Virus - Veni, Vidi, Vici ?

Izabela Tworowska, PhDDepartment of Biochemistry and Cell Biologyizabela7@rice.edu

Part I

Viruses - structure 1. contain nucleic acid, either DNA or RNA (but not both), and a protein coat (encases the nucleic acid). 2. some viruses enclosed by an envelope of fat and protein molecules.

• The smallest virus: satellite tobacco necrosis virus (STNV) plant virus, not enveloped; 17 nm in diameter; consists of 60 protein subunits and RNA; Satellite virus- depends on co-infection with the helper virus (providing missing replication function)

Animal (human) satellite virus: Hepatitis delta virus (HDV) cannot survive w/o the helper virus Hepatitis B virus (HBV)

Capsid the protein shell that encloses the nucleic acid; capsid + nucleic acid = nucleocapsid three functions: nucleic acids protected from digestion by enzymes contains special sites (spikes) on its surface (attach to a host cell) provides proteins allowing the virus to penetrate the host cell

Envelope glycoprotein envelope surrounds the nucleocapsid; composed of two lipid layers; glycoprotein’s spikes on the envelope

Nucleic Acids few groups of viruses use DNA; most are single-stranded RNA viruses; RNA viruses may contain:

plus strand RNA – direct synthesis (translation) of viral protein

negative strands RNA- first synthesis messenger RNA , then viral protein synthesis

VIRUS- where, why, how ?

. Occupy the “gray area” between living and non-living organisms

Speculated form of proto-life (unlikely that they preceded cellular life during the Earth's early evolution). . Viruses started as rogue segments of genetic code

(adapted to a parasitic existence)

How do they replicate?

Cannot survive without a host cell synthesize proteins,

generate or store energy in the form of the adenosine triphosphate (ATP)

Where do they come from?

Complementary Strand (mirror strand)

Viruses can have different genomes

Herpes simplex Polio, HIV, Influenza Reovirus

HBV -partially ss, mainly dsDNA

Eryhtrovirus

HIV

The relative size of some viruses

http://www.usq.edu.au

The relative size of some viruses –how big?

http://www.usq.edu.au

NOBODY IS SAFE !

Viruses can infect animals, plants, or bacteria. (viruses cannot penetrate plant cell walls, plant viruses are transmitted by insects or other organisms)

Classification of viruses into families:type and size of their nucleic acid,

size and shape of the capsid presence of the envelope Bacterial virus

T4 Bacteriophage

Shapes of viral capsid

rods, filaments spheres head- tail structure Tobacco mossaic virus Hepatitis B T4 bacteriophage Enterobacteria phage Polio virus

the simplest way to arrange non-symmetrical icosahedral symmetry, components and place in circle to form discs. (20 triangular facets )

Advantage of the subunits structure of the viruses: greater genetic stability

1. the virus attaches to the target cell

2. the viral nucleic acids enters the cell

3. the host cell synthesizes the proteins encoded in the viral genome and replicates the virus’s DNA or RNA

4. the new viral proteins and the nucleic acids assemble into new viruses

5. the new viruses are released from the cell

Virus life cycle

HIV life cycle

Guess, who am I ? Virion , Viroid or Prion ?

Virion virus infective form (outside the cell) contains at least one unique protein synthesized by specific genes in its nucleic acid.

Viroid (meaning "virus-like") disease-causing organism contains only nucleic acid and has no structural/functional proteins

Prion ("virus-like") composed primarily of a ‘’infectious agent’’ – protein Spongiform encephalopathies

The infectious agent (protein) has been called a prion.

A prion has been defined as "small proteinaceous infectious particles which resist inactivation by procedures that modify nucleic acids". The discovery that proteins alone can transmit an infectious disease has come as a considerable surprise to the scientific community.

The Prion Hypothesis

from Corey Wilson’s lecture

Spongiform Encephalopathies

Disease and accurance Host Date

Scrapie (Several countries eg. UK) Sheep 1936

Transmissible Mink Encephalophathy (TME) Mink 1956

Kuru (people New Guinea) Humans 1966

Creutzfeld-Jacob Disease (Uniform world-wide incidence), 1 per million per annum

Humans 1968

Bovine Spongiform Encephalopathy (BSE)

Cattle 1988

Feline Spongiform Encephalopathy (FSE) Domestic cat 1991

US Pavilion at Expo '67, by Buckminster Fuller and Shoji Sadao, at Montreal, Canada, 1967.

Buckminster Fuller (1893-1983) architect, mathematician

invented the geodesic dome

http://www.greatbuildings.com/architects/Fuller_and_Sadao.html

Buckminsterfullerene, C60, the molecule that started it all.

(eta2-C70-Fullerene)-carbonyl-chloro-bis(triphenylphosphine)-iridium

J.Am.Chem.Soc., 113, p8953,1991

FULLERENES (BUCKYBALL)

The Royal Swedish Academy of Sciences has awarded the 1996 Nobel Prize for Chemistry jointly to:

•Professor Robert F. Curl, Jr., Rice University, Houston, USA

•Professor Sir Harry W. Kroto FRS, University of Sussex, Brighton, UK •Professor Richard E. Smalley, Rice University, Houston, USA

for their discovery of fullerenes

DNA buckyballs

DNA buckyballs used for drug delivery as containers for chemical reactions

Science News, August 29, 2005

• See next on Thursday!