AN INTRODUCTION TOTHE 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 CYCLE1. Attachment2. 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