Presentation on theme: "How Genes Are Controlled"— Presentation transcript:
1 How Genes Are Controlled Chapter 11Aultman Winter 2015
2 Definitions In gene expression, a gene is turned on and transcribed into RNA andinformation flows from genes to proteins andgenotype to phenotype.Information flows from DNA to RNA to proteins.Regulation of gene expression is used to control which genes are expressed, when and how that expression can be modulated.
3 Gene Regulation in Bacteria Natural selection has favored bacteria that expressonly certain genesonly at specific times when the products are needed by the cell.An operon includesa cluster of genes with related functions andthe control sequences that turn the genes on or off.The lac operon usescoordinates the expression of genes that produce enzymes used to break down lactose in the bacterium’s environment.a promoter, a control sequence where the transcription enzyme attaches and initiates transcription,an operator, a DNA segment that acts as a switch that is turned on or off, anda repressor, which binds to the operator and physically blocks the attachment of RNA polymerase and transcription.
4 Eukaryotic Organisms Exhibit a cell cycle. Multicellular Organisms Different genes are expressed during different phasesMulticellular OrganismsEvery somatic cell in an organism contains identical genetic instructions.In cellular differentiation, cells become specialized in structure and function by expressing different genes.Have multiple mechanisms for regulation
5 Regulation of DNA Packing X-chromosome inactivationtakes place early in embryonic development,occurs in female mammals, andone of the two X chromosomes in each cell is inactivated at random.all of the descendants of each cell will have the same X chromosome turned off.If a female is heterozygous for a gene on the X chromosome about half her cells will express one allele and the others will express the alternate allele.
7 Initiation of Transcription Most important stage for regulating gene expression.In prokaryotes and eukaryotes, regulatory proteins bind to DNA and turn the transcription of genes on and off.Unlike prokaryotes,complex, involving many proteins, called transcription factors, that bind to DNA sequences called enhancers.Repressor proteins called silencers bind to DNA and inhibit the start of transcription.Activators are more typically used by eukaryotes than silencers and turn genes on by binding to DNA.
8 RNA Processing and Breakdown transcription localized in the nucleus andRNA processed in the nucleus.RNA processing includes theaddition of a cap and tail to the RNA,removal of any introns,splicing together of the remaining exons.In the cytoplasmmRNAs are translatedMicroRNAs (miRNAs),Small single-stranded RNA moleculesbind to complementary sequences on mRNA molecules in the cytoplasm.Some trigger the breakdown of their target mRNA, and others block translation
9 Alternative RNA Splicing exons may be spliced together in different combinations, producing more than one type of polypeptide from a single gene.A typical human gene contains about ten exons, withnearly all human genes spliced in at least two different ways andsome spliced hundreds of different waysEukaryotic mRNAscan last for hours to weeks to months andare all eventually broken down and their parts recycled.
10 Additional Gene Regulation Mechanisms Transcript or messenger sequestration in the nucleusProteins bind to and protect RNA from degradation, prevent translationInitiation of Translation by ribosomesPost-translational controlProtein Activation or BreakdownMay involve cutting polypeptides into smaller, active final products
11 Cell Signaling gene regulation can cross cell boundaries A cell can produce and secrete chemicals, such as hormones, that affect gene regulation in another cell.
12 Homeotic genes Master control genes called that regulate groups of other genesdetermine what body parts will develop in which locations.Mutations in homeotic genes can produce bizarre effects.Similar homeotic genes help direct embryonic development in nearly every eukaryotic organism examined so far.Ontogeny recapitulates phylogeny
14 The Genetic Potential of Cells Stem cells are undifferentiatedHave the capacity to specialize into many different cell typesEmbryonic stem cells (ES cells)Derived from blastocystsAdult stem cellsPartially differentiatedMay be limited in the number of cell types they can produceUmbilical cord bloodcan be collected at birth,contains partially differentiated stem cells, andhas had limited success in the treatment of a few diseases
15 CloningDifferentiated cells all contain a complete genome and have the theoretical potential to express all of an organism’s genes.Differentiated plant cells can be used to create whole new plantsDifferentiation in plants is reversibleRegeneration of lost or damaged body partsSalamander legsHuman liversReproductive cloning of animalsNuclear transplantationTherapeutic cloning – one child from three parents?
16 Biology and Society: Tobacco’s Smoking Gun Observation: During the 1900s, doctors noticed that smoking increased and lung cancer increasedExperimental setup: lung cells growing in the lab, exposed to various stimuli. Changes in morphology and growth rate were noted.Results: a component of tobacco smoke, BPDE, binds to DNA within a gene called p53, which codes for a protein that normally helps suppress the formation of tumors.Interpretation?
17 Cancer Genetics Certain viruses are known to cause cancer Oncogenes viral genes responsible for cancer formationProto-oncogenes arenormal genes with the potential to become oncogenes,found in many animals, andoften genes that code for growth factors, proteins that stimulate cell divisionA cell can acquire an oncogenefrom a virus orfrom the mutation of one of its own proto-oncogenes
18 Tumor-suppressor genes inhibit cell division,prevent uncontrolled cell growth, andmay be mutated and contribute to cancer.Researchers have identified many mutations in both tumor- suppressor and growth factor genes that are associated with cancer.
19 The Progression of a Cancer Nearly 150,000 Americans will be stricken by cancer of the colon (the main part of the large intestine) this year.Colon cancer, like many cancers,spreads gradually andis produced by more than one mutation.The development of a malignant tumor is accompanied by a gradual accumulation of mutationsconvert proto-oncogenes to oncogenes andknock out tumor-suppressor genes.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 andthe mutation is passed on from generation to generation.
20 Discussion Questions 1Describe the evidence that suggests that cigarette smoking causes lung cancer.Explain how the many types of adult human cells are formed.Explain how the lac operon works.Explain how DNA packing influences gene expression.Why are calico cats always female?Explain how transcription is regulated in eukaryotes. Compare transcriptional regulation in eukaryotes and prokaryotes.
21 Discussion Questions 2Explain how RNA is processed in eukaryotes before it leaves the nucleus. Explain how this processing can result in different proteins from the same gene.Describe the mechanisms used to regulate gene expression after eukaryotic mRNA is transported to the cytoplasm.Describe the significance of cell signaling in multicellular organisms.Explain how homeotic genes help us understand animal evolution and development.Explain how DNA microarrays help scientists visualize gene expression.
22 Discussion Questions 3Explain how every cell has the potential to act like every other cell. Illustrate with examples.Explain how plants are cloned, what this reveals about cell differentiation, and why growers clone plants.Explain how nuclear transplantation can be used to clone animals. Describe advantages of reproductive cloning of animals.Compare the properties of embryonic and adult stem cells. Explain why embryonic stem cells may be better to produce replacement tissues in adults.Explain how mutations in proto-oncogenes and tumor suppressor genes can lead to cancer.Explain how personal habits and individual choices can affect a person’s risk of developing cancers.Explain how populations of cancer cells evolve.