Transcript Viruses - Mr. Jones Jaguars

Viruses
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Biology:
Kingdoms Research Project
Mr. Jones
EM of Enveloped Virus with receptor molecules
Viruses: Overview & Concepts
Structure
 Adaptations
 Reproduction &
Development
 Diversity
 Phylogeny
 Importance

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TEM: Ebola Virus
Definition: Virus
 Sub
microscopic entity consisting of
a single nucleic acid (N.A)
surrounded by a protein coat, or
capsid, capable of replication only
within a living host.
 Obligate Intracellular Parasite
Are Viruses Alive?

Characteristics of life
 What Viruses Don’t...
– Respire (produce energy)
– Metabolize (make biological molecules)
– Grow & Develop

What Viruses Do...
– Reproduce- obligate to a host
– Adapt/Evolve- change through time
Viral Morphology (Structure)

Basic Structure: 2 principle structures
– Protein Capsid
• Outer covering protecting core & giving shape
– Inner Nucleic Acid Core (RNA or DNA)
• Used in viral classification
– *Envelope or Lipoprotein Coat
• Enveloped viruses- similar to their eukaryotic
host cell’s plasma membrane
• Not present in all viruses
Basic Enveloped Viral Structure
Lipid Envelope
Protein
Capsid
Virion
Associated
Polymerase
(enzyme)
Nucleic Acid
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Influenza Virus following
lytic cycle
Receptor
Molecules
Structure:
Capsid Protein Arrangement

Protein Arrangement Determines:
– 1. Viral shape- images on next slide
•
•
•
•
Polyhedral (HPV, Polio, Adenovirus)
Helical (Tabacco Mosiac Virus)
Enveloped (Influenza, HIV)
Binal (baceriophages)
– 2. What host a virus can infect
– 3. Method virus will infect host
Typical Viral Shapes
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Viral Size

Extremely Small...
– most range 5nm-300nm
– as small as ribosomes
– between 4-900 genes

Yet Complex...
– Icosahedrals like polio &
adenoviruses can have up to
20 symmetrical sides
Learn more in the Class Project
DYK?- 1 drop of blood can contain as many as
6 billion viruses!
Bacteriophages infect bacteria
Virus Classification

Classified by Shape & Nucleic Acid Class
 DNA viruses – stable, do not mutate as
rapidly
– Single-stranded or double-stranded
– Smallpox, Hepatitis B

RNA viruses – mutate rapidly, unstable
– Single-stranded or double-stranded
– HIV, Rhinovirus (common cold)
Viral Classification Chart
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Naming Viruses

Once named by...
– Common names such as...
• Diseased they cause (rabies, poliovirus)
• Organ or tissue they infect (adenovirus: from
adenoid tissue where common cold is found)

Universal System(s)
– Families with Genus name + “virus” &
species name + “viridae” (herpesviridae)
Bacteriophases invading E.coli
Viral Adaptations
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
Viruses evolve quickly
 Have several methods of infecting a host
 Viruses can survive for long periods of time
both inside & outside of a host
 Recognition & Attachment
– Virus receptor molecule to cell receptor site
– Viral species are specific to host
• Smallpox- affects only humans
• Polio- affects only certain human nerve cells
Viral Adaptations

Transmission
– Air, fluids (blood, fecal, sexual), animal vectors
(insects, mice, monkeys)

Methods of entering & leaving host
– Direct attachment to receptor molecule
(Polyhedral viruses)
– Endocytosis with cell membrane (Enveloped
viruses)
– Attachment by tail fibers (Binal viruses)
Viral Reproduction

Reproductive Overview: A Virus...
– infects a host through a reception
mechanism
– alters host ribosomes, DNA, or RNA
– uses host metabolism to replicate N.A.
• Host cell makes & assemble new viruses
• Host cell lyses (burst) leading to cell death
– All host cell’s eventually enter a Lytic Cycle
Viral Reproduction Diagram
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Viral Diversity
There are 22 classes of bacteria.
 400 identified plant viruses causing up
to 1,000 identified diseases
 Eastimated:

– 1000’s of animal viruses causing as many
as 10,000 diseases
– 1031 bacteriophages on Earth alone
Viral Diversity

Reproductive Cycles
– Lytic & Lysogenic Cycles

Provirus
– viral DNA integrated into host DNA
– remains dormant or inactive

Retroviruses
– contain enzyme reverse transcriptase
• RNA is transcribed into DNA (ex. HIV)
Lytic Cycle
Virus attaches to host cell’s membrane
and injects its nucleic acid into the host
cell.
 The viral nucleic acid takes over protein
synthesis, creating new viruses.
 The host cell lyses releasing the newly
formed viruses.
 Cycle repeats exponentially

Before attachment
Attachment/Reception
Cell lyses
Penetration of N.A.
Replication of viral
proteins
Viral assembly
Lysogenic Cycle
Viral N.A. are integrated into host’s DNA
becoming a provirus
 Provirus is replicated with host cell
replication (mitosis)
 Infect cell’s turn lytic, killing host cells
 Lysogenic Cycle Video

– http://www.youtube.com/watch?v=_J9xKitsd0
Lysogenic Cycle
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Adaptations- Comparing Cycles

Lytic
– Kills host cells
– Mutates quickly &
ramdomly
• Often without benefit
to the virus
– Rapid
• Typical lytic cycle- 30
minutes to produce
200 viruses

Lysogenic, Provirus, &
Retrovirus
– Uses cell’s reproduction
& lysis
– NA integration into cell
DNA
– remain dormant for
periods of time
– Slower
• High transmission rate
• Slower but more
effective mutation
Viral Phylogeny
Viruses likely evolved from the host
themselves
 Some may have evolved in protists
such as amoebas
 HIV phylogeny & evolution

– Emergent Viruses- host to human
HIV Phylogeny- SIV to HIV
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Importance

Viruses drive evolution
– Adapted organisms survive
– Controls populations
– Mutate genetics of host
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• Both for the good & bad

Gene Therapy & Viral Vectors
– Using viruses to transmit healthy genes to people
with genetic disorders & diseases
Importance

No Cure- most drugs affect enzymes, cell
membranes, or reproductive cycle; virus have
almost none of these traits
 Vaccines & immunization
– Cowpox & Smallpox (eradicated)

HIV can infect 10 billion cells per day, the
body can only replace 1.8
 AIDS Prevalence
– http://www.avert.org/worldstats.htm
– http://kwanzaakeepers.com/africa-aids-deathcount/africa-aids-death-count.htm
• One sub-Saharan African is infected with HIV every 9
seconds. One person dies from AIDS every 13 seconds.