INTRODUCTION – What to study

Basic structure and general characteristics of VIRUSES

Investigations Important role they play in the

environment - symbiotic relationships The effect and management of One

disease of Viruses on living organisms Humans use these organisms for a variety

of purposes

VIRUSES

Well-known viruses

HIV ! Avian Flu ! SARS ! Ebola ! West Nile ! Smallpox !Hepatitis A,B,C,D,E ! Polio ! HPV !

HIV-1, SIV and Other RetrovirusesHIV-1, SIV and Other Retroviruses AdenovirusesAdenoviruses

Rhabdoviruses (rabies)Rhabdoviruses (rabies)

Very small between 20 – 450 nm. Made up of a core of DNA or RNA strand/s, which is

enclosed in a protein coat called a capsid. The protein sheath is made up of a number of protein

subunits called capsomeres. Different viruses have different numbers of

capsomeres. Have regular symmetrical shapes, some spherical,

some rod-like, some spiral and some have tails.

Basic structure of viruses

Viruses are non-cellular or acellular because they have no nucleus, ribosomes or mitochondria.

STRUCTURE OF A VIRUS

Not cells [ no nucleus, cytoplasm or organelles]

Have a core of DNA or RNA surrounded by a protein coat [capsid]

Capsid is sometimes covered by an envelope [lipid bilayer] which protects the virus from host enzymes

Basic structure of a virus

Capsid protein

NucleocapsidNaked

capsid virus

DNA

RNA

or =+

NucleocapsidLipid membrane,

glycoproteinsEnveloped virus+

Relative sizes and detection devices

Comparing the size of a virus, a bacterium, and a eukaryotic cell

Viral Size

Millions can fit on pinhead

Smaller than a ribosome!

Basic structure of viruses

Bacteriophages: Viruses that attack bacteria

Come in a variety of shapes Polyhedral Helical Complex

SHAPES OF VIRUSES

Viral structure

TMV Adenovirus Influenza TMV Adenovirus Influenza virus Bacteriophage T4virus Bacteriophage T4

NAKED AND ENVELOPED VIRUSESIcosahedral Helical

Naked capsid

Enveloped

Lipid

Glycoprotein

Matrix

General characteristics of viruses

Have no metabolic or respiratory enzymes and are only active inside host cells

Replicate only inside host cells and are regarded as genetic parasites

They have strands of either DNA or RNA, but never RNA and DNA

Cause a huge variety of plant and animal diseases, such as common cold, influenza, herpes, AIDS

Are absolutely specific with regard to their host, for example the mumps virus lives only in the salivary glands of humans

Viruses reproduce by transforming the host’s nucleic acids into virus nucleic acids when multiplying

SummarySmallest of the germs (can only be seen with an electron microscope)Two states – virus (active) and virion (when dormant)Not living (does not show characteristics of life)Obligate intracellular parasites [can only survive inside the cells of living organisms]Use material of host cells to replicate themselvesCause many fatal diseases in plants and animals

General characteristics of viruses

Can remain in a dormant state within an organism e.g. chicken pox virus (causes

shingles later on in life) or the herpes virus (causes cold

sores)

CHARACTERISTICS OF VIRUSES

GLYCOPROTEINS

Glycoproteins are small molecules found on the outside surface of all body cells. Different types of cells have specific, unique types of glycoproteins attached to them.

Glycoproteins are vital to a number of important biological functions. They allow certain types of cell-to-cell communication, help coordinate complicated cellular responses to stimuli, and activate the action of other types of cells.

THE END