Virology Lecture Slide 1

What is a virus?Lecture 1

Biology W3310/4310Virology

Spring 2013“There is an intrinsic simplicity of nature and the ul5mate contribu5on of science resides in the discovery of unifying and simplifying generaliza5ons, rather than in the descrip5on of isolated situa5ons -‐ in the visualiza5on of simple, overall pa<erns rather than in the analysis of patchworks”

-‐-‐SALVADOR LURIA

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Biology W3310/W4310Virology

• Prof. Vincent Racaniello, Ph.D.

-‐ [email protected]

-‐ twiHer.com/@profvrr

-‐ Google+ gplus.to/profvrr

• Prof. Saul Silverstein, Ph.D.

-‐ [email protected]

• TAs: Ashlee BenneH, Stephanie Sarbanes, Katharina Shaw

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• courseworks.columbia.edu

-‐ Schedule, readings, screencasts, grading

• virology.ws/course

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Textbook: Principles of Virology, Third EdiUon, ASM Press

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• virology blog: www.virology.ws

• This Week in Virology: www.twiv.tv

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• Weekly quiz

• 3 exams

• Discussion sessions (W4310 only)

• Extra credit

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• Office hours: Thursdays 4-‐6 PM, HHSC 1310B, 701 W. 168th (Medical Center)

• Skype: profvrr

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We live and prosper in a literal cloud of viruses

• Viruses infect all living things

• We eat and breathe billions of virions regularly

• We carry viral genomes as part of our own geneUc material

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More than 1030 bacteriophage parUcles in the world’s waters!

• A bacteriophage par2cle weighs about a femtogram (10-‐15 grams)

1030 X 10-‐15= the biomass on the planet of BACTERIAL VIRUSES ALONE exceeds the biomass of elephants by more than 1000-‐fold!

•The length of a head to tail line of 1030 phages is more than 200 million light years!

hBp://www.phagehunter.org/2008/09/how-‐far-‐do-‐those-‐phages-‐stretch.html

The number of viruses on Earth is staggering

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Andromeda Galaxy -‐ 2.5 million light years away

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There are ~1016 HIV genomeson the planet today

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How ‘infected’ are we?

• HSV-‐1, HSV-‐2, VZV, HCMVEBV, HHV-‐6, HHV-‐7, HHV-‐8

• Once infected, it is for life

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You are a reservoir for viruses that have set up residence in your lungs, gastrointesJnal tract

and other places

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Amazingly, the vast majority of the viruses that infect us have liNle or no impact on our health or well

being

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Not all viruses make you sick...

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The good viruses

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Viruses are amazing

This course will teach you why and how

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•This course is designed to help you see the ‘big picture’ of virology

•I’ll show you how to think about virology as an integraUve discipline, not an isolated collecUon of viruses, diseases, or genes

•You will learn the fundamentals about these molecular wizards that amaze the informed and frighten the uninformed

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What is a virus?

• An infec5ous, obligate intracellular parasite

• Package genome in a parUcle for transmission from host to host

• Viral genome contains informaUon to iniUate and complete an infecUous cycle within a cell

• All viral genomes are able to establish themselves in a host populaUon so that viral survival is ensured

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Are viruses alive?

hHp://www.virology.ws/are-‐viruses-‐alive/

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The virus and the virion

A virus is an organism with two phases

virion infected cell32

As virions are obligate molecular parasites, every soluUon must reveal something about the host as well as the virus

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Be careful: Avoid anthropomorphic analyses

Viruses do NOT think!(or employ, ensure, exhibit, display, etc...)

They do not achieve their goals in a human-‐centered manner

They survive because they make huge numbers of mutants, and selecUon removes the ill-‐adapted

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E. coli

Carbon atom

myosin ac2n

Viruses are very small

100,000x

1,000,000x

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How many viruses can fit on the head of a pin?

• 500 million rhinoviruses

• When you sneeze, you fire an aerosol that contains enough viruses to infect thousands

2 mm = 2000 microns

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Mimivirus parJcles can be seen bylight microscopy

giantvirus.org38

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Viruses replicate by assembly of pre-‐formed components into many

parJcles

Not binary fission like cells

Make the parts,assemble the final product

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• EsUmates of molecular evoluUon place some viruses among the dinosaurs

• Likely evolved much earlier

How old are viruses?

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Ancient references to viral diseases

1580-‐1350 B.C.700 B.C.

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• PrevenUon of virus infecUons in pracUce since the 11th century without knowledge of agent

• Survivors of smallpox protected against disease

• Variola5on -‐ inoculaUon of healthy individuals with material from a smallpox pustule (Lady Montagu)

• 1790s -‐ experiments by Edward Jenner in England establish vaccinaJon

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Concept of microorganisms

• Leeuwenhoek (1632 -‐ 1723)

• Pasteur (1822 -‐ 1895)

• Koch (1843-‐1910)

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Virus discovery -‐ filterable agents

• 1892 -‐ Ivanovsky

• 1898 -‐ Beijerinck: contagium vivum fluidum

• virus: slimy liquid, poison

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Virus discovery

• 1898 -‐ Loeffler & Frosch -‐ agent of foot & mouth disease is filterable

• Key concept: agents not only small, but replicate only in the host, not in broth

• 0.2 micron filters (µm, one millionth of a meter)

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Virus discovery

• 1901 -‐ first human virus, yellow fever virus

• 1903 -‐ rabies virus

• 1906 -‐ variola virus

• 1908 -‐ chicken leukemia virus, poliovirus

• 1911 -‐ Rous sarcoma virus

• 1915 -‐ bacteriophages

• 1933 -‐ influenza virus48

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We know many details about viruses

Chemical formula for poliovirus: C332,652 H492,388 N98,245 O131,196 P7,501 S2,340

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Virus classificaJon

• Nature and sequence of nucleic acid in virion

• Symmetry of protein shell (capsid)

• Presence or absence of lipid membrane (envelope)

• Dimensions of virion & capsid

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Virus classificaJon

Classical hierarchical system:

Kingdom

Phylum

Class

Order (-‐virales)

Family (-‐viridae)

Genus (-‐virus)

Species

Filoviridae (filovirus family)

Ebolavirus

Zaire ebolavirus

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• 40,000 virus isolates from bacteria, plants, animals placed in 6 orders, 87 families, 349 genera, 2284 species.

• BUT -‐ there are 1030 virions in the oceans!

hHp://ictvonline.org/

ICTV

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Analyzed DNA from Lake Limnopolar, AntarcUca. Found 10,000 species, from 12 different families,

some completely new.

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Raw sewage harbors diverse viral populaJons

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There is an underlying simplicity and order to viruses because of two simple

facts

• All viral genomes are obligate molecular parasites that can only funcUon aser they replicate in a cell

• All viruses must make mRNA that can be translated by host ribosomes: they are all parasites of the host protein synthesis machinery

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Documents

Virology Lecture Slide 1