1. © 2010 Pearson Education, Inc. Lectures by Chris C. Romero, updated by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Chapter 11 How Genes Are Controlled

2. © 2010 Pearson Education, Inc. HOW AND WHY GENES ARE REGULATED Every somatic cell in an organism contains identical genetic instructions. –They all share the same genome. –So what makes them different?

3. © 2010 Pearson Education, Inc. HOW AND WHY GENES ARE REGULATED In cellular differentiation, cells become specialized in –Structure –Function Certain genes are turned on and off in the process of gene regulation.

4. © 2010 Pearson Education, Inc. Patterns of Gene Expression in Differentiated Cells 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. Gene for a glycolysis enzyme Hemoglobin gene Antibody gene Insulin gene White blood cell Pancreas cell Nerve cell Active gene Key Colorized TEM Colorized SEM

5. © 2010 Pearson Education, Inc. Gene Regulation in Bacteria 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?

6. © 2010 Pearson Education, Inc. Gene Regulation in Bacteria 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.

7. © 2010 Pearson Education, Inc. 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 Operon turned on (lactose inactivates repressor) Lactose Protein mRNA Lactose enzymes DNA Protein mRNA DNA Operon turned off (lactose absent) Translation Inactive repressor RNA polymerase bound to promoter Transcription Active repressor RNA polymerase cannot attach to promoter Regulatory gene Promoter Operator Operon Genes for lactose enzymes The lac operon

8. © 2010 Pearson Education, Inc. Gene Regulation in Eukaryotic Cells 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 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

9. © 2010 Pearson Education, Inc. 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.

10. 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 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 X chromosome inactivation: the tortoiseshell pattern on a cat

11. © 2010 Pearson Education, Inc. 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 The Initiation of Transcription

12. © 2010 Pearson Education, Inc. Unlike prokaryotic genes, transcription in eukaryotes is complex, involving many proteins, called transcription factors, that bind to DNA sequences called enhancers. The Initiation of Transcription Bend in the DNA Enhancers (DNA control sequences) Transcription factor Transcription Promoter Gene RNA polymerase

13. © 2010 Pearson Education, Inc. 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

14. © 2010 Pearson Education, Inc. 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 RNA Processing and Breakdown

15. RNA transcript Exons RNA splicing mRNA DNA or 1 2 3 5 1 2 4 5 1 2 3 4 1 2 3 5 5 4 In alternative RNA splicing, exons may be spliced together in different combinations, producing more than one type of polypeptide from a single gene.

16. 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 bind to complementary sequences on mRNA molecules in the cytoplasm, and some trigger the breakdown of their target mRNA.

17. © 2010 Pearson Education, Inc. Protein Activation and Breakdown Post-translational control mechanisms –Occur after translation –Often involve cutting polypeptides into smaller, active final products The selective breakdown of proteins is another control mechanism operating after translation. Initial polypeptide Cutting Insulin (active hormone)

18. © 2010 Pearson Education, Inc. Cell Signaling 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.

19. 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 A cell-signaling pathway

20. © 2010 Pearson Education, Inc. Master control genes called homeotic genes regulate groups of other genes that determine 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. Homeotic genes Normal fruit fly Mutant fly with extra wings Normal head Mutant fly with extra legs growing from head

21. © 2010 Pearson Education, Inc. Fruit fly chromosome Fruit fly embryo (10 hours) Mouse chromosomes Mouse embryo (12 days) Adult fruit flyAdult mouse Homeotic genes in two different animals

22. © 2010 Pearson Education, Inc. DNA Microarrays: Visualizing Gene Expression 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.

23. 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 Visualizing gene expression using a DNA microarray

24. CLONING PLANTS AND ANIMALS The Genetic Potential of Cells © 2010 Pearson Education, Inc. Adult plant Young plant Cell division in culture Root cells in growth medium Root of carrot plant Single cell 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.

25. © 2010 Pearson Education, Inc. 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 Regeneration –Is the regrowth of lost body parts –Occurs, for example, in the regrowth of the legs of salamanders

26. © 2010 Pearson Education, Inc. Reproductive Cloning of Animals Nuclear transplantation –Involves replacing nuclei of 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.

27. Donor cell Nucleus from donor cell Remove nucleus from egg cell Add somatic cell from adult donor Grow in culture to produce an early embryo Remove embryonic stem cells from embryo and grow in culture Induce stem cells to form specialized cells for therapeutic use Implant embryo in surrogate mother Clone of donor is born Reproductive cloning Therapeutic cloning Cloning by nuclear transplantation

28. © 2010 Pearson Education, Inc. Other mammals have since been produced using this technique including –Farm animals –Control animals for experiments –Rare animals in danger of extinction Practical Applications of Reproductive Cloning (a) The first cloned cat (right) (c) Clones of endangered animals (b) Cloning for medical use Gray wolf Gaur Banteng Mouflon calf with mother

29. © 2010 Pearson Education, Inc. Therapeutic Cloning and Stem Cells The purpose of therapeutic cloning is not to produce a viable organism but to produce embryonic stem cells. Embryonic stem cells (ES cells) –Are derived from blastocysts –Can give rise to specific types of differentiated cells Adult stem cells –Are cells in adult tissues –Generate replacements for nondividing differentiated cells Umbilical cord blood –Can be collected at birth –Contains partially differentiated stem cells –Has had limited success in the treatment of a few diseases

30. Adult stem cells in bone marrow Cultured embryonic stem cells Different culture conditions Different types of differentiated cells Heart muscle cells Nerve cells Blood cells Differentiation of embryonic stem cells in culture

31. © 2010 Pearson Education, Inc. Oncogenes and Tumor-Suppressor Genes As early as 1911, certain viruses were known to cause cancer. Oncogenes are –Genes that cause cancer –Found in viruses Proto-oncogenes are –Normal genes with the 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.

32. New promoter Normal growth- stimulating protein in excess Normal growth- stimulating protein in excess Hyperactive growth- stimulating protein Gene moved to new DNA position, under new controls Multiple copies of the gene DNA Mutation within the gene Proto-oncogene (for protein that stimulates cell division) Oncogene How a proto-oncogene can become an oncogene

33. © 2010 Pearson Education, Inc. Tumor-suppressor genes –Inhibit cell division –Prevent uncontrolled cell growth –May be mutated and contribute to cancer Defective, nonfunctioning protein Cell division under control (b) Uncontrolled cell growth (cancer) Normal growth- inhibiting protein Cell division not under control (a) Normal cell growth Tumor-suppressor gene Mutated tumor-suppressor gene

34. © 2010 Pearson Education, Inc. The Progression of a Cancer 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 Second tumor-suppressor gene inactivated Tumor-suppressor gene inactivated Oncogene activated DNA changes: Cellular changes: Increased cell division Growth of benign tumor Growth of malignant tumor Colon wall

35. © 2010 Pearson Education, Inc. 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 1 mutation Normal cell Malignant cell 4 mutations 3 mutations 2 mutations Chromosomes

36. © 2010 Pearson Education, Inc. “Inherited” Cancer 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 passed 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

37. © 2010 Pearson Education, Inc. Cancer Risk and Prevention Cancer –Is one of the leading causes of death in the United States –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.

38. Table 11.2

39. Regulatory gene A typical operon Promoter Operator Gene 3 Gene 2 Gene 1 Switches operon on or off RNA polymerase binding site Produces repressor that in active form attaches to operator DNA Summary: gene regulation in bacteria

40. Protein breakdown Protein activation mRNA breakdown RNA transport Translation Transcription DNA unpacking RNA processing Summary: gene regulation in eukaryotic cells

41. Proto-oncogene (normal) Oncogene Mutation Normal protein Mutant protein Defective protein Mutation Normal regulation of cell cycle Normal growth-inhibiting protein Out-of-control growth (leading to cancer) Mutated tumor-suppressor gene Tumor-suppressor gene (normal) Summary: genes that cause cancer

42. © 2010 Pearson Education, Inc. Concept Check  Which of the following cells would likely express the genes that code for glycolysis enzymes? muscle cell white blood cell pancreas beta cells all of these cells none of these cells A. muscle cellB. white blood cellC. pancreas beta cells (and alpha)

43. © 2010 Pearson Education, Inc. Concept Check  Which of the following cells would likely express the genes that code for the hormone insulin? muscle cell white blood cell pancreas beta cells all of these cells none of these cells A. muscle cellB. white blood cellC. pancreas beta cells (and alpha)

44. © 2010 Pearson Education, Inc. Concept Check  Which of the following cells would likely express the genes that code for the hormone gastrin? muscle cell white blood cell pancreas beta cells all of these cells none of these cells A. muscle cellB. white blood cellC. pancreas beta cells (and alpha)

45. © 2010 Pearson Education, Inc. Concept Check  Nuclear transplantation experiments provide strong evidence for which of the following? Differentiated vertebrate cells still maintain their full complement of DNA. Differentiated vertebrate cells do not maintain their full complement of DNA. Vertebrate cloning is not feasible. Cell differentiation is an irreversible process.

46. © 2010 Pearson Education, Inc. Concept Check  Which of the following development events triggers the definition of the head and tail regions in a fruit fly? activation of the homeotic genes in the developing embryo accumulation of “head” mRNA in one end of the unfertilized egg gravitational response in the developing embryo