week 4 part 1 lectures.docx
TRANSCRIPT
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Week 4 Lecture 1, Viruses:
What are Viruses? -An infectious particle-Requires a host cell to reproduce-“Obligate Intracellular Parasite”
Viruses are simple and small-The smallest viruses are smaller than ribosomes. -Composed of:
-a genome-a protein shell (capsid)-sometimes a membrane-sometimes carries extra proteins (viral enzymes)
Viral Genomes are Unique-All prokaryotic and eukaryotic genomes are double-stranded DNA.
-Prokaryotic genomes-usually single, circular chromosome. -Eukaryotic genomes-usually multiple, linear chromosomes.
-Viral genomes may consist of single-or double-stranded DNA or RNA.
Viral Capsids-Protein shell encasing genome. -Subunits called capsomeres. -Capsid determines specificity of infection (host range).
-HIV infects humans-SIV infects apes (simians)-FIV infects cats (felines)-West Nile virus infects mosquitoes, birds, and humans
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Generalized Viral Life Cycle-Infection-virus enters host cell -Virus commandeers host machinery and materials to replicate genome and make more viral protein. -New virus assembled and released.
Bacteriophages-Viruses that infect bacteria-Also known as phages-Best understood of all viruses because bacteria are easy to grow-dsDNA (double-stranded DNA) viruses can reproduce using the lytic or the lysogenic life cycle.
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The Lysogenic Cycle-Doesn’t result in death of bacteria. -Virus reproduced with the bacteria because the viral genome inserts into the bacterial genome.
Temperate Phages-Temperate phages use both lytic and lysogenic life cycle to produce virus.
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Animal Viruses with DNA Genome
Animal Viruses with RNA Genomes
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RNA Genomes-Class IV viruses-RNA=mRNA-Class V viruses-RNA is template for mRNA-Class VI viruses (retroviruses)-RNA is template for DNA
Enveloped Viruses-Sometimes animal viruses have a membranous envelope surrounding the capsid. -Contains:
-host-derived phospholipids (host’s plasma membrane)-host-derived transmembrane proteins-viral proteins-viral glycoproteins
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Week 4 Lecture 2, DNA as Genetic Material:
Which macromolecule is the genetic material? Protein with 20 amino acids or DNA with 4 nucleotides? This was the debate for scientists because they had DNA structured in some structure that lacked much diversity.
Transformation discovered by accident-Pneumonia caused by Streptococcus pneumoniaFrederick Griffith hoped to create a vaccine-Studied two strains of the bacteria
Rough bacteria transformed to smooth
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DNA may be the transforming principle-Avery, McCarty, and McLeod found that cell extracts caused transformation-Removed protein, lipid, carbohydrates-Remaining sample caused transformation
Degraded RNA transformation (blue became red circles)Degraded protein transformation (blue became red circles)Degraded DNA no transformation (blue stayed blue circles)
Viruses transfer genetic material to host
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Radioactivity tracks macromolecules
Radioactive viruses function normally
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Blender separates viruses from cells
Viruses insert DNA into cells
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DNA is the genetic material!-Griffith-1928
-Transforming principle converted non-infective rough bacteria into infective smooth bacteria (blue to red circles).
-Avery, MacLeod, McCarty-1944-DNA purified from cell extracts transforms cells. -Destroys DNA prevents transformation.
-Hershey and Chase-1952-Virus transfer DNA to host cells.
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Experimental Basis for DNA Structure