1 gene expression every cell has the same dna yet, each cell is different, specialized differences...
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Gene Expression
Every cell has the same DNA Yet, each cell is different, specialized Differences due to gene expression
Which genes are turned on When the genes are turned on How much product they make
Different factors control all this
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Gene Expression is Influenced by the Organization of DNA Prokaryotes have:
Several million base pairs in one chromosomeRelated genes are grouped togetherDNA that is mostly coding DNA
Eukaryotes have:Billions of base pairs in several chromosomesGenes that are not grouped togetherDNA that is mostly non-coding DNA
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The Organization of DNA is Influenced by the Genome Size Genome: total component of DNA Prokaryotes
0.6 to 30 million base pairsApproximately 2,000 genes
Eukaryotes12 million to 1 trillion base pairsHumans have ~25,000 genes
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Gene Expression is Controlled by DNA Packaging Eukaryotic chromosomes are very large Must be packaged
Unavailable for transcription Unpacking must occur before transcription
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Levels of DNAPackaging Fully condensed DNA,
seen at metaphase Tightly packed loops 30 nm fibers Histone spool Double helix, even this
has to be unpacked for transcription
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Patterns of Gene Expression
Bacteria directly exposed to environment Respond to changes in nutrient availability
Make enzymes for nutrients when they are present (turn on the gene)
Turn genes off when they are not
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Patterns of Gene Expression
Eukaryotic cells Tissue specific
expression Housekeeping
genes
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Gene Expression: Development
Embryo development depends on gene expression
Timing of expression is complex, yet vital Controlled by cascades of gene
expression
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Master switches Start gene cascades Coordinate development of specific
structures Cell and timing specific expression
Homeotic genes
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Homeotic genes
Similar effects in different organisms
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Master Gene Switches: SRY During reproduction, males determine sex
If the sperm has an X, it’s a girl If the sperm has a Y, boy
Y chromosome has the SRY gene SRY is a master switch that controls the
expression of other genes at other loci SRY changes the embryo to develop into
a boy
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Control of Gene Expression
Based on two essential elements:Regulatory DNA: switches gene on/offRegulatory Protein: binds to regulatory DNA
Control gene expression together Respond to environment or cell signals
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Control of Gene Expression
E. coli Tryptophan
genes Repressor Operator
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Eukaryotic Gene Expression
More complex than prokaryotic Many different types of regulatory proteins Many DNA elements controlling each gene In summary, the organization of DNA
controls gene expression in complex ways
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Levels of Gene Control
Tightly packed DNA is not expressed Transcription regulation Regulation of mRNA breakdown Inhibition of translation Regulation of proteins after translation Destruction of completed proteins
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Levels of Gene Control1. Packaging
2. Transcription
3. mRNA breakdown
4. Translation
5. Protein Regulation
6. Protein Degradation
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Gene Control and Phenotype
Can have powerful effectsHomeotic genes
Can result from environmental conditionsGenes turn on and off Phenotype changes
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Process Animation 14.2The Tryptophan Operon
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Process Animation 14.3Control of Gene Expression
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