Transcript Regulation & Mutations

10-6
Gene Control
• Prokaryotes turn genes on and off by controlling
transcription
• Promoter
• DNA segment that allows a gene to be transcribed
• Helps RNA polymerase find where the gene starts
• Operator
• DNA segment that turns genes on or off
• Operon
• Region of DNA including the promoter, the
operator, and genes that code for proteins
• Example : lac operon breaks down lactose sugar
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Gene Control
• Eukaryotes regulate genes at many points
• Exons
• Nucleotide segments that code for parts of the
protein
• Introns
• Nucleotide segments that occur between exons
• Removed before mRNA leaves the nucleus
• Role is not clear
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10-7
Mutations
• Change to the DNA code
• 2 types
1. Gene Mutation
• affect a single gene
• Occur during replication
• 2 types
1. Point Mutation
• One nucleotide is substituted by another
• Usually caught by DNA polymerase
• If not caught, it changes the DNA code
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10-7
Mutations
1. Gene Mutation
• 2 types
2. Frameshift Mutation
• Insertion or deletion of a nucleotide
• Shift the entire DNA sequence because mRNA is
read three nucleotides at a time
• Example : ABC DEF GHI JKL…
• With deletion: ABD EFG HIJ KL…
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10-7
Mutations
• 2 types
• Chromosomal Mutation
• Affect an entire chromosome
• Occurs during meiosis
• 2 types
1. Gene duplication
• Homologous chromosomes did not align properly
• Crossing over does not result is equal sizes being
exchanged
• Extra copies of genes on one chromosome and
missing copies of genes on the other
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10-7
Mutations
• 2 types
• Chromosomal Mutation
• 2 types
2. Translocation
• Piece of chromosome moves to non-homologous
chromosome
• Like crossing over but with chromosomes that
are not identical
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10-7
Results of Mutations
• Some cause death or diseases or malfunctions
• Some are not noticed at all
• Some lead to abnormalities that assist the organism
and make them better suited for their environment
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10-7
Causes of Mutations
• Errors during replication
• These are usually fixed by DNA polymerase
• Mutagens
• Agents in the environment that change DNA
• Ex: UV rays and chemicals
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