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Chapter 19: Viruses (Concept 19.2: Viruses replicate in host cells…
Chapter 19: Viruses
Concept 19.2: Viruses replicate in host cells
host range
limited number of host species a virus can infect
general feature of viral replicative cycle
begins when a virus binds to a host cell and the viral genome is inside
next the proteins encoded take control of the host cell, and the cell copies the viral genome and viral proteins
afterwards the components are produced they self-assemble into new viruses
Replicative Cycles of Phages
The Lytic Cycle
phage replication that results in the death of the host cell
virulent phage
phage which only replicates only by a lytic cycle
The Lysogenic Cycle
allows replication of the phage genome without destroying the host
temperate phage
phages capable of using both types of cycles
prophage
when integrated into bacterial chromosome the viral DNA is known as this
Bacterial Defenses Against Phages
restriction enzymes
when phage DNA enters a bacterium but identified it is cut up by cellular enzymes
Replicative Cycles of Animal Viruses
retroviruses
RNA animal viruses with the most complicated replication cycle
reverse transcriptase
enzyme that transcribes RNA into DNA which is opposite of the normal direction
provirus
integrated viral DNA which never leaves the host's genome
Concept 19.1: Virus consist of nucleic acid surrounded by a protein coat
Structure of Viruses
Virus
Infectious particle with genes packaged inside a protein coat
Smallest viruses are 20nm in diameter, and largest is 1,500nm which is barely visible under a light microscope.
Discovery of Viruses
Tobacco mosaic disease was studied in 1883 by Adolf Mayer
Test were run to determine if the disease was a bacteria but was still about to cause problems leading to a possibility of something smaller than bacteria.
Viral Genomes
Virus genomes can consist of four strands
double stranded DNA single stranded DNA double stranded RNA single stranded RNA
Capsids and Envelopes
capsid
protein shell enclosing the viral genomes
viral envelopes
membranous envelope surrounding phospholipids and membrane protein
bacteriophages
complex capsids found among viruses that infect bacteria
Concept 19.3: Viruses and prions
Viral Diseases in Animals
vaccine
harmless derivative of a pathogen that stimulates the immune system
antibiotics only help against bacterial infections but are defenseless against viral infections
Emerging Viruses
epidemic
a widespread outbreak affecting a large area
pandemic
a global outbreak
Three processes of emerging viruses
Second is the emergence of a viral disease from a small population
Third is the spread of viral diseases from other animals
First is the mutation of existing viruses
Viral Diseases in Plants
vertical transmission
viral infection in inherited from a parent
horizontal transmission
plant is infected from an external source of the virus