© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
1
Gene Expression
Every cell has the same genes 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 this
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
2
Organization of DNA
ProkaryotesSeveral million base pairs - one chromosomeRelated genes groupedDNA is mostly coding DNA
EukaryotesBillions of base pairs – several chromosomesGenes not grouped togetherDNA is mostly non-coding DNA
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
3
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
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
4
DNA Packaging
Eukaryotic chromosomes are very large Must be packaged
Unavailable for transcription Unpacking must occur before transcription
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
5
Levels of DNAPackaging Fully condensed,
seen at metaphase Tightly packed loops 30 nm fibers Histone spool Double helix
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
6
Patterns of Gene Expression
Bacteria directly exposed to environment Respond to changes in nutrient availability
Make enzymes for nutrients when they are present
Turn genes off when they are not
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
7
Patterns of Gene Expression
Eukaryotic cells Tissue specific
expression Housekeeping
genes
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
8
Gene Expression: Development
Embryo development depends on gene expression
Timing of expression is complex, yet vital Controlled by cascades of gene
expression
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
9
Master switches Start gene cascades Coordinate development of specific
structures Cell and timing specific expression
Homeotic genes
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
10
Homeotic genes
Similar effects in different organisms
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
11
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
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
12
Control of Gene Expression
E. coli Tryptophan
genes Repressor Operator
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
13
Eukaryotic Gene Expression
More complex than prokaryotic Many different types of regulatory proteins Many DNA elements controlling each gene
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
14
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
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
15
Levels of Gene Control1. Packaging
2. Transcription
3. mRNA breakdown
4. Translation
5. Protein Regulation
6. Protein Degradation
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
16
Gene Control and Phenotype
Can have powerful effectsHomeotic genes
Can result from environmental conditionsGenes turn on and off Phenotype changes
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
17
Process Animation 14.2The Tryptophan Operon
MacintoshWindows
Top Related