins are
translated using host
tRNAs and ribosomes.
Viral cDNA
integrates into host
chromosome. Other
viral parts digested
away.
Cancer
Cancer = uncontrolled growth of cells. Most cancers are thought to involve multiple
mutations that accumulate sequentially.
1. Tissue made of mass of cells.
2. Random mutation in one cell that
causes loss of control of cell cycle.
3. Mutant cell reproduces faster than
normal cells (so mutant cells pile up).
7. Loss of control leads to
faster cell reproduction
which leads to increasing
rounds of DNA replication
and chance for mutation.
4. Among the mutant cells, one cell
6. One of these cells picks up a
undergoes mutation again in a second
mutation in a third control
control gene causing even more loss
gene.
of control of the cell cycle.
5. The double mutants pile up
even faster.
Viruses and Cancer
The formation of proviruses (lysogeny) represent permanent genetic changes in cells. Thus,
viruses that can form proviruses (DNA and Retroviruses) can cause cancer.
Oncogenes = Genes that increase the rate of cellular reproduction.
Tumor cell transformation:
Dedifferentiated (less specialized than normal body cells)
Transplantable (can detach from one tissue and re-attach to another tissue (can undergo
metastasis)
Loss of contact Inhibition (cancer cells don’t mind being crowded)
Invasive (will squeeze into tight spaces that normal body cells avoid)
Persistent and Latent Viral Infections
Persistent Infections: Slow, but continuously increasing numbers of viral particles in
infected person. May take many months or years for disease to
become apparent (may have no initial acute illness). Example:
HIV, measles, adenovirus diseases.
Latent Infections:
Prions
Infectious, replicable proteins. Prions (PSc) act like enzymes. They bind normal body
proteins (PC) and cause these normal proteins to change shape, becoming prions (PSc).
Normal protein (PC)
is transcribed,
translated, and
displayed on cell
surface.
Infections where viruses are not detectable for long periods of time
but then manifest as a disease. Trigger for disease manifestation is
usually a stressor (infection with another microbe, injury,
psychological stress) of the infected person. Latent infections may
be lysogenic or extrachromosomal. Examples: Herpes, Varicellazoster.
PC
Prions continue
to alter normal
proteins. Some
prions
accumulate in
vesicles.
PSc proteins
binds with
normal
protein.