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Gene regulation
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How does DNA make different cells?
• All cells have a full set of DNA
• Not all the DNA is expressed in each one
• Promoters and repressors allow only certain genes to be expressed (make protein)
Nerve, cardiac, muscle, white blood cells
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The gene that breaks down lactose is repressed
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How it works• When lactose is added, it binds to the
repressor protein.
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Activation
When lactose binds to the repressor, it movesaway, allowing the protein to be made
Left side: why do you think this process is called a “positive” feedback loop?
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Eukaryotic Gene Regulation• Many eukaryotic genes have a sequence
called the TATA box that helps to position
RNA polymerase.
Direction of transcription
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Differentiation• From a fertilized egg to an
adult, cells grow and divide.
• They also differentiate into many different types of cells
• Hox genes control that differentiation
• They are inherited from the genes of our common ancestors
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Gene mutation
• Point mutation: the subtraction, addition or substitution of a single nucleotide
• Changing a nucleotide will change the codon– Can change the amino acid
• Subtraction and addition can cause a “Frame shift” making all amino acids downstream change – This can completely change a protein – Most mutations are harmful
Left side: why don’t all mutations causes changes to the amino acids?
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Not all mutations are equal
• If you put a hox gene for “eye” from a fruit fly into a mouse embryo, it will develop into an mouse eye.
• If you move a hox gene for an eye from the head to the back of a fruit fly embryo the eye will develop on the back
• Small genetic changes can make large changes to an organism.
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Summaryreview
1. What do hox genes do?
2. What are repressors and promoters?
3. What causes a frame shift?