101509-BCH311

101509-BCH311 - What is a gene? Denition of a gene from the...

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What is a gene? Definition of a gene from the National Human Genome Research Institute The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein. Definition of a gene from the U.S. Department of Energy Human Genome Project National Human Genome Research Institute The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or RNA molecule). How are genes recognized? How are genes used to direct the synthesis of proteins?
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Table 11-1, p.265 General features of Transcription
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E. coli RNA polymerase Molecular weight ~470 kDa Multisubunit enzyme termed the holoenzyme ( α 2 ωββ σ ) (like the DNA Pol III holoenzyme) σ - subunit is weakly attached and is involved in the recognition of promoter sequences The promoter is the DNA sequence that signals the start of transcription α 2 ωββ is the core enzyme and comprises the active polymerization site The core enzyme is catalytically active but lacks specificity Specificity of the RNA Pol holoenzyme is conferred by the σ - subunit - through the recognition of specific promoter sequences
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Fig. 11-1, p.265 RNA polymerase reads the 3’ to 5’ strand - this strand is known as the template or antisense strand - and synthesizes RNA in the 5’ to 3’ direction The top strand is the coding or sense strand The coding strand has the same sequence as the RNA that is produced ( except U replaces T ) e.g. ATG GCA TGC AAT AUG GCA UGC AAU Overview of Prokaryotic Transcription
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Gene Promoter Structure A specific DNA sequence called the promoter ‘marks’ the start of a gene σ -subunit of RNA polymerase recognizes the promoter sequence (which lies ‘upstream’ of the transcription start site) Four important promoter ‘elements’ 1. +1 transcription start site (1-3 core promoter) 2. -10 region (Pribnow box) 3. -35 region (or -35 element) 4. UP element (-40 to -60) (1-4 extended promoter) *Consensus sequence - a DNA or RNA sequence that is conserved (or very similar), e.g. TATAAT for the Pribnow box Promoter regions are typically AT-rich - 2 x H-bonds per bp - more easily unwound There are strong and weak promoters, depending on how tightly RNA polymerase binds (which in turn is dependent on the DNA sequence) The stronger the promoter, the tighter RNA Pol binds, the greater the frequency of gene transcription, more mRNA, more protein produced
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Gene Promoter Structure The first base to be incorporated into the RNA chain is said to be at position +1 and is called the transcription start site The first promoter element 10 bp upstream is known as the -10 region or Pribnow box After the Pribnow box there are 16-18 bp that are completely variable
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101509-BCH311 - What is a gene? Denition of a gene from the...

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