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Viruses (19.2 Viruses replicate only in host cells (Viral Genetic material…
Viruses
19.2 Viruses replicate only in host cells
General features of viral replicative cycles
The virus enters the cell and in coated releasing viral DNA & capsid protein
host enzymes replicate the viral genome
host enzymes transcribe the viral genome into viral mRNA
Replicative cycles of phages
some double stranded DNA viruses can replicate by 2 alternative mechanisms, the lytic and lysogenic cycle
The Lytic cycle
a phage replicative cycle that culminates in death of the host cell
virulent phage
a phage that replicates only by a lytic cycle
The Lysogenic cycle
Lysogenic cycle
allows replication of the phage genome without destroying the host
temperate phage
called a Lambda
prophage
the genetic material of a bacteriophage, incorporated into the genome of a bacterium and able to produce phages if specifically activated
Bacterial defense against phages
restriction enzymes
natural selection favors bacterial mutants with surface proteins, then phage DNA does enter a bacterium, the DNA often is identified as foreign and cut by cellular enzymes
CRISPs
clustered regularly interspaced short palindromic
Replicative cycles of animal viruses
Bacteriophage
have an envelope or RNA genome, many animal viruses have both
Viral Genetic material
retroviruses
RNA animal viruses with the most complicated replicative cycle
reverse transcriplase
transcribes an RNA template into DNA, an RNA into DNA
HIV
Human immunodeficiency
AIDS
acquired immunodeficiency lyndrome
Proviruses
integrated viral DNA
viral envelopes
viruses that flare up throughout a person's life
Evolution of viruses
viruses infect every form of life
host range
particular viruses can only effect a limited number of host
19.1 A virus consists of a nucleic acid surrounded by a protien
The discovery of viruses : scientific inquiry
tobacco mosaic diseases experiment
Structure of viruses
infectious particles consisting of nucleic acid enclosed in a protein
viral genomes
single stranded DNA or RNA , double stranded DNA or RNA
Capsids and Envelopes
Capsides
protein shell enclosing the viral genome
viral envelopes
membranous envelope surrounds the capsids of influenza viruse
bacteriophage
complex capsids viruses infect bacteria
phages
capsids infect bacteria
Viruses and prions are formidable pathogens in animals and plants
19.3 Viral diseases in animals
vaccine
is a harmless derivative of a pathogen that stimulates the immune system to mount defense against the harmful pathogen
Emerging viruses
epidemic
widespread outbreak
pandemic
global epidemic