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?
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.
Dec 14, 2015
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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.
11.1 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 proteinCopyright © 2009 Pearson Education, Inc.
Early Research with E. coli:
DNA
RNA polymerasecannot attach to promoter
Lactose-utilization genesPromoter OperatorRegulatorygene
OPERON
mRNA
Activerepressor
Operon turned off (lactose absent)
Protein
DNA
Protein
Inactiverepressor
Lactose Enzymes for lactose utilization
RNA polymerasebound to promoter
Operon turned on (lactose inactivates repressor)
mRNA
DNA
DNA
RNA polymerasecannot attach to promoter
Lactose-utilization genesPromoter OperatorRegulatorygene
OPERON
Protein
mRNA
Inactiverepressor
Lactose Enzymes for lactose utilization
RNA polymerasebound to promoter
Operon turned on (lactose inactivates repressor)
mRNA
Activerepressor
Operon turned off (lactose absent)
Protein
DNA
Inactiverepressor
Activerepressor
Inactiverepressor
Activerepressor
Lactose
Promoter
Tryptophan
Operator Gene
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 transcription2. X-chromosome inactivation in female
mammals- inactivated X called a Barr body3. Individual genes regulated by control
sequences and regulatory proteins
Copyright © 2009 Pearson Education, Inc.
DNA double helix(2-nm diameter)
“Beads ona string”
Linker
Histones
Metaphasechromosome
Tight helical fiber(30-nm diameter)
Nucleosome(10-nm diameter)
Supercoil(300-nm diameter)
700 nm
Two cell populationsin adult
X chromosomes
Early embryo
Allele forblack fur
Inactive X
Black furAllele fororange fur
Orange fur
Cell divisionand random
X chromosomeinactivation 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 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
Otherproteins
DNA
Transcriptionfactors
Activatorproteins
RNA polymerase
Promoter
Gene
Bendingof 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 cellwithin ovarianfollicle
Follicle cells
“Head”mRNA
Proteinsignal
Egg cell
Gene expression1
Cascades ofgene expression2
Embryo Bodysegments
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 (50-250 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
RNAtranscript
mRNA
2 3 4 5
1 2 3 4 5
1 2 4 51 2 3 5
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 spotFluorescent
spot
Actual size(6,400 genes)
Each well contains DNAfrom a particular gene
DNA microarray
mRNAisolated
DNA of anexpressed gene
DNA of anunexpressed gene
Reverse transcriptaseand fluorescent DNAnucleotides
1
cDNA madefrom mRNA
2
cDNA appliedto wells
3
UnboundcDNA rinsedaway
4
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