Virology lecture 2 (viral structure)

Marilen M. Parungao-Balolong

Reference: Chapter 3 Carter And Saunders, 2007)

VIRAL STRUCTURE & CLASSIFICATIONS144 Lecture 2 (Virology)

http://www.virology.ws

Thursday, June 30, 2011



winfoin.com

SKILLS, VALUES, OUTPUTS

✤ Listening, Writing and Oral Communication Skills

✤ Critical Analysis and Organization of Ideas

✤ Appreciate Importance of Viral Structure

Marilen M. Parungao-Balolong 2011 Reference: Chapter 3 Carter And Saunders, 2007)


LECTURE OUTLINE

✤ Recall: Viruses Introduction

✤ Structure of Viruses

✤ Functional Anatomy

✤ Classification



REFERENCES

✤ Carter and Saunders, 2007 (Chapter 3)

✤ Gelderblom, 2010 (Chapter 41)

✤ (Bookshelf ID: NBK8174 PMID: 21413309)

✤ http://www.ncbi.nlm.nih.gov/books/NBK8174/



http://www.ncbi.nlm.nih.gov/pubmed/21413309

http://www.ncbi.nlm.nih.gov/pubmed/21413309

http://www.ncbi.nlm.nih.gov/books/NBK8174/

http://www.ncbi.nlm.nih.gov/books/NBK8174/

LECTURE OUTLINE




✤ Classification



VIRUSES: INTRODUCTION

✤ Viruses are small obligate intracellular parasites

✤ Contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat



VIRUSES: INTRODUCTION

✤ Viruses may be viewed as mobile genetic elements, most probably of cellular origin and characterized by a long co-evolution of virus and host


bio3400.nicerweb.net


VIRUS: INTRODUCTION

✤ Propagation depend on specialized host cells supplying the complex metabolic and biosynthetic machinery of eukaryotic or prokaryotic cells


ncbi.nlm.nih.gov


LECTURE OUTLINE




✤ Classification


virology.ws

medical-dictionary.thefreedictionary.com


dvm5.blogspot.com

Reference: Chapter 3 Carter And Saunders, 2007)

Marilen M. Parungao-Balolong 2011


CORONAVIRUS STRUCTURE: SARS


http://learn.genetics.utah.edu/archive/sars/index.html




THE CORE: GENOME

✤ Except in helical nucleocapsids, little is known about the packaging or organization of the viral genome within the core

✤ SMALL VIRIONS:

✤ simple nucleocapsids

✤ containing 1 to 2 protein species


Copyright © 1996, The University of Texas Medical Branch at Galveston.


http://www.ncbi.nlm.nih.gov/books/about/copyright/


THE CORE: GENOME

✤ LARGE VIRIONS:

✤ nucleic acid genome complexed with basic protein(s)

✤ protected by a single- or double layered capsid or by an envelope






CHEMICAL COMPOSITION OF GENOME

✤ The genome of a virus may consist of DNA or RNA, which may be single stranded (ss) or double stranded (ds), linear or circular

✤ The entire genome may occupy either one nucleic acid molecule (monopartite genome) or several nucleic acid segments (multipartite genome)

✤ The different types of genome necessitate different replication strategies



INTRODUCTION TO VIRUS STRUCTURE

✤ TYPES OF VIRION STRUCTURE


TYPES GENOMESGENOMESGENOMESGENOMES

dsDNA ssDNA dsRNA ssRNA

Icosahedral (naked)

Icosahedral (Enveloped)

Helical (naked)

Helical (Enveloped)



http://www.mansfield.ohio-state.edu/~sabedon/017vrgnm.gif




VIRUS GENOMES

✤ dsDNA✤ encode their genes in the same kind of

molecule as animals, plants, bacteria and other cellular organisms

✤ ssDNA, dsRNA, ssRNA✤ unique to viruses



ARRANGEMENT OF GENOME


GENOME EXAMPLEssDNA, linear ParvovirusdsDNA, linear Poxvirus

ssDNA, circular Phage X174dsDNA, circular Baculoviruses

ssRNA, linear Tobacco Mosaic VirusdsRNA, linear Reovirus

ssRNA, circular Hepatitis D virus

Note: there are no viruses known with circular dsRNA genomes


USUALLY....

✤ FUNGI VIRUSES

✤ dsRNA

✤ PLANT VIRUSES

✤ ssRNA

✤ PROKARYOTIC VIRUSES

✤ dsDNAMarilen M. Parungao-Balolong 2011 Reference: Chapter 3 Carter And Saunders, 2007)

sdnhm.org

http://www.whmsoft.net

topnews.in






POINTS TO REMEMBER...

✤ Some linear molecules may be in a circular conformation as a result of base pairing between complimentary sequences at their ends

✤ Example:✤ DNA in Hepadnavirus✤ RNA in Influenza virions



virology.ws


medical-dictionary.thefreedictionary.com

Take note of the nucleocapsid and envelope

THE CAPSID: PROTEIN CORE



THE CAPSID: PROTEIN CORE

Structure of adenovirus. The icosahedral capsid structure of adenovirus is made up of three proteins, hexon, penton base, and fiber. A cross-sectional view of the viral capsid. Some proteins are associated with viral DNA, whereas others are associated with hexon and are involved in the formation of the capsid.


MORPHOLOGY : Helical

✤ Helical morphology is seen in nucleocapsids of many filamentous and pleomorphic viruses

✤ Helical nucleocapsids consist of a helical array of capsid proteins (protomers) wrapped around a helical filament of nucleic acid


The helical structure of the rigid tobacco mosaic virus rod






✤ In the replication of viruses with helical symmetry, identical protein subunits (protomers) self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path

✤ Nucleocapsids form rigid, highly elongated rods or flexible filaments




✤ Details of the capsid structure are often discernible by electron microscopy

✤ NOTE: Helical nucleocapsids are characterized by length, width, pitch of the helix, and number of protomers per helical turn


Fragments of flexible helical nucleocapsids (NC) of Sendai virus, a paramyxovirus, are seen either within the protective envelope (E) or free, after rupture of the envelope





MORPHOLOGY

✤ Icosahedral morphology is characteristic of the nucleocapsids of many “spherical” viruses



MORPHOLOGY

✤ Lines through opposite vertices define axes of fivefold rotational symmetry: all structural features of the polyhedron repeat five times within each 360° of rotation about any of the fivefold axes

✤ Lines through the centers of opposite triangular faces form axes of threefold rotational symmetry; twofold rotational symmetry axes are formed by lines through midpoints of opposite edges.


Icosahedral models seen, left to right, on fivefold, threefold, and twofold axes of rotational symmetry





MORPHOLOGY

✤ Viruses were first found to have 532 symmetry by x-ray diffraction studies

✤ Electron microscopy with negative-staining techniques


Adenovirus after negative stain electron microscopy





MORPHOLOGY

✤ PROTOMERS:

✤ structural polypeptide chains

✤ arranged in oligomeric clusters (capsomeres)

✤ readily delineated by negative staining electron microscopy

✤ form the closed capsid shell


Adenovirus after negative stain electron microscopy





THE CAPSOMERES


pc.maricopa.edu


CAPSOMERES & ENVELOPE

✤ The number and arrangement of the capsomeres are useful in identification and classification

✤ Many viruses also have an outer envelope


Envelope of Herpesvirus

biologie.uni-hamburg.de


CAPSID & ENVELOPE


pc.maricopa.edu



THE ENVELOPE

✤ Envelope consists of a lipid bilayer with proteins (usually glycoproteins) imbedded in it

✤ Lipids derived from host cell

✤ Proteins encoded by the virus

✤ Envelope is important in determining host cell specificity & some aspects of cell penetration are affected by it



ENVELOPED VIRUSES



COMPLEX VIRUSES


LECTURE OUTLINE




✤ Classification


bbc.co.uk


STRUCTURE IN RELATION TO FUNCTION

✤ Core

! ! ! a.! DNA or RNA

! ! ! b.! Contains genetic

information

! !


ncbi.nlm.nih.gov



✤ Capsid

! ! ! a.! Outer protein coat

! ! ! b.! Functions

! ! ! ! 1).!Protects core

! ! ! ! 2).!Shape of the virus

! ! ! ! 3).!Attachment to host

cell membrane (by means of

spikes)Marilen M. Parungao-Balolong 2011 Reference: Chapter 3 Carter And Saunders, 2007)

sparknotes.com

library.thinkquest.org



✤ Envelope

✤ Membrane around capsid - enveloped virus

✤ Not all viruses have envelope

✤ If lack envelope - naked virus!

✤ Composed of:

✤ Bilayer of phospholipids and proteins

✤ Derived from host bell membrane during viral multiplicationMarilen M. Parungao-Balolong 2011 Reference: Chapter 3 Carter And Saunders, 2007)

microscopicblog.blogspot.com



✤ Functions :

✤ Protection from drying (enhances transmission)

✤ Makes virus more susceptible to chemical agents that dissolve lipids

✤ Attachment to host cell membrane (by means of spikes)


wpro.who.int

me-you-and-virus.blogspot.com


LECTURE OUTLINE




✤ Classification



✤ Viruses are grouped on the basis of size and shape, chemical composition and structure of the genome, and mode of replication



PLANT VIRUSES

Marilen M. Parungao-Balolong 2011 Reference: Chapter 13 TortoraMicrobiology


CLASSIFYING ENVELOPED VIRUS BASED ON SHAPE...

✤ Sphere (eg. Influenza virus)

✤ Bullet (e.g. Rabies virus)

✤ Rod (e.g. Baculovirus)

✤ Thread (e.g Ebola virus)



CLASSIFYING VIRUS BASED ON GENOME...


antiviralintelistrat.com


Date

END OF LECTURE 2



Virology lecture 2 (viral structure)

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Transcript of Virology lecture 2 (viral structure)