Consider the following…  Do all of the cells in your body carry out the same processes?  Do all of the cells in your body make the same proteins?  Do all of the cells in your body contain the same genes?  What is the connection between genes and protein production?  How is it possible for different types of cells to exist in your body?

 Gene expression is use of genetic info in DNA to make a protein. –Mainly controlled at the level of transcription –A gene that is “turned on” is undergoing transcription and translation; we say it is being expressed –Organisms respond to environmental changes by turning on/off gene expression Copyright © 2009 Pearson Education, Inc Key Point: Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes

 An operon is a group of genes under coordinated control in bacteria  The lactose (lac) operon includes –Three adjacent genes for lactose-utilization enzymes –Promoter sequence where RNA polymerase binds –Operator sequence is where a repressor can bind and block RNA polymerase action –Regulatory gene codes for a repressor protein Copyright © 2009 Pearson Education, Inc. Early Research with E. coli:

DNA RNA polymerase cannot attach to promoter Lactose-utilization genes Promoter Operator Regulatory gene OPERON mRNA Active repressor Operon turned off (lactose absent) Protein

DNA Protein Inactive repressor Lactose Enzymes for lactose utilization RNA polymerase bound to promoter Operon turned on (lactose inactivates repressor) mRNA

DNA RNA polymerase cannot attach to promoter Lactose-utilization genes Promoter Operator Regulatory gene OPERON Protein mRNA Inactive repressor Lactose Enzymes for lactose utilization RNA polymerase bound to promoter Operon turned on (lactose inactivates repressor) mRNA Active repressor Operon turned off (lactose absent) Protein

DNA Inactive repressor Active repressor Inactive repressor Active repressor Lactose Promoter Tryptophan OperatorGene lac operon trp operon

11.2 Key Point: Cell differentiation results from the expression of different combinations of genes  Differentiation involves cell specialization, in both structure and function  Differentiation is controlled by turning specific sets of genes on or off Copyright © 2009 Pearson Education, Inc.

Muscle cell Pancreas cells Blood cells How is gene expression controlled in eukaryotic organisms?

Gene expression in eukaryotes regulated by: 1.DNA packing which prevents transcription 2.X-chromosome inactivation in female mammals- inactivated X called a Barr body 3.Individual genes regulated by control sequences and regulatory proteins Copyright © 2009 Pearson Education, Inc.

DNA double helix (2-nm diameter) “Beads on a string” Linker Histones Metaphase chromosome Tight helical fiber (30-nm diameter) Nucleosome (10-nm diameter) Supercoil (300-nm diameter) 700 nm

Two cell populations in adult X chromosomes Early embryo Allele for black fur Inactive X Black fur Allele for orange fur Orange fur Cell division and random X chromosome inactivation Active X Inactive X Active X

Protein complexes form to regulate transcription  Eukaryotic genes –Each has its own promoter and terminator –Usually switched off and require activators to be turned on –Are controlled by interactions between numerous regulatory proteins and control sequences Gene Switches Gene Switches NOVA 5-min segment from Ghost in Your Genes Copyright © 2009 Pearson Education, Inc.

11.5 Key Point: Complex assemblies of proteins control eukaryotic transcription  Regulatory proteins that bind to control sequences –Transcription factors promote RNA polymerase binding to the promoter –Activator proteins bind to DNA enhancers and interact with other transcription factors –Silencers are repressors that inhibit transcription  Control sequences –Promoter –Enhancer (like operator in prok.) Copyright © 2009 Pearson Education, Inc.

Enhancers Other proteins DNA Transcription factors Activator proteins RNA polymerase Promoter Gene Bending of DNA Transcription

11.10 Key Point: Cascades of gene expression direct the development of an animal  Role of gene expression and embryonic development studied in fruit fly  Master control genes that regulate the genes that actually control the anatomy of body parts  Discovered by studying bizarre fruit fly mutations  Mutation in a single gene led to legs growing out of head in place of antennae Copyright © 2009 Pearson Education, Inc.

Egg cell within ovarian follicle Follicle cells “Head” mRNA Protein signal Egg cell Gene expression 1 Cascades of gene expression 2 Embryo Body segments Adult fly Gene expression 3 4

Head of a normal fruit fly Antenna Eye Head of a developmental mutant Leg

11.6 Eukaryotic RNA may be spliced in more than one way  Alternative RNA splicing –Creates different mRNAs from the same transcript –Results in production of more than one polypeptide from the same gene –Can involve removal of an exon with the introns on either side –Addition of cap (single G nucleotide) and tail ( A nucleotides) facilitate export of mRNA out of nucleus –RNA processing itself is thought to control flow of information out of nucleus since mRNA cannot leave till splicing is complete Copyright © 2009 Pearson Education, Inc. Animation: RNA Processing

1 or Exons DNA RNA splicing RNA transcript mRNA

Key Point: DNA microarrays can be used to determine the expression levels of genes.  DNA microarray (DNA chip or gene chip) –Array has single-stranded DNA molecules that correspond to a single gene; array can have few to 1000s of genes on it –Used to test for transcription –mRNA from a specific cell type is isolated –Fluorescent cDNA is produced from the mRNA –cDNA is applied to the microarray –Unbound cDNA is washed off –Complementary cDNA is detected by fluorescence Copyright © 2009 Pearson Education, Inc.

cDNA Nonfluorescent spot Fluorescent spot Actual size (6,400 genes) Each well contains DNA from a particular gene DNA microarray mRNA isolated DNA of an expressed gene DNA of an unexpressed gene Reverse transcriptase and fluorescent DNA nucleotides 1 cDNA made from mRNA 2 cDNA applied to wells 3 Unbound cDNA rinsed away 4