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CHAPTER 12.5 GENE REGULATION • GENES ARE ABLE TO TURN ON AND OFF. ONLY A FEW GENES ARE EXPRESSED AT ANY TIME. • AN EXPRESSED GENE IS A GENE THIS IS TRANSCRIBED INTO RNA. • IN FRONT OF GENES THERE IS A PROMOTER REGION, BUT THERE ARE ALSO REGULATORY SITES – THESE TURN ON AND OFF THE GENE. GENE REGULATION: AN EXAMPLE • WE WILL USE E. COLI TO GIVE AN EXAMPLE OF TURNING A GENE ON AND OFF. • THE 4288 PROTEIN REGION IS MADE OF 3 GENES. THESE 3 GENES GET TURNED OFF AND ON TOGETHER. THESE GENES ARE RESPONSIBLE FOR BREAKING DOWN LACTOSE FOR THE BACTERIA. • A GROUP OF GENES THAT THAT TURN OFF AND ON IS CALLED AN OPERON. IN E. COLI THIS GROUP OF GENES IS CALLED THE LAC OPERON. • THE E. COLI ONLY NEEDS THESE GENES TURNED ON WHEN IT USES LACTOSE FOR FOOD. IF THERE IS NO LACTOSE IT DOES NOT NEED THESE GENES TURNED ON. • THE LAC GENES ARE TURNED OFF BY REPRESSORS AND TURNED ON BY THE PRESENCE OF LACTOSE. HOW DOES IT WORK? • ON ONE SIDE OF THE OPERON’S GENES ARE 2 REGULATORY PROTEINS. • THE PROMOTER REGION IS WHERE RNA POLYMERASE CAN ATTACH AND START TRANSCRIPTION. • THERE IS ANOTHER REGION CALLED THE OPERATOR. THIS CONTAINS A PROTEINS CALLED A LAC REPRESSOR. IF THE LAC REPRESSOR IS ATTACHED TO THE DNA THE GENE IS TURNED OFF. • THE REPRESSOR WILL BE ON DNA UNLESS LACTOSE IS PRESENT. WHEN LACTOSE IS PRESENT IT CHANGES THE SHAPE OF THE REPRESSOR AND THE REPRESSOR IS REMOVED. EUKARYOTIC GENE REGULATION • THERE ARE DIFFERENCES BETWEEN PROKARYOTES AND EUKARYOTES. • EUKARYOTES USUALLY DO NOT HAVE OPERONS. • MOST EUKARYOTIC GENES ARE CONTROLLED INDIVIDUALLY AND ARE MORE COMPLEX. • USUALLY EUKARYOTIC GENES WILL HAVE A TATA BOX (A SEQUENCE OF TATATA) BEFORE THE GENE. THIS AREA HELPS RNA POLYMERASE BIND TO THE DNA. DEVELOPMENT AND DIFFERENTIATION • REGULATION OF GENE EXPRESSION IS VERY IMPORTANT IN CELL SPECIALIZATION. • WHEN AN ORGANISM IS DEVELOPING IT’S CELLS UNDERGO DIFFERENTIATION – THEY BECOME SPECIALIZED IN STRUCTURE AND FUNCTION. • HOX GENES CONTROL CELL DIFFERENTIATION AND HELP MAKE DIFFERENT BODY PARTS.