H OW G ENES ARE C ONTROLLED CM Lamberty General Biology

T OBACCO ’ S S MOKING G UN Southern US major tobacco producer 1950’s: ½ of all Americans smoked 1+ packs/day “health benefits” Rate of lung cancer increased in proportion to tobacco use 1990: lung cancer killing over twice as many men as any other type of cancer 1996: direct link b/t tobacco and cancer BPDE from tobacco smoke binds to DNA w/ gene p53 which codes for protein that normally suppresses tumors

H OW AND W HY G ENES ARE R EGULATED Every somatic cell is produced by repeated rounds of mitosis starting from zygote Each cell has same DNA as zygote Every somatic cell contains every gene. How do cells become different? Contol mechanisms turn on certain genes and turn others off Cellular differentiation Specialized in structure and function Gene regulation The turning on or off of genes

P ATTERNS OF G ENE E XPRESSION In gene expression A gene is turned on and transcribed into RNA Information flows from Genes to proteins Genotype to phenotype Information flows from DNA to RNA to proteins. The great differences among cells in an organism must result from the selective expression of genes.

G ENE R EGULATION IN B ACTERIA Natural selection has favored bacteria that express Only certain genes Only at specific times when the products are needed by the cell So how do bacteria selectively turn their genes on and off? An operon includes A cluster of genes with related functions The control sequences that turn the genes on or off The bacterium E. coli used the lac operon to coordinate the expression of genes that produce enzymes used to break down lactose in the bacterium’s environment. The lac operon uses A promoter, a control sequence where the transcription enzyme initiates transcription An operator, a DNA segment that acts as a switch that is turned on or off A repressor, which binds to the operator and physically blocks the attachment of RNA polymerase

G ENE R EGULATION IN E UKARYOTIC C ELLS Eukaryotic cells have more complex gene regulating mechanisms with many points where the process can be regulated, as illustrated by this analogy to a water supply system with many control valves along the way.

DNA Unpacking of DNA Chromosome Gene Figure

DNA Transcription of gene Unpacking of DNA Chromosome Gene RNA transcript IntronExon Figure

DNA Flow of mRNA through nuclear envelope Processing of RNA Transcription of gene Unpacking of DNA Chromosome Gene RNA transcript IntronExon mRNA in nucleus Tail Cap mRNA in cytoplasm Nucleus Cytoplasm Figure

DNA Flow of mRNA through nuclear envelope Processing of RNA Transcription of gene Unpacking of DNA Chromosome Gene RNA transcript IntronExon mRNA in nucleus Tail Cap mRNA in cytoplasm Nucleus Cytoplasm Breakdown of mRNA Figure

DNA Flow of mRNA through nuclear envelope Processing of RNA Transcription of gene Unpacking of DNA Chromosome Gene RNA transcript IntronExon mRNA in nucleus Tail Cap mRNA in cytoplasm Nucleus Cytoplasm Breakdown of mRNA Translation of mRNA Polypeptide Figure

DNA Flow of mRNA through nuclear envelope Processing of RNA Transcription of gene Unpacking of DNA Chromosome Gene RNA transcript IntronExon mRNA in nucleus Tail Cap mRNA in cytoplasm Nucleus Cytoplasm Breakdown of mRNA Translation of mRNA Various changes to polypeptide Active protein Polypeptide Figure

DNA Flow of mRNA through nuclear envelope Processing of RNA Transcription of gene Unpacking of DNA Chromosome Gene RNA transcript IntronExon mRNA in nucleus Tail Cap mRNA in cytoplasm Nucleus Cytoplasm Breakdown of mRNA Translation of mRNA Breakdown of protein Various changes to polypeptide Active protein Polypeptide Figure

G ENE R EGULATION IN E UKARYOTIC C ELLS The Regulation of DNA packing Cells may use DNA packing for long-term inactivation of genes X chromosome inactivation Occurs in female mammals Is when one of the two X chromosomes in each cell is inactivated at random All of the descendants will have the same X chromosome turned off. If a female cat is heterozygous for a gene on the X chromosome About half her cells will express one allele The others will express the alternate allele

Cell division and X chromosome inactivation Allele for orange fur Early embryo: X chromosomes Allele for black fur Inactive X Active X Inactive X Active X Orange fur Two cell populations in adult cat: Black fur Figure 11.4

G ENE R EGULATION IN E UKARYOTIC C ELLS The Initiation of Transcription The initiation of transcription is the most important stage for regulating gene expression. In prokaryotes and eukaryotes, regulatory proteins Bind to DNA Turn the transcription of genes on and off Unlike prokaryotic genes, transcription in eukaryotes is complex, involving many proteins, called transcription factors, that bind to DNA sequences called enhancers. Repressor proteins called silencers Bind to DNA Inhibit the start of transcription Activators are More typically used by eukaryotes Turn genes on by binding to DNA

Bend in the DNA Enhancers (DNA control sequences) Transcription factor Transcription Promoter Gene RNA polymerase Figure 11.5

G ENE R EGULATION IN E UKARYOTIC C ELLS RNA Processing and Breakdown The eukaryotic cell Localizes transcription in the nucleus Processes RNA in the nucleus RNA processing includes the Addition of a cap and tail to the RNA Removal of any introns Splicing together of the remaining exons In alternative RNA splicing, exons may be spliced together in different combinations, producing more than one type of polypeptide from a single gene. Eukaryotic mRNAs Can last for hours to weeks to months Are all eventually broken down and their parts recycled Small single-stranded RNA molecules, called microRNAs (miRNAs), bind to complementary sequences on mRNA molecules in the cytoplasm, and some trigger the breakdown of their target mRNA.

Exons DNA Figure

RNA transcript Exons DNA Figure

RNA transcript Exons RNA splicing mRNA DNA or Figure

G ENE R EGULATION IN E UKARYOTIC C ELLS The Initiation of Translation The process of translation offers additional opportunities for regulation. Protein Activation and Breakdown Post-translational control mechanism Occur after translation Often involve cutting polypeptides into smaller, active final products The selective breakdown of proteins is another control mechanism operating after translation.

C ELL S IGNALING In a multicellular organism, gene regulation can cross cell boundaries. A cell can produce and secrete chemicals, such as hormones, that affect gene regulation in another cell. Homeotic Genes

SIGNALING CELL Plasma membrane Signal molecule Secretion TARGET CELL Nucleus Figure

SIGNALING CELL Plasma membrane Signal molecule Secretion Receptor protein Reception TARGET CELL Nucleus Figure

SIGNALING CELL Plasma membrane Signal molecule Secretion Receptor protein Reception Signal transduction pathway TARGET CELL Nucleus Figure

SIGNALING CELL Plasma membrane Signal molecule Secretion Receptor protein Transcription factor (activated) Reception Signal transduction pathway TARGET CELL Nucleus Figure

SIGNALING CELL mRNA Plasma membrane Signal molecule Secretion Receptor protein Transcription factor (activated) Reception Signal transduction pathway TARGET CELL Nucleus Transcription Response Figure

SIGNALING CELL mRNA Plasma membrane Signal molecule Secretion Receptor protein Transcription factor (activated) Reception Signal transduction pathway TARGET CELL Nucleus Transcription Response Translation New protein Figure

H OMEOTIC G ENES Master control genes that regulate groups of other genes that determine what body parts will develop in which locations Mutations can produce bizarre effects Similar homeotic genes help direct embryonic development in nearly every eukaryotic organism.

DNA M ICROARRAYS A DNA microarray allows visualization of gene expression. The pattern of glowing spots enables the researcher to determine which genes were being transcribed in the starting cells. Researchers can thus learn which genes are active in different tissues or in tissues from individuals in different states of health.

mRNA isolated Figure

mRNA isolated cDNA made from mRNA Reverse transcriptase and fluorescently labeled DNA nucleotides Fluorescent cDNA Figure

mRNA isolated cDNA made from mRNA cDNA mixture added to wells DNA microarray Reverse transcriptase and fluorescently labeled DNA nucleotides Fluorescent cDNA Figure

mRNA isolated DNA of an expressed gene cDNA made from mRNA cDNA mixture added to wells Unbound cDNA rinsed away Fluorescent spot Fluorescent cDNA DNA of an unexpressed gene DNA microarray (6,400 genes) Nonfluorescent spot DNA microarray Reverse transcriptase and fluorescently labeled DNA nucleotides Fluorescent cDNA Figure

C LONING P LANTS AND A NIMALS The Genetic Potential of Cells Differentiated cells All contain a complete genome Have the potential to express all of an organism’s genes Differentiated plant cells can develop into a whole new organism. The somatic cells of a single plant can be used to produce hundreds of thousands of clones. Plant cloning Demonstrates that cell differentiation in plants does not cause irreversible changes in the DNA Is now used extensively in agriculture

T HE G ENETIC P OTENTIAL OF C ELLS Regeneration Is the regrowth of lost body parts Occurs, for example, in the regrowth of the legs of salamanders

R EPRODUCTIVE C LONING OF A NIMALS Nuclear transplantation Involves replacing nuclei egg cells with nuclei from differentiated cells Has been used to clone a variety of animals In 1997, Scottish researchers produced Dolly, a sheep, by replacing the nucleus of an egg cell with the nucleus of an adult somatic cell in a procedure called reproductive cloning, because it results in the birth of a new animal.

P RACTICAL A PPLICATIONS OF R EPRODUCTIVE CLONING Other mammals have since been produced using this technique including Farm animals Control animals for experiments Rare animals in danger of extinction

H UMAN C LONING Cloning of animals Has heightened speculation about human cloning Is very difficult and inefficient. Critics raise practical and ethical objections to human cloning

T HERAPEUTIC C LONING AND S TEM C ELLS The purpose of therapeutic cloning is not to produce viable organisms but to produce embryonic stem cells Embryonic stem cells (ES cells) Are derived from blastocyst Can give rise to specific types of differentiated cells Adult Stem Cells Are cells in adult tissue Generate replacements for nondividing differentiated cells Embryonic vs. Adult Stem cells Adult cells are partway along the road to differentiation Usually give rise to only a few related types of specialized cells.

U MBILICAL C ORD B LOOD B ANKING Umbilical Cord Blood Can be collected at birth Contains partially differentiated stem cells Has had limited success in the treatment of a few diseases American Association of Pediatrics recommends cord blood banking only for babies born into a family with know genetic risk

T HE G ENETIC B ASIS OF C ANCER In recent years, scientists have learned more about genetics of cancer As early as 1911, certain viruses were known to cause cancer Oncogenes are Genes that cause cancer Found in viruses Proto-oncogenes Normal genes w/ potential to become oncogenes Found in many animals Often genes that code for growth factors, proteins that stimulate cell division For a proto-oncogene to become an oncogene, a mutation must occur in the cell’s DNA

T HE G ENETIC B ASIS OF C ANCER Tumor-suppressor genes Inhibit cell division Prevent uncontrolled cell growth May be mutated and contribute to cancer

T HE P ROGRESSION OF A C ANCER Over 150,000 Americans will be stricken by cancer of the colon or rectum this year Colon cancer Spreads gradually Is produced by more than one mutation

T HE P ROGRESSION OF A C ANCER The development of a malignant tumor is accompanied by a gradual accumulation of mutations that Convert proto-oncogenes to oncogenes Knock out tumor-suppressor genes

“I NHERITED ” C ANCER Most mutations that lead to cancer arise in the organ where the cancer starts In familial or inherited cancer A cancer-causing mutation occurs in a cell that gives rise to gametes The mutation is passes on from generation to generation Breast cancer Is usually not associated with inherited mutations In some families can be caused by inherited, BRCA1 cancer genes

C ANCER R ISK AND P REVENTION Cancer Is one of the leading causes of death in US Can be caused by carcinogens, cancer-causing agents found in the environment, including Tobacco products Alcohol Exposure to ultraviolet light from the sun. Exposure to carcinogens Is often an individual choice Can be avoided Some studies suggest that certain substances in fruits and vegetables may help protect against a variety of cancers

E VOLUTION C ONNECTION : T HE E VOLUTION OF C ANCER IN THE B ODY Evolution drives the growth of a tumor Like individuals in a population of organisms, cancer cells in the body Have the potential to produced more offspring than can be supported by the environment Show individual variation which Affects survival and reproduction Can be passed on to the next generation of cells