1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 11 The Control of Gene Expression

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings To Clone or Not to Clone? A clone is an individual created by asexual reproduction and thus is genetically identical to a single parent – Cloning an animal using a transplanted nucleus shows that an adult somatic cell contains a complete genome Cloning has potential benefits but evokes many concerns – Does not increase genetic diversity – May produce less healthy animals

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings GENE REGULATION 11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes Gene regulation is the "turning on" and "turning off" of genes – Helps organisms respond to environmental changes Gene expression is the process by which information flows from genes to protein Early understanding of gene control came from studies of the bacterium Escherichia coli

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An operon is a cluster of genes with related functions, along with two control sequences – Promoter: A sequence of genes where the RNA polymerase attaches and initiates transcription – Operator: A sequence of genes between the operon and the promoter that acts as a switch for the binding of RNA polymerase A repressor binds to the operator, stopping transcription A regulatory gene, located outside the operon, codes for the repressor

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The lac operon contains the genes that code for the enzymes that metabolize lactose – Repressor is active when alone and inactive when bound to lactose The trp operon allows bacteria to stop making tryptophan when it is already present – Repressor is inactive alone; must bind to the amino acid tryptophan to be active A third type of operon uses activators, proteins that turn operons on by binding to DNA

8. LE 11-1b Regulatory gene PromoterOperator Lactose-utilization genes OPERON DNA mRNA Protein Operon turned off (lactose absent) DNA mRNA RNA polymerase bound to promoter Active repressor RNA polymerase cannot attach to promoter Protein Lactose Inactive repressor Enzymes for lactose utilization Operon turned on (lactose inactivates repressor)

9. LE 11-1c DNA Active repressor Inactive repressor lac operon Lactose Inactive repressor Active repressor Tryptophan PromoterOperatorGenes trp operon

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.2 Differentiation yields a variety of cell types, each expressing a different combination of genes Gene regulation is much more complex in eukaryotes than in prokaryotes – In multicellular eukaryotes, cells become specialized as a zygote develops into a mature organism – The particular genes that are active in each type of cell are the source of its particular function

11. LE 11-2 Muscle cellPancreas cellsBlood cells

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.3 Differentiated cells may retain all of their genetic potential Though differentiated cells express only a small percentage of their genes, they retain a complete set of genes – Allows for propagation of crop plants – In animal cells can lead to regeneration

13. LE 11-3 Root of carrot plant Root cells cultured in nutrient medium Cell division in culture PlantletAdult plant Single cell

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.4 DNA packing in eukaryotic chromosomes helps regulate gene expression DNA can fit into a chromosome because of packing – DNA winds around clusters of histone proteins, forming a string of bead-like nucleosomes – The beaded fiber coils, supercoils, and further folds into chromosomes DNA packing prevents gene expression most likely by preventing transcription proteins from contacting the DNA

15. LE 11-4 DNA double helix (2-nm diameter) Histones Linker “Beads on a string” TEM Nucleosome (10-nm diameter) Supercoil (300-nm diameter) Tight helical fiber (30-nm diameter) TEM Metaphase chromosome 700 nm

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: DNA Packing Animation: DNA Packing

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.5 In female mammals, one X chromosome is inactive in each cell An extreme example of DNA packing is X chromosome inactivation in interphase cells of female mammals – In each cell line, the X chromosome from either parent may be inactivated – Leads to a random mosaic of expression of the two X chromosomes – Example: coat color in tortoiseshell cat

18. LE 11-5 Early embryo X chromosomes Cell division and random X chromosome inactivation Two cell populations in adult Inactive X Active XOrange fur Black fur Inactive X Active X Allele for orange fur Allele for black fur

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.6 Complex assemblies of proteins control eukaryotic transcription A variety of regulatory proteins interact with DNA and with each other to turn eukaryotic genes on or off In contrast to bacteria – Each eukaryotic gene has its own promoter and control sequences – Activators are more important than repressors

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Eukaryotic RNA polymerase needs the assistance of transcription factors – The binding of activators to enhancers initiates transcription – Silencers inhibit the start of transcription Coordinated gene expression in eukaryotes seems to depend on the association of specific enhancers with groups of genes Animation: Initiation of Transcription Animation: Initiation of Transcription

21. LE 11-6 Enhancers DNA Transcription factors Activator proteins Other proteins RNA polymerase Promoter Gene Bending of DNA Transcription

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.7 Eukaryotic RNA may be spliced in more than one way After transcription, splicing removes noncoding introns Alternative splicing may generate two or more types of mRNA from the same transcript Animation: RNA Processing Animation: RNA Processing

23. LE 11-7 Exons or RNA splicing mRNA RNA transcript DNA

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.8 Translation and later stages of gene expression are also subject to regulation After eukaryotic mRNA is processed and transported to the cytoplasm, there are additional opportunities for regulation – Breakdown of mRNA: The lifetime of an mRNA molecule helps determine how much protein is made – Initiation of translation: A great many proteins control the start of polypeptide synthesis

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Protein activation: After translation, polypeptides may be cut into smaller, active products – Protein breakdown: Rapid selective breakdown of proteins allows the cell to respond to environmental changes

26. LE 11-8 SH Initial polypeptide (inactive) Folded polypeptide (inactive) Active form of insulin Cleavage Folding of polypeptide and formation of S—S linkages SH HS SH S-S

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: mRNA Degradation Animation: mRNA Degradation Animation: Blocking Translation Animation: Blocking Translation Animation: Protein Processing Animation: Protein Processing Animation: Protein Degradation Animation: Protein Degradation

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.9 Review: Multiple mechanisms regulate gene expression in eukaryotes Cellular differentiation results from selective turning on or off of genes at multiple control points – In nucleus DNA unpacking and other changes Transcription Addition of cap and tail Splicing

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – In cytoplasm Breakdown of mRNA Translation Cleavage/modification/activation Breakdown of protein Each differentiated cell still retains its full genetic potential

30. LE 11-9 N UCLEUS Chromosome Gene RNA transcript mRNA in nucleus DNA unpacking Other changes to DNA Transcription Exon Intron Addition of cap and tail Splicing Cap Gene Tail Flow through nuclear envelope C YTOPLASM mRNA in cytoplasm Polypeptide Translation Breakdown of mRNA Broken- down mRNA Cleavage / modification / activation Breakdown of protein Active protein Broken- down protein

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ANIMAL CLONING 11.10 Nuclear transplantation can be used to clone animals Nuclear transplantation – Nucleus of a somatic cell is transplanted into a surrogate egg stripped of nucleus – Cell divides to the blastocyst stage Reproductive cloning – Blastocycst is implanted into uterus – Live animal is born

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Therapeutic cloning – Embryonic stem cells are harvested from blastocyst – These cells give rise to all the specialized cells of the body

33. LE 11-10 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 (blastocyst) Implant blastocyst in surrogate mother Remove embryonic stem cells from blastocyst and grow in culture Clone of donor is born (reproductive cloning) Induce stem cells to form specialized cells (therapeutic cloning)

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 11.11 Reproductive cloning has valuable applications, but human reproductive cloning raises ethical issues Reproductive cloning of nonhuman mammals is useful in research, agriculture, and medicine There are many obstacles, both practical and ethical, to human cloning – Research continues in the absence of consensus

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 11.12 Therapeutic cloning can produce stem cells with great medical potential In culture, embryonic stem cells – Can give rise to all cell types in the body – Must be obtained from human embryos Adult stem cells – Can give rise to many, but perhaps not all, cell types – Are present in adult tissues and, thus, are less controversial than embryonic cells

37. LE 11-12 Adult stem cells in bone marrow Cultured embryonic stem cells Different culture conditions Blood cells Nerve cells Heart muscle cells Different types of differentiated cells

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE GENETIC CONTROL OF EMBRYONIC DEVELOPMENT 11.13 Cascades of gene expression and cell-to- cell signaling direct the development of an animal Studies of mutant fruit flies led to early understanding of gene expression and embryonic development Before fertilization, communication between the egg and adjacent cells determines body polarity A cascade of gene expression controls development of an animal from a fertilized egg Master control homeotic genes regulate batteries of genes that shape anatomical parts

39. LE 11-13a Eye Antenna Leg Head of a normal fruit fly Head of a developmental mutant

40. LE 11-13b Egg cell within ovarian follicle Follicle cells Egg cell Egg protein signaling follicle cells Gene expression in follicle cells Follicle cell protein signaling egg cell Localization of “head” mRNA “Head” mRNA Fertilization and mitosis Embryo Translation of “head” mRNA Gradient of regulatory protein Gene expression Gradient of certain other proteins Gene expression Body segments 0.1 mm Gene expression 0.5 mm Tail endHead end Adult fly Larva

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Video: C. elegans Crawling Video: C. elegans Crawling Video: C. elegans Embryo Development (time lapse) Video: C. elegans Embryo Development (time lapse) Animation: Development of Head-Tail Axis in Fruit Flies Animation: Development of Head-Tail Axis in Fruit Flies

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.14 Signal transduction pathways convert messages received at the cell surface to responses within the cell Signal transduction pathway – Signaling cell secretes signal molecules – Signal molecules bind to receptors on target cell's plasma membrane – Cascade of events leads to the activation of a specific transcription factor

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Transcription factor triggers transcription of a specific gene – Translation of the mRNA produces a protein

44. LE 11-14-4 Signaling cell Signal molecule Receptor protein Plasma membrane Target cell Nucleus Transcription factor (activated) Relay proteins DNA mRNA Transcription Translation New protein

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Overview of Cell Signaling Animation: Overview of Cell Signaling Animation: Signal Transduction Pathways Animation: Signal Transduction Pathways Animation: Cell Signaling Animation: Cell Signaling

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.15 Key developmental genes are ancient Homeotic genes contain nucleotide sequences called homeoboxes – Regulate gene expression during development Similarity of homeoboxes among organisms suggests a very early evolutionary origin

47. LE 11-15 Fly chromosomeMouse chromosomes Fruit fly embryo (10 hours) Mouse embryo (12 days) Adult fruit fly Adult mouse

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE GENETIC BASIS OF CANCER 11.16 Cancer results from mutations in genes that control cell division An oncogene can cause cancer when present in a single copy in a cell A cell can acquire an oncogene from – A virus – A mutation in a proto-oncogene, a normal gene with the potential to become an oncogene

49. LE 11-16a Multiple copies of the gene Proto-oncogene DNA Mutation within the gene Gene moved to new DNA locus, under new controls Oncogene Hyperactive growth- stimulating protein in normal amount Normal growth- stimulating protein in excess Normal growth- stimulating protein in excess New promoter

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tumor-suppressor genes – Normally code for proteins that inhibit cell division – When inactivated by mutation, can lead to uncontrolled cell division and tumors

51. LE 11-16b Tumor-suppressor gene Mutated tumor-suppressor gene Normal growth- inhibiting protein Defective, nonfunctioning protein Cell division under control Cell division not under control

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.17 Oncogene proteins and faulty tumor- suppressor proteins can interfere with normal signal transduction pathways Stimulatory signal-transduction pathway – Stimulates cell division in response to growth factor – Can be stimulated by oncogene proteins that produce hyperactive relay proteins

53. LE 11-17a Growth factor Target cell Receptor Hyperactive relay protein (product of ras oncogene) issues signals on its own Normal product of ras gene Relay proteins Transcription factor (activated) DNA Nucleus Transcription Translation Protein that stimulates cell division

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inhibitory signal-transduction pathway – Inhibits cell division in response to growth- inhibiting factor – Faulty tumor-suppressor genes may produce proteins that fail to inhibit cell division

55. LE 11-17b Protein that inhibits cell division Translation Transcription Protein absent (cell division not inhibited) Normal product of p53 gene Relay proteins Receptor Growth-inhibiting factor Nonfunctional transcription factor (product of faulty p53 tumor-suppressor gene) cannot trigger transcription Transcription factor (activated)

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11.18 Multiple genetic changes underlie the development of cancer Cancers result from a series of genetic changes in a cell linage – More than one somatic mutation is necessary – Accumulation of mutations over time leads to uncontrolled cell division – Example: Colon cancer develops in a stepwise fashion

57. LE 11-18a Colon wall Cellular changes: DNA changes: Increased cell division Oncogene activated Growth of polyp Tumor-suppressor gene inactivated Growth of malignant tumor (carcinoma) Second tumor- suppressor gene inactivated

58. LE 11-18b Chromosomes1 mutation 2 mutations 3 mutations Normal cell Malignant cell 4 mutations

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings TALKING ABOUT SCIENCE 11.19 Mary-Claire King discusses mutations that cause breast cancer Researchers have gained insight into the genetic basis of breast cancer by studying families with a history of the disease A mutation in the gene BRCA1 can put a woman at high risk for breast cancer Environmental influences also play a role

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 11.20 Avoiding carcinogens can reduce the risk of cancer Carcinogens are agents that induce cancer- causing mutations – UV radiation, X-rays – Mutagenic chemical compounds, particularly tobacco smoke Reducing exposure to carcinogens and making other lifestyle choices can help reduce cancer risk