Download Chapter 12.5

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.