INTRODUCTION – What to study

1. 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

2. VIRUSES Well-known viruses HIV ! Avian Flu ! SARS ! Ebola ! West Nile !Smallpox ! Hepatitis A,B,C,D,E ! Polio !HPV !

3. HIV-1, SIV and Other Retroviruses Adenoviruses Rhabdoviruses (rabies)

4. Viruses are non-cellular or acellular because they have no nucleus, ribosomes or mitochondria. Basic structure of viruses 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.

5. 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

6. Basic structure of a virus DNA or RNA Capsid protein Naked capsid virus Nucleocapsid + = Lipid membrane, glycoproteins Nucleocapsid Enveloped virus +

7. Relative sizes and detection devices

8. Comparing the size of a virus, a bacterium, and a eukaryotic cell • Viral Size • Millions can fit on pinhead • Smaller than a ribosome!

9. Bacteriophages: Viruses that attack bacteria Basic structure of viruses

10. SHAPES OF VIRUSES • Come in a variety of shapes • Polyhedral • Helical • Complex

11. Viral structure TMV Adenovirus Influenza virus Bacteriophage T4

12. NAKED AND ENVELOPED VIRUSES Matrix Lipid Glycoprotein Icosahedral Helical Naked capsid Enveloped

13. 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

14. General characteristics of viruses Summary • Smallest 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 themselves • Cause many fatal diseases in plants and animals

15. 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)

16. 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.

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