notes 11-6

November 6, 2009
Continuation of Bacterial Genetics
1) Protection of the bacterial chromosome from degradation
a) Methylation: CH3 added to adenine and cytosines on bacteria chromosome as last DNA replication step
• Advantage#1: allows mismatch repair system to identify old vs. new ( example: “right” vs.”wrong”) DNA strands
• Allows identification of potential viral DNA
b) Restriction enzymes: enzymes that recognize/bind to particular sequences of DNA bases in DNA strand and break DNA strand there ( example: 5’ ATCCCGCA3’)
• Bacteria make lots of different restriction enzymes that bind to/ break DNA at lots of different sequences
• Defense against viral infections
• Viral DNA not methylated
Transcription handout
DNA(instructions, like a blueprint)----RNA--——Protein( building blocks of organism) Transcription

Gene: DNA instructions for a particular protein
1) Transcription: DNA—- RNA
a) Initiation: determining which bit of DNA will be copied to RNA
• Promoter sequence: when transcription initiation occurs—where DNA is unwound and unzipped so RNA copy can be made
 Have lots of T&As( TATA box—TATAAT- like sequence at almost all promoter sites)
 While have common TATA-box sequence, also have variability in surrounding bases
• RNA polymerase: enzyme that copies DNA into RNA copy. ( RNA copy is single-stranded, complementary to one DNA strand)
 RNA polymerase binds to promoter sequences on DNA
 Sigma factor: subunit of RNA polymerase that binds to DNA promoter sequences
 Different sigma factors attach to different promoter sequences
 Different sigma factors expressed under different conditions

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