Download AN INTRODUCTION TO THE VIRUS

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
1.
2.
3.
4.
5.
LYTIC CYCLE
Attachment
Entry – either entire virus
or genetic material
injected
Replication – viral DNA
takes control host cell
Assembly – cell used make
new viruses
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