October 12, 2008

October 12, 2008
Quorum Sensing Labs
1. Quorum sensing is bacterial cellular communication
a. Know they are communicating by dense populations of bacteria expressing different genes than individual bacteria
i. Gene expression: turning on/off particular genes in an organism’s genome (total set of DNA an organism has)
b. Bacteria sense high population density, & change gene expression by continuously secreting an autoinducer (AI)
i. The AI for all gram negative bacteria are the homoserine lactones (HSL); cheap and easy to produce
ii. The quorum sensing bacteria also always have AI receptor on surface of cells
iii. When AI binds to the receptor, this triggers a change in bacteria gene expression
1. Move from high concentration to low concentration
2. Vibro fischeri and the Hawaiian bobtail squid (Eurypnma scolopes)
a. the squid has a “light organ” where the Vibro fischeri (normal flora) live
i. nocturnal and is a predator and prey for bigger things
ii. shadow cast by moonlight
iii. by having the “light organ” the bacteria allow them to turn on/off the gene for the light and the shadow from the moonlight disappears
b. at high population densities, Vibro fischeri make luciferase (a light producing enzyme)
3. Pseudomonas aeruginosa and biofilms (see handout for diagrams)
a. Biofilms are dense layers of proteins, lipids, sugars that form a protective coating around bacteria from immune system, antiseptics
i. Rhamnolipid (lipid and carbohydrate) & Pyocyanin (protein)
ii. Rhamnolipid looks like boogers & Pyocyanin is purple and smells like grapes
b. Pseudomonas aeruginosa only produce biofilms
i. Biofilms only made at high population density- Do this by Quorum sensing
ii. Biofilms increase ability of P. aeruginosa to cause disease
Bacterial Genetics
1. The discovery of DNA and the Griffith experiment
a. Deoxyriboneucleic acid
i. Double stranded molecule
ii. Involves 4 bases (A, T, C, G)
iii. Held together by sugar phosphate backbone
iv. DNA is not harmed by heat like proteins are
v. Bacterial genetics are not different (in basics) from anybody else’s genetics
b. In 1928, there was an observation made about mice which stated: that if you have a certain kind of bacteria that grow in glossy looking colonies (streptococcus pnumoniae) and inject it into the mouse, the mouse will die; however, if you have a mouse with rough looking colonies (streptococcus pnumoniae) then the mouse will live
c. Set up experiment with 4 different treatment groups
i. If you inject with glossy streptococcus pnumoniae the mouse dies
ii. If you inject with rough streptococcus pnumonie the mouse lives
iii. Heat killed glossy streptococcus pnumoniae the mouse lives
iv. Heat killed glossy streptococcus pnumoniae and with live rough streptococcus pnumoniae the mouse died
d. Looking at why organisms have the traits they have & what chemical is responsible for traits being heritable
i. Hypothesis 1: proteins
1. Support for proteins are made of 20 amino acids therefore you can have many variations
e. The moral of the Griffrith experiment is that molecules of inheritance/genetic material/ instructions for critter are NOT destroyed by heat, and thus NOT protein
2. Properties of DNA
a. Supercoiled so we can fit all of it into the cell
i. DNA gyrase & topoisomerase 4 uncoils DNA so it can be copied or transcribed
b. Double-stranded with antiparallel strands
i. The 2 strands are pointed in different directions
1. The carbon on one end is 5 carbon and on the other end it’s the 3 carbon sugar
2. The carbon on one end is 3 carbon and the other end it’s the 5 carbon sugar
ii. Bases are attached to a sugar-phosphate backbone
iii. DNA can only be replicated in one direction (5’->3’)
c. Complementary base-pairing->semiconservative replication
i. Complementary base pairing: each can form hydrogen bonds
1. A & T go together (forms 2 hydrogen bonds)
a. Less stable at higher temperatures
2. C & G go together (forms 3 hydrogen bonds)
a. More stable at higher temperature
ii. Semiconservative replication: per copy, one strand is new the other strand is old
3. Steps of DNA replication
a. oriC site (origin of chromosome replication): Where DNA replication begins on the bacterial chromosome
i. uncoil DNA using enzymes (DNA gyrase)
ii. have to unzip strands of DNA where it’s going to be copied
iii. the oriC site has a lot of A & T and no C & G

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