Lecture Notes - Chapter 6 of Microbiology: An Evolving Science
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Course
General Microbiology (BIOM122)
Institution
University Of California - Irvine
Typed lecture notes covering chapter 6 of Microbiology: An Evolving Science, the textbook used in the "General Microbiology" course (BioM122) at UCI. Aligns with lecture 16.
ACTIVE LEARNING (11/16/2020)
• Small, acellular entities. Typically infect specific host and many cells within that • 16SrRNA cannot be used for shotgun sequencing in viruses bc they do not have their own
ribosomes.
host.
○ Can be divided into SYMMETRICAL vs ASYMMETRICAL • Ex. Influenza. Neg sense RNA virus-- opp complimentary.
• Neg strand viruses: single-stranded RNA that are complimentary to the mRNA they
• Virion: virus particle that consist of DNA or RNA in a protein coat->capsid. Aka produce.
nucleic acid surrounded by protein. • Host cell ribosome will read the mRNA synthesized from the virus genome to make viral
• Tropism: virus' ability to infect a particular tissue type. proteins.
6.1: Viruses in Ecosystems • Several strains of a virus can infect an animal.
• Once inside a host cell, it direct host to produce progeny particles by high-jacking • Drift-- modifies structure already there. Ex. Series of point mutations allowing virus to
it's machinery. infect different animal.
• Shift in a viral genome-- new acquisition/segments coming from a viral origin.
• Bacteriophages/phage: viruses that infect bacteria. Replication is observed as
• HIV: Positive-sense, retrovirus.
plaque of lysed cells on a lawn of bacteria, growing in a petri dish. ○ Reverse transcriptase: has a "sloppy genome" that has a high mutation rate -> hard
• The plaque assay: mix bacteria+top agar w/ phage sample. Allow them to grow to develop a vaccine.
on petri dish; clearance zones represent phage has been incorporated into the
bacteria.
• Prophage: bacteriophage that integrates it's genome into host genome.
• Provirus: an integrated viral genome within a human cell.
• Endogenous virus: a permanently integrated provirus transmitted from one
human to another via the germ line.
• Virome: all viral populations in an ecosystem.
• Viruses play a critical role in carbon balance: in marine ecosystems, viruses lyse
cells which unleash nutrients. Viruses kill their aquatic host; dead organic matter
provides carbon/nitrogen for swimmers and bottom dwellers.
• Acute viruses: rapidly kill their hosts; limit host pop density.
○ Surviving hosts have undergone selection for resistance.
○ INC host diversity.
6.2: Virus Structure
• Protein capsid packages the viral genome and delivers it into the host cell.
• Prions: infectious proteins found mostly in the brain. They have no nucleic acid
component; have an abnormal structure that alters conformation of other normal
proteins.
○ Cause brain diseases that lead to spongy brain tissue phenotype. -> Fatal
neurodegenerative disorder!
○ Prions are NOT sensitive to UV radiation!
○ Caused by misfolding proteins (PrP^c); causes other healthy proteins to
misfold abnormally when they come in contact.
○ Misfolding occurs spontaneously w/ low incidence, BUT can be acquired by
eating meat contaminated w/ prions. (Spontaneously* vs Genetically vs
Infectious*)
○ Misfolded protein build-up -> rupture cells -> destroy tissue -> cause
disease.
6.3: Viral Genomes and Classification
• Form of the genome has consequences for the mode of infection and course of a
viral disease.
○ Baltimore classification: based on genome composition and means of
mRNA production.
• Group I: Double-stranded DNA viruses
• Group II: Single-stranded DNA viruses
• Group III: Double-stranded RNA viruses
• Group IV: (+) sense single-stranded RNA viruses
• Group V: (–) sense single-stranded RNA viruses
• Group VI: Retroviruses (RNA reverse-transcribing viruses)
• Group VII: Pararetroviruses (DNA reverse-transcribing viruses)
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