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