Draw the basic structure of a virus Label and define capsid viral envelope and nucleic acid Ch 17 Warmup Draw the lyticlysogenic cycle What stage of the lyticlysogenic cycle is a virus virulent Temperate ID: 793684
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Slide1
Ch. 17 Warm-up
Why do many scientists classify viruses as non-living?
Draw the basic structure of a virus. Label and define capsid, viral envelope and nucleic acid.
Slide2Ch. 17 Warm-up
Draw the lytic/lysogenic cycle.
What stage of the lytic-lysogenic cycle is a virus virulent? Temperate?
What determines a host range?
Slide3Viruses
Chapter 17
Slide4What you must know:
The components of a virus.
The differences between lytic and lysogenic cycles.
How viruses can introduce genetic variation into host organisms.
Mechanisms that introduce genetic variation into viral populations.
Slide5Bacteria vs. Viruses
Bacteria
Virus
Prokaryotic cell
Most are free-living (some parasitic)
Relatively large size
Antibiotics
used to kill bacteria
Not a living cell (genes packaged in protein shell)
Intracellular parasite
1/1000 size of bacteria
Vaccines
used to prevent viral infection
Antiviral treatment
Slide6Viruses
Very small (<ribosomes)
Components =
nucleic acid
+
capsid
Genetic material
:
DNA or RNA (double or single-stranded)
Capsid
: protein shell
Some viruses also have
viral envelopes
that surround capsid
Slide7Viruses
Limited
host range
Entry = attach to host cell membrane receptors through capsid proteins or glycoproteins on viral envelope (animal)
Eg
. human cold virus (rhinovirus)
upper respiratory tract (mouth & nose)
Reproduce quickly within
host cells
Can mutate easily
RNA viruses: no error-checking mechanisms
Slide8Slide9Slide10Slide11Simplified viral replicative cycle
Slide12Video: t4 Phage infection
Slide13Viral Reproduction
Lytic
Cycle:
Use host machinery to
replicate, assemble, and release copies of virus
Virulent phages
:
Cells die
through
lysis
or
apoptosisLysogenic (Latent) Cycle:
DNA incorporated into host DNA and replicated along with itBacteriophage DNA =
prophage
Animal virus DNA =
provirus
UV radiation, chemicals: lysogenic
lytic cycle
Temperate Phage
: uses both methods of replication
Slide14Bacteriophage
Virus that infects bacterial cells
Slide15Lytic Cycle of T4 Phage
Slide16Lytic Cycle vs. Lysogenic Cycle
Slide17Bacterial defenses against phages:
Natural selection
: bacterial surface proteins mutate and prevent phage entryRestriction enzymes
: destroy foreign DNA
CRISPR-Cas9 system
: enzymes that identify and cut invading phage DNA
The CRISPR system = bacterial
immune system
Slide18Animal viruses
have a membranous
envelope
Host membrane forms around exiting virus
Difficult for host immune system to detect virus
Slide19Video: How Dengue Virus enters a cell
Slide20Retrovirus
RNA virus that uses
reverse transcriptase
(RNA template
DNA)
Newly made viral DNA inserted into chromosome of host
(
provirus
)
Host transcribes provirus to make new virus parts
Example: HIV (Human Immunodeficiency Virus)
Slide21HIV = Retrovirus
Slide22Origin: Chimpanzee virus
Infects white blood cells (helper T)
HIV+
:
provirus (DNA inserted), latent
AIDS
: <200 WBC count, opportunistic infections
HIV:
Slide23Video: HIV Life Cycle
Slide24Other Human Viruses
Herpes virus
Smallpox
Herpes Simplex Virus 1 (HSV-1)
Herpes Simplex Virus 2 (HSV-2)
Eradicated in 1979 due to worldwide vaccination campaigns
Slide25Ted-Ed: How we conquered the deadly smallpox virus
Slide26RNA viruses = High mutation rates
Slide27Emerging Viruses
Ebola Virus
H1N1 Influenza A Virus
West Nile Virus
Zika
Virus
Viruses that suddenly become apparent
Caused by existing viruses (combo of viruses)
Human diseases can originate from animals
Slide28Current Outbreaks
Zika
Virus
Measles Virus
Epidemic
:
widespread outbreak
Pandemic
:
global outbreak
Chikungunya
Virus
Slide29Slide30Drugs for Prevention/Treatment
Vaccine
: weakened virus or part of pathogen that triggers immune system response to prevent infection
Ex. HPV, MMR, HepA, Flu shot
Antiviral Drugs
: block viral replication after infection
Ex. Tamiflu (influenza), AZT (HIV)
Slide31Slide32Plant Viruses
Similar structure and mode of replication as animal viruses
Horizontal transmission
: infected by outside source
Vertical transmission
: inherited from parent
No cures for most viral plant diseases
Eg
. t
obacco mosaic virus (TMV)
Slide33Prions
Misfolded, infectious
proteins
that cause misfolding of normal proteins
Eg. scrapie (sheep), mad cow disease (BSE), Creutzfeldt-Jakob disease (humans), kuru (humans – New Guinea)
Slide34Diseases caused by
prions
Prions act slowly – incubation period of at least 10 years before symptoms develop
Prions are virtually indestructible (cannot be denatured by heating)
No known cure for prion diseases
Kuru in New Guinea
Slide35Prion Neurodegenerative Diseases
Alzheimer’s Disease
Parkinson’s Disease
Slide36Amoeba Sisters: Viruses: Virus replication and the mysterious common cold