Lecture Notes 11-6

November 4, 2009

Microbiology

DNA and RNA

DNA (instructions: blue print) → RNA (instructions)(provides the template for manufacturing the actual proteins that organisms are made out of → Protein (building blocks of organism)

- Gene ~ DNA instructions that code for a particular protein
o Like a cookbook
o Some genes are expressed in some situations and not in others – like an ‘on/off’ switch
o Ex. Higher population densities turn on the biofilm instruction in pseudomonas aeruginosa
• High level of signaling molecules leads to the expression of a gene

I. Transcription: DNA → RNA
a. Initiation
i. Determining which DNA bits will be copied to RNA
ii. Promoter sequence on DNA
1. Where transcription initiation occurs: where DNA is unwound and unzipped so RNA copy can be made
2. Expect to find a lot of A’s and T’s at the site of the promoter sequence – easier to unzip and unwind
a. TATA box – TATAAT-like sequence at almost all promoter sites/regions
3. While they have common TATA-box sequence, they also vary in their sequence of surrounding bases
iii. RNA polymerase: sigma factors
1. RNA polymerase: copied DNA into RNA copies (RNA copy is single-stranded, complementary to one DNA strand)
a. Where it starts copying is going to determine which genes are transcribed - and where it starts to copy is determined by where the polymerase attached to the DNA to begin unzipping
i. Promoter sequence is where RNA attaches to DNA to begin copying – attaches to DNA’s promoter sequence with one of the sub sequences – sigma factor
2. Sigma Factor: subunit of RNA polymerase that binds to DNA promoter sequences for copying to begin
a. Different sigma factors to attach to different promoter sequences
i. Different sigma factors are expressed under different conditions themselves
ii. Ex. Bacteria under low population densities that don’t have signal cell receptors make one set of sigma factors, BUT bacteria under high population densities make different sigma factors

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