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Gene Regulation
How does a cell known what gene
to express at a given time?
12-5
By the end of this lesson, you
should be able to:
1)
2)
3)
4)
Describe a gene
Explain how prokaryotes control gene
expression by looking at the lac gene
Explain how eukaryotes control gene
expression
Relate gene expression to development
Entrance Question
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Compare the function of RNA & DNA
RNA Function
DNA Function
Synthesizes (makes)
proteins
Holds all of the cell’s
instructions for making
proteins
Now, think about this….
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Do all of your cells hold the same DNA?
Do they all have the same instructions?
Do they all know how to make every
protein your body needs?
Are they all making every possible protein
that you need all of the time?
How does each cell know what protein to
make and when to make it?
Gene Regulation
Gene Expression – determines whether or
not your cell is transcribbing a particular
gene
SWITCHED ON  Transcribbing the DNA
and making the protein it codes for
SWITCHED OFF  The gene is NOT
transcribbed into RNA; it is “silent”
Prokaryotic Gene Regulation
Escherichia coli - (E. coli), is a bacterium
that is commonly found in the lower
intestine of warm-blooded animals. Most E.
coli strains are harmless, but some can
cause serious food poisoning in humans,
and are occasionally responsible for costly
product recalls. The harmless strains are
part of the normal flora of the gut, and can
benefit their hosts by producing vitamin
K2, or by preventing the establishment of
pathogenic bacteria within the intestine.
Lac gene
Important Vocabulary :
Operon – a group of genes that operate together
Promoter – location on the DNA that is the
binding site of the RNA polymerase
Lac Gene
Important Vocabulary:
Repressor – normally turns off the expression of the lac
gene so RNA polymerase can’t bind to the DNA in the O
region
Lactose – a sugar that, if present binds to the repressor
causing it to move from the gene so RNA polymerase
can bind and the lac gene is expressed
O region = Operator – the region on the DNA that controls gene
expresssion by turning “on” or “off”
Eukaryotic Gene Regulation:
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MUCH MORE COMPLEX!!!!
What were introns and exons?
What else looks different?
Differences:
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Operons are not present
Instead they have:
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TATA box – marks the beginning gene
position for the RNA polymerase
Enhancer sequences – areas on the DNA
before the gene that regulate gene expression
when proteins bind to it
Another View…
Development and genes:

1)
2)
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As you grow from a zygote to your size
today, your cells……
Divide
Differentiate – become specialized and
take on different functions
What controls differentation?

Your hox genes – special genes that control
what parts of the body individual cells and
tissues will develop into
Hox Genes
What would
happen if
the hox
genes were
mutated?
Dr. Herrick’s Case Study:
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In 1904, a student from the West Indies came to the
Chicago physician with a puzzling condition
He feels well most of the time but reports odd
recurring events like….
One day after a short swim he became tired and could
hardly move
He was short of breath and had pain in his joints and
muscles
This lasted a few weeks and required some bed rest
He also had frequent fevers and infections
Dr. Herrick examined him and noticed the whites in
his eyes had a yellowish tint
Dr. Herrick’s Case Study
Cont’d:
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His left abdominal area was tender to the touch
and sore
His family history shows he has two brothers
and three sisters, none with this condition
However, his uncle and grandpa had similar
conditions
His grandma died a young woman
His parents do not have this condition
Your Assignment: Do your medical research
to find out the cause of this student’s situation.
Describe what is happening to him and explain
why.