Post on 03-Jan-2016
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Viruses
Biology:
Kingdoms Research Project
Mr. Jones
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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
Nucleic Acid
Receptor Molecules
ProteinCapsid
Lipid Envelope
VirionAssociatedPolymerase(enzyme)
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Influenza Virus following lytic cycle
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 ProjectDYK?- 1 drop of blood can contain as many as6 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)
Viral Adaptations
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
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Bacteriophases invading E.coli
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
Cell lyses
Before attachment
Attachment/Reception
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=_J9-xKitsd0
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
• Both for the good & bad
Gene Therapy & Viral Vectors– Using viruses to transmit healthy genes to people
with genetic disorders & diseases
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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-death-count/africa-a
ids-death-count.htm• One sub-Saharan African is infected with HIV every 9 seconds. One
person dies from AIDS every 13 seconds.