BMSC 210 Last 3 Lectures before Midterm 2

• -RNA interference, CRISPR
• -restriction modification system

• -only works against double stranded DNA viruses 
• -RE's cleave DNA 
• -modification of host DNA protects its own DNA

• -chemical modification of viral DNA (glycosylation or methylation)
• -proteins that inhibit RE system

-bacteriophages

• -sum total of all viral genes in an environment
• -most yet to be discovered

• -7 classes of viruses 
• -1975 nobel prize

-single stranded RNA genome with SAME orientation as its mRNA

-single stranded RNA genome with orientation COMPLEMENTARY to its mRNA

-RNA

• -enveloped
• -polymorphic virus
• -segmented genome (8 segments)

• -found as spikes on influenza virus
• -cause clumping of RBC

• -antigenic shift
• -antigenic drift

• -portions of RNA from two distinct strains infect the same cell and are reassorted 
• -generates virions with unique surface proteins
• -produces pandemics

-structures of neuraminidase and hemagglutinin proteins are subtly altered

• -animal viruses that cause certain cancers and immunodeficiency syndrome (AIDS)
• -class VI viruses
• -require reverse transcriptase

• -class VII virus (ds DNA)
• -replicates through RNA intermediate
• -has reverse transcriptase

• -diverse
• -best studied infect enteric bacteria
• -most have dsDNA genomes
• -most naked, some lipid envelopes
• -complex structures

• -virulent mode
• -temperate mode

-viruses lyse host cells after infection

• -viruses replicate their genomes in tandem with host genome without killing host
• -virus can also be lytic

• -linear dsDNA genome
• -infects E. coli
• -virulent life cycle
• -DNA contains 5-hydroxymethylcytosine (resistant to all known RE)

-enzymes needed for DNA replication and transcription

-head and tail proteins and enzymes required to liberate mature phage particles

-can undergo stable genetic relationship within the host

-state where most virus genes are not expressed and virus genome is replicated in synchrony with host chromosome

-bacterium containing a prophage

• -linear dsDNA genome
• -complementary single stranded regions 12 nucleotides long at the 5' terminus of each strand 
• -upon cell penetration DNA ends base pair, creating COS site, where DNA ligates and forms double stranded circle

• -entire virion enters cell (unlike prokaryotes)
• -contain all known modes of viral genome replication
• -many can be enveloped (as virus leaves host cell it steals part of host cell lipid bilayer)

• -RNA viruses that replicate through DNA intermediate
• -enveloped
• -contain reverse transcriptase, integrase and protease 
• -contain specific tRNA

• -unique
• -two identical ssRNA molecules in + orientation
• -contains specific genes gag, pol, env

-encodes structural proteins in retroviral genome

-encodes reverse transcriptase and integrase in retroviral genome

-encodes envelope proteins in retroviral genome

-require other virus (helper virus) to provide some function

-defective viruses for which no intact version exists, rely on unrelated viruses as helpers

• -infectious RNA that lack protein coat
• -smallest known pathogens
• -cause important plant diseases
• -small circular ssRNA genomes
• -do not encode any proteins

• -infectious proteins whose extracellular form contains no nucleic acids
• -misfolding results in neurological symptoms

-pathogenic form transmitted between animals or humans

-random misfolding of a normal healthy prion protein in uninfected individual

-mutation in prion gene yields misfolded protein more often

-4.5 billion years

• -microbial mats with layers of filamentous prokaryotes
• -3.5 billion years old
• -used to be anoygenix filamentous, now oxygenic cyanobacteria

• -formed in inorganic compounds in ponds on surface
• -temp changes, meteor impacts, dust clouds and storms argue against it

• -started in thermal springs on ocean floor
• -more stable conditions
• -H2 and H2S for energy supply

• anoxic
• anaerobic
• chemolithotropic

-4 billion years ago

-laminated sedimentary rocks, prominent features in geological record

-2 billion years old

-transformation of bacteria with DNA extracted from a bacterial virus

-cells capable of taking up DNA and being transformed

-method where electricity is used to force cells to take up DNA (competency)

-transfer of DNA from one cell to another by a bacteriophage

• -general is any portion of host genome packaged into virion
• -specialized specific region of host chromosome is integrated in virus genome