Lecture Notes Sept 14

We revisit the anthrax letters case, and use that to discuss bacterial genetic structures like their circular chromosomes, and the plasmids that can confer such nifty abilities as surviving antibiotics and making lethal factor. We then chat about ribosomes, and wrap things up with a thought question on why cephalexin made my infected spider bite inflammation worse before it got better.

Bruce Ivans: Sent Anthrax letters in Sept. 2001
-Anthrax is gram positive spore forming bacterium; bacilli shaped
-grow on blood agar
-causes your skin to turn black and fall off
III. Bacterial genetic structures, anthrax, and 9/11
a. Nucleoid (not a nucleus) bunched up bacterial DNA
i. Most bacteria have circular chromosomes
-Have just one bacterium per chromosome
-pairs of chromosomes are X shaped
-An individual human chromosome is linear shaped
-In contrast, eukaryotic chromosomes are almost always linear/chromosomes are in multiple sets; whereas bacteria tend to have only 1 chromosome per bacterium and the chromosomes tend to be circular
-There are 46 chromosomes per cell, which are in 23 pairs

-Because bacteria just have one chromosome bacteria do not have dominantly recessive traits; in a sense all traits are dominant

-One of the reasons why bacteria have circular chromosomes is because this is why bacteria are able to divide indefinitely and not lose any genetic information
-Every time your cells divide they get shorter and shorter which results in death, which is why we die

Bacterial chromosomes are circular
Bacterial cell divide and set of enzymes attach to the DNA and the DNA can’t be copied where the enzymes are bound
So, the bacteria starts copying the dna in a circle which takes a while which results in enzymes falling off and then the DNA is completely copied
Do not lose any genetic information when they divide unlike eukaryotic chromosomes

b. Plasmids
-Little circles of DNA that have Genes on them for extra bonus options
-Only a couple of genes on them
-these genes are often called accessory genes
-accessory genes are something that is nice to have, but isn’t something that is absolutely needed
-For example, Plasmids often have genes for antibiotic resistence on them or in the case of B. anthracis there is a gene for lethal factor and the more copies of the lethal factor gene containing plasmid the worse factors/symptoms in a person infected
-Easy for bacteria to share plasmids with other bacteria

-if we see antibiotic resistance in some bacteria were worried about that trait being spread by other bacteria because as previously described, in many cases the antibiotic resistance gene or genes are on plasmids, plasmids are easily shared among bacteria so even if you had another bacteria that wasn’t exposed to an antibiotic themselves, they could still pick up an antibiotic resistance gene through other antibiotic resistances genes on those other plasmids

Kirby Bower test results on ciprofloxacin and penicillin
Why were people given cipro instead of penicillin? (last class period)
-people were prescribed cipro for 60 days
-later, someone tested that penicillin would be just as good

October 2001: Strains of anthracis that had been genetically engineered to be resistant to penicillin
This done by putting plasmids with penicillin resistant genes into bacteria

(Will look at ii at a later date)

IV. Ribosomes

-synthesize proteins by translating mRNA into an iminoacid sequence

Acid Fast Cell Envelope (Picture)
-inner most layer is the cell membrane
-cell membrane made of phospholipid bilayer
-squiggles-cell wall made of mycolic acid
-has a circular chromosome
-and lots of ribosomes within the plasma membrane

Thought question about bacterial cell envelope (end of class)
Spider bite:
-bacteria infected wound
-symptoms: hot, swollen, painful, inflammation
-Takes antibiotics (betalactam drug that attacks the bacterial cell wall)
-Inflammation got worse than what it was before taken the antibiotics
On Wednesday, What is up with step 4? Why are you getting worse? Are the bacteria gram positive or gram negative?

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