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Brandl Lecture 2

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Western University
Biochemistry 2280A
Eric Ball

Biochem - Lecture 2 - Nov. 10th • The first step in a biological process is often highly regulated as it saves energy required in the subsequent steps. Transcription: • because transcription is the first step in gene sequencing, it is often the most reg- ulated • many diseases result from defects in transcription factors (cancer) • the specificity of many transcription factors makes then logical drug targets. Procaryotic Transcription: • mechanistically it is very similar to eucaryotic transcription but it is somewhat sim- pler Terminology: • Operon: a set of genes transcribed from a single promotor and thus expressed from common RNA (coordinately regulated) • Promotor: the DNA sequence required to specifically initiate transcription of a gene (or operon) • Terminator: the DNA sequence required to stop transcription Bacterial Operon Structure: • dsDNA • transcription start site - called +1; base to the left of it is -1 • 3 protein encoding genes downstream from -1 • upstream - promotor sequence required to make RNA • downstream - terminator sequences required to stop DNA The Bacterial Promotor: • a 5’ side • 2 key regulatory sequences elements in a typical bacterial promotor • -10 series and -35 series • -10 is centered about 10bp from the start site of transcription (apprx.) • -35 is about 17bp from -10 Consensus Sequences: • the -10 and -35 sequences are not identical in every promotor • the sequences TTGACA )-35) and TATAAT (-10) are the consensus sequences • consensus sequence: the most frequently occurring base in a group of function- ally relates DNA elements (not always like this, but frequently observed) • doesn’t define what is actually there, just an average Bacterial RNA Polymerase: • the enzyme that makes specific RNA transcripts using DNA as a template and nucleopside triphosphates (NTP’s) as substrates • is a multi subunit enzyme • comes in two forms • core enzyme • holoenzyme Core Enzyme: • the core enzyme will synthesize RNA from ends and nicks in the DNA. • it does not recognize promotors Holoenzyme: • consists of the core enzyme and a sigma subunit • the ability of the RNA polymerase to start transcription only at promoters is con-
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