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VIRUSES

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Don Collier Collier

on 9 September 2014

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Transcript of VIRUSES

VIRUSES

insidious genetic information!


Pharoh Ramses V, who died in 1196 BC

History
Characteristics
General Structure
Viral Multiplication

Outline

VIRUS =
POISON, IN LATIN

ORIGINAL USE:

ANYTHING THAT CAUSED DISEASE
I.E., THE VIRUS OF TUBERCULOSIS

EVOLUTION OF THE TERM
GRADUALLY CAME TO MEAN
ANY DISEASE WITH AN UNKNOWN CAUSE

HISTORY

TOBACCO MOSAIC DISEASE

IWANOWSKI FILTERED DISEASED LEAVES AND THE FILTERED MATERIAL DID
NOT CAUSE
DISEASE!

FITRATE (WITHOUT BACTERIA)
DID CAUSE
THE DISEASE!

CONTINUED EVOLUTION OF THE TERM:
FILTERABLE VIRUS;
LATER, “FILTERABLE” WAS DROPPED AND BECAME KNOWN SIMPLY AS VIRUS


DMITRI IWANOWSKI, 1892

MORE MILEPOSTS

FREDERICK TWORT,
1915

DISCOVERED A VIRUS THAT COULD
CAUSE BACTERIA TO DISAPPEAR
CALLED IT BACTERIOPHAGE

BACTERIOPHAGE

SKETCH

ELECTRON MICROGRAPH

T2-bacteriophage
creates a clear zone (plaque) where bacteria infected and lysed by the virus. 
 

VANDERBILT UNIVERSITY
TECHNIQUE TO GROW VIRUSES
ON CHICKEN EMBRYOS WOULD NOT GROW ON ARTIFICIAL MEDIA

EARNEST GOODPASTURE, 1931

Growing Viruses

Chicken embryo after inoculation with
laryngotracheitis virus

SIZE:
SUBMICROSCOPIC

LARGEST
, 250 NM (SMALLPOX)
SMALLEST
, 12 NM (YELLOW FEVER)

DESCRIPTIVE HISTORY:
1930’S

CHEMISTRY: NUCLEI ACIDS AND PROTEINS

ACTUAL FORM VIA ELECTRON MICROSCOPY

Acellular

Alive or Non-living??

ACTIVE / INACTIVE, INSTEAD OF ALIVE OR DEAD

Obligate intracellular parasites




INFECT ALL KINDS OF ORGANISMS

MOST DO NOT CAUSE DISEASE IN HUMANS!


VIRAL FACTS

Description

Comparison of viruses, bacteria, and eukaryotes

Common cold
Measles
Mumps
Warts
Hepatitis
HIV/AIDS

Viral Diseases

CORE
(ALWAYS)
DNA
OR RNA (ALWAYS)

ENZYMES (MAYBE)
COVERING (MAYBE)
CAPSID (OFTEN)
(CAPSOMERES, CAPSID SUBUNITS)
ENVELOPE (MAYBE)
SPIKES (MAYBE)

Virus components

Components
Persistent fever
Unusual cancers
Diarrhea
Neurological disorders
Life-threatening opportunistic infections

AIDS symptoms when T-cell count < 200/mm3)

RNA genome

Retrovirus:
produces Reverse Transcriptase

Codes the RNA genome into a DNA molecule (RNA --> DNA)
Allows the virus to incorporate into the host DNA

HIV Characteristics

Both cycles, side by side
(two slides)

COMPUTER VIRUS:
named for cell virus
Insidious Information with a latent period

Similar process to lytic EXCEPT:
no immediate replication of new viruses
viral nucleic acid is incorporated into host DNA
each time the host cell divides, viral DNA is replicated along with host DNA

May resume lytic cycle at any time
CAUSES LYSIS AT AN UNPREDICTABLE TIME
LIKE A COMPUTER VIRUS!

Lysogenic or latent Infection

Lytic
virus multiplies and destroys the host cell

Lysogenic or latent
viral DNA incorporated into host DNA

Types of Viral Infections

Tuberculosis
Pneumonia
Candidiasis
Herpes
Toxoplasmosis
Histoplasmosis
Others

Some Common Opportunistic Infections in AIDS

I. Acute disease: Flu-like symptoms, weeks to months. Antibodies formed (Usually within 6-8 weeks)


II. Asymptomatic: May persist years


III. Persistent Generalized Lymphoadenopathy (continued swelling of lymph nodes for more than 6 months)

Disease Progression of HIV

Agent of disease is
Human Immunodeficiency Virus

Latter stages of infection with HIV called AIDS

AIDS:
Acquired Immunodeficiency Syndrome

HIV/AIDS

HIV / AIDS

COPYING:
Replication, Transcription and Protein Syntheisis

Virus components inside host cell
are
put together
to form new virus particles

Hundreds of new viruses made inside single host cell. Some animal viruses cause production up to 100,000 viruses

Maturation

Lysogenic cycle

Lytic cycle

Host cells without cell walls
(animal cells)
entire virus enters host cell by endocytosis or fusion,
(Trojan Horse method)

Host cells with cell walls:

Viral nucleic acid injected into cytoplasm
Uses virus enzymes


Penetration

Adsorption

Penetration

Copying
(Replication, transcription and synthesis of viral protein)

Maturation

Release

Acrostic:
(A Puppy Chews Many Rugs)

The viral cycle

Rupture of host cell
Budding (exocytosis)

Release

Molecules on virus surface

Match

Molecules on host cell surface (receptors)

Result: virus-host specificity

Adsorption

Aids
Viral
cycle

Viral
multiplication


ORIGINS
MOMENT OF SILENCE FOR A VIRUS?
Hypothesis 1:
descendents of cells that were parasites inside other cells
Hypothesis 2:
genetic elements of cells that escaped from cells
Hypothesis 3:
arose independently from replicating molecules that preceded cells


Hypothesis 2 is the least cumbersome of these guesses

Speculation on Origin of Viruses

Viruses are a biological enigma. They are noncellular, and therefore they do not fit into current classification systems, which are devoted to categorizing the cellular organisms on Earth. 2 Mader 310
some scientists are beginning to think viruses may have been the first to utilize DNA as their genetic material. In that case, we owe them a word of thanks for originally creating the molecule we and most organisms use as their genetic material. 2 Mader 316
http://t1.gstatic.com/images?q=tbn:ANd9GcQ5ABGvpGObDO9wIrQPBv7K8lZscLzS9_BOR3ojNX6jApKavl1-Ow
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