© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e1 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/e2 Organization of DNA Prokaryotes  Several million base pairs - one chromosome  Related genes grouped  DNA is mostly coding DNA Eukaryotes  Billions of base pairs – several chromosomes  Genes not grouped together  DNA is mostly non-coding DNA

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e3 Genome Size Genome: total component of DNA Prokaryotes  0.6 to 30 million base pairs  Approximately 2,000 genes Eukaryotes  12 million to 1 trillion base pairs  Humans have ~25,000 genes

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e4 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/e5 Levels of DNA Packaging Fully condensed, seen at metaphase Tightly packed loops 30 nm fibers Histone spool Double helix

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e6 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/e7 Patterns of Gene Expression Eukaryotic cells Tissue specific expression Housekeeping genes

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e8 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/e9 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/e10 Homeotic genes Similar effects in different organisms

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e11 Control of Gene Expression Based on two essential elements:  Regulatory DNA: switches gene on/off  Regulatory Protein: binds to regulatory DNA Control gene expression together Respond to environment or cell signals

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e12 Control of Gene Expression E. coli Tryptophan genes Repressor Operator

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e13 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/e14 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/e15 Levels of Gene Control 1. Packaging 2. Transcription 3. mRNA breakdown 4. Translation 5. Protein Regulation 6. Protein Degradation

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e16 Gene Control and Phenotype Can have powerful effects  Homeotic genes Can result from environmental conditions  Genes turn on and off  Phenotype changes

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e17 Process Animation 14.2 The Tryptophan Operon  Macintosh Macintosh  Windows Windows

© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e18 Process Animation 14.3 Control of Gene Expression in Eukaryotes  Macintosh Macintosh  Windows Windows