THE CONTROL OF GENE EXPRESSION
THE CONTROL OF GENE EXPRESSION
• GENE EXPRESSION
– THE OVERALL PROCESS BY WHICH GENETIC
INFORMATION FLOWS FROM GENES TO PROTEINS
• PROKARYOTES ARE BEST TO STUDY FOR THIS
TOPIC…WHY??
• THE LAC OPERON IN PROKARYOTES GIVES US
A BETTER UNDERSTANDING OF HOW GENES
ARE EXPRESSED
THE CONTROL OF GENE EXPRESSION
• THE LAC OPERON
THE CONTROL OF GENE EXPRESSION
• THE LAC OPERON
– PRESENT IN E. COLI
– ONLY FUNCTIONAL (TURNED ON) WHEN LACTOSE IS
ABUNDANT…ENVIRONMENTAL CONDITIONS CAN
IMPACT GENE EXPRESSION!!!
– PARTS OF THE OPERON
•
•
•
•
•
OPERON
PROMOTER
OPERATOR
REPRESSOR
REGULATORY GENE
THE CONTROL OF GENE EXPRESSION
• THE LAC OPERON
– HOW DOES IT WORK?!?!
THE CONTROL OF GENE EXPRESSION
• THE LAC OPERON IS NOT THE ONLY OPERON
• OTHER OPERON’S MAY ALSO USE
REPRESSORS; BUT THEY ALSO MAY USE…
– ACTIVATORS  ??
THE CONTROL OF GENE EXPRESSION
• RANDOM QUESTION…YOU STARTED OUT AS A
SINGLE CELL, AND THAT CELL
MULTIPLIED/DIVIDED INTO A TRILLION CELLS
BY THE PROCESS OF MITOSIS; BUT IF MITOSIS
MAKES AN EXACT COPY OF A CELL, HOW
COME EVERY CELL IN YOUR BODY ISN’T
EXACTLY THE SAME???
THE CONTROL OF GENE EXPRESSION
• ANSWER
– EVERY CELL IN YOUR BODY HAS THE EXACT SAME
DNA; HOWEVER, NOT EVERY CELL EXPRESSES THE
SAME DNA!!! (THIS QUESTION IS ON THE REGENTS
EVERY SINGLE YEAR)
• DIFFERENTIATION
– THE PROCESS BY WHICH CELLS BECOME SPECIALIZED
IN STRUCTURE AND FUNCTION
– OCCURS BECAUSE ONLY CERTAIN GENES IN EACH
PARTICULAR CELL ARE TURNED ON, WHILE OTHERS
ARE TURNED OFF (HOW EXACTLY THIS HAPPENS IS
UNKNOWN)
THE CONTROL OF GENE EXPRESSION
• DIFFERENTIATED CELLS RETAIN ALL GENETIC
INFO
– WHEN A CELL DIFFERENTIATES (BECOMES
SPECIALIZED) IT DOESN’T LOSE DNA, JUST
DOESN’T EXPRESS IT
– EVIDENCE OF THIS:
• CLONES
• REGENERATION
• NUCLEAR TRANSPLANTATION
• WHAT EXACTLY ARE STEM CELLS??
THE CONTROL OF GENE EXPRESSION
• ATTEMPTING TO EXPLAIN
THE PROCESS OF
DIFFERENTATION LIES
IN DISCOVERING HOW
EUKARYOTIC CELLS
CONTROL GENE
EXPRESSION
• THIS IS DIFFICULT,
BECAUSE EUKARYOTIC
GENOMES ARE LARGE
AND COMPLEX; BUT WE
SHALL DO OUR BEST!!!
(VICTORY WILL BE OURS!!)
THE CONTROL OF GENE EXPRESSION
• MECHANISMS OF REGULATION IN EUKARYOTIC
GENES
–
–
–
–
–
–
–
–
DNA PACKING
X CHROMOSOME INACTIVATION
COMPLEX PROTEIN ASSEMBLIES
ALTERNATIVE RNA SPLICING
mRNA BREAKDOWN
TRANSLATION INITIATION
PROTEIN INACTIVATION
PROTEIN BREAKDOWN
THE CONTROL OF GENE EXPRESSION
• DNA PACKING
– HISTONES 
– NUCLEOSOME 
– TIGHTLY PACKED DNA
PROBABLY DON’T GET
EXPRESSED
– HISTONES MUST
LOOSEN FOR RNA
POLYMERASE TO BIND
THE CONTROL OF GENE EXPRESSION
• X CHROMOSOME INACTIVATION
– ONE X CHROMOSOME IS TIGHTLY
PACKED/COMPACTED
AND SHUT OFF ENTIRELY
– ONE X CHROMOSOME
IS PICKED AT RANDOM
FOR EACH CELL
– TORTOISE SHELL CAT 
THE CONTROL OF GENE EXPRESSION
• COMPLEX PROTEIN ASSEMBLIES
THE CONTROL OF GENE EXPRESSION
• COMPLEX PROTEIN ASSEMBLIES
– TRANSCRIPTION FACTORS (TF’S) 
– ENHANCERS 
– SILENCERS 
THE CONTROL OF GENE EXPRESSION
• ALTERNATIVE RNA SPLICING
– AN ORGANISM CAN
GET MORE THAN ONE
TYPE OF POLYPEPTIDE
FROM A SINGLE GENE
THE CONTROL OF GENE EXPRESSION
• BREAKDOWN OF mRNA
– mRNA GETS DEGRADED AT DIFFERENT TIMES
• INITATION OF TRANSLATION
– CONTROLLING WHEN TRANSLATION OCCURS
• PROTEIN ACTIVATION
– PROTEIN MAY BE CREATED IN A NON-FUNCTIONAL
STATE
• PROTEIN BREAKDOWN
– PROTEINS GET DEGRADED/BROKEN DOWN AT
DIFFERENT TIMES
THE CONTROL OF GENE EXPRESSION
• MULTIPLE MECHANISM
REGULATE GENE
EXPRESSION
THE CONTROL OF GENE EXPRESSION
• OTHER CONTROL MECHANISMS
– HOMEOTIC GENES
• A MASTER CONTROL GENE THAT REGULATES A BATTERY
(LONG LIST) OF OTHER GENES
– SIGNAL-TRANSDUCTION PATHWAYS
• A SERIES OF MOLECULAR CHANGES THAT CONVERTS A
SIGNAL ON A TARGET CELL’S SURFACE TO A SPECIFIC
RESPONSE WITHIN THE CELL
THE CONTROL OF GENE EXPRESSION
• SIGNAL
TRANSDUCTION
PATHWAYS
– TWO TYPES
THE CONTROL OF GENE EXPRESSION
• CANCER 
– ALL INDIVIDUALS HAVE CANCER GENES WITHIN
THEIR DNA (ONCOGENES)
– THEY ARE NORMALLY CONTROLLED AND KEPT
OFF; HOWEVER, MISTAKES CAN HAPPEN!!!
THE CONTROL OF GENE EXPRESSION
• CANCER
– ONCOGENES
– PROTO-ONCOGENES
– TUMOR-SUPPRESOR GENES
THE CONTROL OF GENE EXPRESSION
• CANCER
– DEVELOPS LATER IN LIFE, MOST OF THE TIME,
BECAUSE IT TAKES AWHILE TO DEVELOP SINCE
MULTIPLE MUTATIONS ARE NECESSARY
THE CONTROL OF GENE EXPRESSION
• CANCER
– EXPOSURE TO CARCINOGENS INCREASES THE RISK
OF DEVELOPING CANCER
– CARCINOGEN  INCREASE THE RATE OF
MUTATION IN CANCER CAUSING GENES, OR
INCREASE THE RATE OF CELL DIVISION
• KNOW EXAMPLES???
• WHAT CAN WE DO TO PREVENT CARCINOGEN
EXPOSURE??
THE CONTROL OF GENE EXPRESSION
• THANKS SO MUCH MR. KRAUZ FOR TEACHING US
ALL THIS COOL INFO ON GENES AND STUFF, BUT
HOW THE HECK DID ANYONE FIND OUT ABOUT
THIS STUFF?
• COME BACK TOMORROW
AND I’LL TELL YOU ABOUT
ALL THE COOL TOYS THAT
SCIENTISTS GET TO PLAY
WITH TO LEARN STUFF
ABOUT GENES!!!