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lect11 - DNA b a s e p a irs Base pairing Anti parallel...

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1 DNA bas e  pairs Base pairing Anti parallel strands
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2 Bas e   pairing DNA sequence (5’ to 3’) Gene sequence Intergenic sequence
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3 DNA Protein Eukaryo tic  Info rm atio n  Trans fe r: Trans c riptio n & Trans latio n ****Beadle and Tatum: Gene = polypeptide****
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4 RNA s e rve s  as  the  inte rm e diary be twe e n DNA and pro te ins Although RNA and DNA are structurally analogous, Three major differences DNA RNA Most DNA is nuclear Most RNA is cytoplasmic Genes are in the nucleus Proteins are made in cytoplasm
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5 Trans c riptio n The synthesis of RNA by the enzyme RNA polymerase using DNA as the template is called transcription For each gene, only one of the two strands of DNA is transcribed mRNA is an exact copy of a gene that is exported to the cytoplasm
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6 Trans c riptio n invo lve s  THREE dis tinc t  pro c e s s e s RNA polymerase catalyzes the synthesis of RNA using the DNA as a template RNA polymerase is a multi-protein complex It consists of four proteins in bacteria (E. coli) 1) Transcription Initiation 2) Transcription Elongation 3) Transcription Termination A GENE is a defined region of DNA It has a start, a body a end.
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7 Initiatio n o f Trans c riptio n Initiation involves RNA polymerase recognizing and binding to a specific sequence on the DNA The recognition sequence is called a PROMOTER The sequences are present in the promoters of most E. coli genes These sequences are conserved They are critical for proper functioning of the promoter ---- TTGACAT --------------- TATAAT ---------- AT ----ATG CCC GGG TTT TAA ---- AACTGTA --------------- ATATTA ---------- TA ---- TAC GGG CCC AAA ATT (-10) (15-17) (-35) PROMOTER 5’ 3’ 3’ 5’ antisense sense What do we mean by conserved sequence? Regions of the DNA (gene or non-gene) or protein that share similar nucleotide sequence
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8 Homology  (molecular biology) Regions of the DNA (gene or non-gene) that share similar nucleotide sequence Sequence homology is a very important concept Structural homology (nucleotide sequence) implies functional homology Conservation of sequence = Conservation of function Genes with a similar sequence are likely to function in a similar manner (Homologous genes encode for similar proteins, which will have similar functions)
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9 Ho m o lo g y is  ne ve r pe rfe c t The sequence homology between genes is not usually perfect Once all the genes are aligned, the most common residue at each position is used to construct a consensus sequence (15-17 bp) Consensus sequences of promoters ---- TTGACAT --------------- TATAAA ---------- AT ----ATG CCC (-10) (-35) (+1) A R T K Q T A R K S T G G K A P R K Q L A T mouse H3 A R T K Q T A R K S T G G K A P R K Q L A T Dros H3 A R T K Q T A R K S T G V K A P R K Q L A T Tetra H3 A R T K Q T A R K S T G G K A P R K Q L A S Yeast H3 A R T K Q T A R K S T G G K A P R K Q L A T Consensus T C C G T T G G A C A T T G T T A G T C G C G - C T T G G T A T A A T C G G C FD8 C G T G T T G A C T A T T T T A C C T C T G G - - C G G T T A T A A T G G T C LPR T C C G C T T G A C A T C C T G A T T G C C G A C T C C C T A T A A A G C G C RRNX1
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