1. © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 11 How Genes Are Controlled

2. Figure 11.0_1 Chapter 11: Big Ideas Control of Gene Expression Cloning of Plants and Animals The Genetic Basis of Cancer

3. CONTROL OF GENE EXPRESSION © 2012 Pearson Education, Inc.

4.  Gene regulation is the turning on and off of genes.  Gene expression is the overall process of information flow from genes to proteins.  The control of gene expression allows cells to produce specific kinds of proteins when and where they are needed.  Our earlier understanding of gene control came from the study of E. coli. 11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes © 2012 Pearson Education, Inc.

5. Figure 11.1A E. coli

6.  A cluster of genes with related functions, along with the control sequences, is called an operon.  With few exceptions, operons only exist in prokaryotes. © 2012 Pearson Education, Inc. Prokaryotes turn genes on or off in response to environmental changes

7. Parts of An Operon  Structural genes: genes under the control of the operon  Promoter: DNA sequence where RNA polymerase binds and initiates transcription of structural genes  Operator: DNA sequence where a repressor can bind and block RNA polymerase action.  Repressor: Protein that binds operator sequence and blacks RNA polymerase  Regulator gene: gene that codes for repressor protein © 2012 Pearson Education, Inc. A typical operon DNA Regulatory gene Promoter Operator Gene 1 Gene 2 Gene 3 Encodes a repressor that in active form attaches to an operator RNA polymerase binding site Switches the operon on or off Code for proteins

8. The lac operon  When an E. coli encounters lactose, all the enzymes needed for its metabolism are made at once using the lactose operon or lac Operon –In the absence of lactose, the repressor binds to the operator and prevents RNA polymerase action. –In presence of lactose, lactose inactivates the repressor –the operator is unblocked –RNA polymerase can bind to the promoter, and –all three genes of the operon are transcribed. © 2012 Pearson Education, Inc.

9. The lac Operon of E. coli Animation: lac operon

10. Figure 11.1B Operon turned off (lactose is absent): OPERON Regulatory gene Promoter Operator Lactose-utilization genes RNA polymerase cannot attach to the promoter Active repressor Protein mRNA DNA Protein mRNA DNA Operon turned on (lactose inactivates the repressor): RNA polymerase is bound to the promoter Lactose Inactive repressor Translation Enzymes for lactose utilization

11. The lac Operon

13. The trp operon  Allows bacteria to produce tryptophan in the absence of this amino acid in environment.  Absence of Tryptophan ACTIVATES trp operon. © 2012 Pearson Education, Inc. Animation: trp operon

14. The trp Operon:

16. Prokaryotic operons  There are two types of repressor-controlled operons. –In the lac operon, the repressor is –active when alone and –inactive when bound to lactose. –In the trp bacterial operon, the repressor is –inactive when alone and –active when bound to amino acid tryptophan (Trp). © 2012 Pearson Education, Inc.

17. Figure 11.1C Inactive repressor Active repressor Lactose Tryptophan DNA Promoter Operator Gene lac operon trp operon

18. 11.2 Chromosome structure and chemical modifications can affect gene expression  Differentiation = cell specialization, in structure and function, and –is controlled by turning specific sets of genes on or off.  Almost all of the cells in an organism contain an identical genome.  The differences between cell types are –not due to the presence of different genes –due to selective gene expression. © 2012 Pearson Education, Inc.differentiation Animation: Differentiation

19. DNA Packaging and Modification  Eukaryotic chromosomes undergo multiple levels of folding and coiling –Nucleosomes are formed when DNA is wrapped around histone proteins. –Each nucleosome bead includes DNA plus eight histones. DNA double helix (2-nm diameter) “Beads on a string” Linker Histones Supercoil (300-nm diameter) Nucleosome (10-nm diameter) Tight helical fiber (30-nm diameter) Metaphase chromosome 700 nm

20. DNA Packaging and chemical modifications can affect gene expression  DNA packing can prevent gene expression by preventing RNA polymerase from contacting the DNA.  More tightly compacted DNA - less likely DNA will be transcribed  Euchromatin - transcriptional active regions of DNA  Heterochromation - transcriptional silent (highly compacted) © 2012 Pearson Education, Inc. Animation: DNA Packing

21. DNA Packaging and chemical modifications can affect gene expression  Methylation of DNA –Certain enzymes can add a methyl group to DNA bases, without changing the sequence of the bases. –Methylation generally inhibits gene expression –Example: X-Chromosome inactivation –Removal of the extra methyl groups can turn on some of these genes. –Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence is called epigenetic inheritance. © 2012 Pearson Education, Inc.

22. DNA packaging and chemical modifications can affect gene expression  X-chromosome inactivation –In female mammals, one of the two X chromosomes is highly compacted and transcriptionally inactive. –An inactivated X chromosome is called a Barr body. –Tortoiseshell fur coloration is due to inactivation of X chromosomes in heterozygous female cats. © 2012 Pearson Education, Inc.

23. Figure 11.2B Cell division and random X chromosome inactivation Early Embryo Adult X chromo- somes Allele for orange fur Allele for black fur Two cell populations Active X Inactive X Active X Inactive X Black fur Orange fur

24. Regulation of Transcription  Eukaryotic RNA polymerase requires the assistance of proteins called transcription factors.  Transcription factors recruit RNA polymerase to gene’s promoter  Activator proteins, which bind to DNA sequences called enhancers and help increase rate of gene transcription.  Silencers are repressor proteins that –may bind to DNA sequences and –inhibit transcription. © 2012 Pearson Education, Inc. Animation: Initiation of Transcription

25. Figure 11.3 Enhancers DNA Promoter Gene Transcription factors Activator proteins Other proteins RNA polymerase Bending of DNA Transcription

26. Regulation of mRNA Processing  Alternative RNA splicing –produces different mRNAs from the same transcript, –results in the production of more than one polypeptide from the same gene © 2012 Pearson Education, Inc. Animation: RNA Processing DNA RNA transcript mRNA Exons Introns Cap Tail RNA splicing or 1 1 1 1 2 2 22 4 4 4 5 5 55 3 3 3

27. 11.5 Small RNAs play multiple roles in controlling gene expression  Only about 1.5% of the human genome codes for proteins.  Another small fraction of DNA consists of genes for ribosomal RNA and transfer RNA.  A flood of recent data suggests that a significant amount of the remaining genome is transcribed into functioning but non-protein-coding RNAs, including a variety of small RNAs. © 2012 Pearson Education, Inc.

28.  microRNAs (miRNAs) can bind to complementary sequences on mRNA molecules either –degrading the target mRNA or –blocking its translation.  RNA interference (RNAi) is the use of miRNA to artificially control gene expression by injecting miRNAs into a cell to turn off a specific gene sequence. © 2012 Pearson Education, Inc. Animation: RNAi 11.5 Small RNAs play multiple roles in controlling gene expression

29. 11.6 Later stages of gene expression are also subject to regulation  After mRNA is fully processed and transported to the cytoplasm, gene expression can still be regulated by –breakdown of mRNA, –initiation of translation, –protein activation, and –protein breakdown. © 2012 Pearson Education, Inc. Animation: mRNA Degradation Animation: Blocking Translation Animation: Protein Processing Animation: Protein Degradation

30. Figure 11.7 The gene expression “pipeline” in a eukaryotic cell Chromosome DNA unpacking Other changes to the DNA Gene DNA Transcription Gene Exon Intron Tail Cap Addition of a cap and tail RNA transcript Splicing mRNA in nucleus NUCLEUS Flow through nuclear envelope mRNA in cytoplasm CYTOPLASM Breakdown of mRNA Translation Polypeptide Broken- down mRNA Cleavage, modification, activation Active protein Amino acids Breakdown of protein

31. 11.7 Review: Multiple mechanisms regulate gene expression in eukaryotes  These controls points include: 1. chromosome changes and DNA unpacking, 2. control of transcription, 3. control of RNA processing including the –addition of a cap and tail and –splicing, 4. flow through the nuclear envelope, 6. breakdown of mRNA, control of translation, and 7. control after translation including –cleavage/modification/activation of proteins and –breakdown of protein. © 2012 Pearson Education, Inc.

32. CLONING OF PLANTS AND ANIMALS © 2012 Pearson Education, Inc.

33. 11.12 Plant cloning shows that differentiated cells may retain all of their genetic potential –Most differentiated cells retain a full set of genes, even though only a subset may be expressed. –Evidence is available from –plant cloning, in which a root cell can divide to form an adult plant and –salamander limb regeneration, in which the cells in the leg stump dedifferentiate, divide, and then redifferentiate, giving rise to a new leg. © 2012 Pearson Education, Inc.

34. Figure 11.12 Root of carrot plant Root cells cultured in growth medium Cell division in culture Single cell Plantlet Adult plant

35. 11.13 Nuclear transplantation can be used to clone animals Animal cloning can use  nuclear transplantation = nucleus of an egg cell replaced with a nucleus from an adult somatic cell.  http://learn.genetics.utah.edu/content/tech/clonin g/clickandclone/ http://learn.genetics.utah.edu/content/tech/clonin g/clickandclone/  Reproductive cloning = nuclear transplantation was first used in mammals in 1997 to produce the sheep Dolly.  http://nortonbooks.com/college/biology/animation s/ch15p02b.htm http://nortonbooks.com/college/biology/animation s/ch15p02b.htm © 2012 Pearson Education, Inc.

36. 11.13 Nuclear transplantation can be used to clone animals  Embryonic stem (ES) cells harvested from a blastocyst used to produce –cell cultures for research or –stem cells for therapeutic treatments. © 2012 Pearson Education, Inc. Animation: Differentiation

37. Figure 11.13_1 The nucleus is removed from an egg cell. Donor cell A somatic cell from an adult donor is added. Nucleus from the donor cell Blastocyst The cell grows in culture to produce an early embryo (blastocyst).

38. Figure 11.13_2 Reproductive cloning Blastocyst The blastocyst is implanted in a surrogate mother. A clone of the donor is born. Therapeutic cloning Embryonic stem cells are removed from the blastocyst and grown in culture. The stem cells are induced to form specialized cells.

39. 11.15 CONNECTION: Therapeutic cloning can produce stem cells with great medical potential  Stem cells grown in laboratory culture –divide indefinitely and –give rise to many types of differentiated cells.  Adult stem cells can give rise to many, but not all, types of cells. © 2012 Pearson Education, Inc.

40. Figure 11.15 Blood cells Nerve cells Heart muscle cells Different types of differentiated cells Different culture conditions Cultured embryonic stem cells Adult stem cells in bone marrow

41. GENTIC BASIS OF CANCER © 2012 Pearson Education, Inc.

42. 11.18 Cancer results from mutations in genes that control cell division –Mutations in two types of genes can cause cancer –Oncogenes –Proto-oncogenes normally promote cell division –Mutations to oncogenes enhance activity –Tumor-suppressor genes –Normally inhibit cell division –Mutations inactivate the genes and allow uncontrolled division to occur Copyright © 2009 Pearson Education, Inc.

43. 11.18 Cancer results from mutations in genes that control cell division –Oncogenes –Promote cancer when present in a single copy –Converting a proto-oncogene to an oncogene can occur by –Mutation causing increased protein activity –Increased number of gene copies causing more protein to be produced –Change in location putting the gene under control of new promoter for increased transcription –Tumor-suppressor genes –Promote cancer when both copies are mutated Copyright © 2009 Pearson Education, Inc.

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

45. 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 Figure 11.18

46. 11.19 Multiple genetic changes underlie the development of cancer –Four or more somatic mutations are usually required to produce a cancer cell –One possible scenario for colorectal cancer includes –Activation of an oncogene increases cell division –Inactivation of tumor suppressor gene causes formation of a benign tumor –Additional mutations lead to a malignant tumor Copyright © 2009 Pearson Education, Inc.

47. 1 Colon wall Cellular changes: DNA changes: Oncogene activated Increased cell division Tumor-suppressor gene inactivated Growth of polyp Second tumor- suppressor gene inactivated Growth of malignant tumor (carcinoma) 2 3

48. Chromosomes 1 mutation Normal cell 4 mutations 3 mutations 2 mutations Malignant cell

49. 11.20 Faulty proteins can interfere with normal signal transduction pathways –Path producing a product that stimulates cell division –Product of ras proto-oncogene relays a signal when growth hormone binds to receptor –Product of ras oncogene relays the signal in the absence of hormone binding, leading to uncontrolled growth Copyright © 2009 Pearson Education, Inc.

50. 11.20 Faulty proteins can interfere with normal signal transduction pathways –Path producing a product that inhibits cell division –Product of p53 tumor-suppressor gene is a transcription factor –p53 transcription factor normally activates genes for factors that stop cell division –In the absence of functional p53, cell division continues because the inhibitory protein is not produced Copyright © 2009 Pearson Education, Inc.

51. Growth factor Protein that Stimulates cell division Translation Nucleus DNA Target cell Normal product of ras gene Receptor Relay proteins Transcription factor (activated) Hyperactive relay protein (product of ras oncogene) issues signals on its own Transcription

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