AN INTRODUCTION TO THE VIRUS

LIVING OR NON-LIVING NO, because…  Acellular  Lack both DNA & RNA  Not reproduce on own Must be inside host cell  Not make/store cellular energy (ATP)  Not grow Can mutate

VIRAL STRUCTURES Genome – Single or double strand either DNA or RNA Capsid – Protein coat surrounds genome – Gives shape Envelope – Outer protective coat – Helps hide

VIRAL STRUCTURE Classified according to shape of capsid – Polyhedral: triangular faces – Helical: coiled spring – Complex: bacteriophage

VIRAL REPRODUCTION LYTIC CYCLE 1.Attachment 2.Entry – either entire virus or genetic material injected 3.Replication – viral DNA takes control host cell 4.Assembly – cell used make new viruses 5.Release – cell breaks open LYSOGENIC CYCLE Attachment Entry – Formation of Prophage Joining of host & viral DNA Replication – new gene replicated every time cell goes through mitosis Result: – Become permanent part DNA – External trigger cause virus activate

VIRAL CLASSIFICATION Virulent – Deadly – Evade host’s defenses – Rabies, flu – lytic Temperate – Not cause immediate disease or death – Remain dormant – Lysogenic – HIV, HPV Provirus – Remain dormant in host & reoccur multiple times – Herpes Retrovirus – Contains RNA – Works backwards – RNA  DNA – HIV

VIRAL DISCOVERY Research on Tobacco Plant Diseases Mayer – Show contagious (spread thru plant juices) – Proposed caused small bacteria Ivanowsky – Thru use filtration techniques on sap – proved disease caused something smaller than bacteria Beijerinck – Shows pathogen only reproduce w/in plant (not grow in culture) – Unable to be killed by ethanol – Rejected bacteria theory & came up with the term “virus”

VIRAL DISCOVERY Stanley – First see & crystallize virus known as Tobacco Mosaic Virus – Due to electron microscopy technology