Chapter 11 The Control of Gene Expression Power

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

• Cloning has many benefits – But evokes just as many concerns 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 • Early understanding of gene control Figure 11. 1 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Colorized SEM 7, 000 – Came from studies of the bacterium Escherichia coli

The lac Operon • In prokaryotes, genes for related enzymes – Are often controlled together in units called operons Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Regulatory proteins bind to control sequences in the DNA – And turn operons on or off in response to environmental changes OPERON Regulatory gene Promoter Operator Lactose-utilization genes DNA m. RNA Protein RNA polymerase cannot attach to promoter Active repressor Operon turned off (lactose absent) RNA polymerase bound to promoter DNA m. RNA Protein Lactose Figure 11. 1 B Inactive repressor Operon turned on (lactose inactivates repressor) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Enzymes for lactose utilization

Other Kinds of Operons • The trp operon – Is similar to the lac operon, but functions somewhat differently Promoter Operator Genes DNA Active repressor Tryptophan Inactive repressor Lactose Figure 11. 1 C lac operon Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings trp operon

11. 2 Differentiation yields a variety of cell types, each expressing a different combination of genes • In multicellular eukaryotes – Cells become specialized as a zygote develops into a mature organism Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Different types of cells – Make different proteins because different combinations of genes are active in each type Figure 11. 2 Muscle cell Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Pancreas cells Blood cells

11. 3 Differentiated cells may retain all of their genetic potential • Most differentiated cells – Retain a complete set of genes Root of carrot plant Single cell Figure 11. 3 Root cells cultured in nutrient medium Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cell division in culture Plantlet Adult Plant

11. 4 DNA packing in eukaryotic chromosomes helps regulate gene expression • A chromosome contains DNA – Wound around clusters of histone proteins, forming a string of beadlike nucleosomes DNA double helix (2 -nm diameter) Histones TEM “Beads on Linker a string” Nucleosome (10 -nm diameter) Tight helical fiber (30 -nm diameter) 700 nm TEM Figure 11. 4 Supercoil (300 -nm diameter) Metaphase chromosome Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• This beaded fiber – Is further wound and folded • DNA packing tends to block gene expression – Presumably by preventing access of transcription proteins to the DNA 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 in interphase cells – Is X chromosome inactivation in the cells of female mammals Two cell populations in adult Early embryo X chromosomes Cell division and random X chromosome inactivation Active X Orange fur Inactive X Figure 11. 5 Allele for orange fur Allele for black fur Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Inactive X Active X Black fur

11. 6 Complex assemblies of proteins control eukaryotic transcription • A variety of regulatory proteins interact with DNA and with each other – To turn the transcription of eukaryotic genes on or off Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Transcription Factors • Transcription factors – Assist in initiating eukaryotic transcription Enhancers Promoter Gene DNA Transcription factors Activator proteins Other proteins RNA polymerase Bending of DNA Figure 11. 6 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transcription

Coordinating Eukaryotic Gene Expression • Coordinated gene expression in eukaryotes – Seems to depend on the association of enhancers with groups of genes Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

11. 7 Eukaryotic RNA may be spliced in more than one way • After transcription, alternative splicing – May generate two or more types of m. RNA from the same transcript Exons DNA RNA transcript or RNA splicing Figure 11. 7 m. RNA 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 m. RNA is fully processed and transported to the cytoplasm – There additional opportunities for regulation Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Breakdown of m. RNA • The lifetime of an m. RNA molecule – Helps determine how much protein is made Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Initiation of Translation • Among the many molecules involved in translation – Are a great many proteins that control the start of polypeptide synthesis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Protein Activation • After translation is complete S SH Cleavage SH S S Initial polypeptide (inactive) Folded polypeptide (inactive) Figure 11. 8 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings S SH SH S Folding of polypeptide and formation of S—S linkages S SH SH – Polypeptides may require alteration to become functional S S S Active form of insulin S

Protein Breakdown • Some of the proteins that trigger metabolic changes in cells – Are broken down within a few minutes or hours Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

11. 9 Review: Multiple mechanisms regulate gene expression in eukaryotes NUCLEUS Chromosome DNA unpacking Other changes to DNA Gene Transcription Exon RNA transcript Intron Addition of cap and tail Tail Splicing m. RNA in nucleus Cap Flow through nuclear envelope m. RNA in cytoplasm CYTOPLASM Breakdown of m. RNA Translation Brokendown m. RNA Polypeptide Cleavage / modification / activation Active protein Breakdown of protein Figure 11. 9 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Brokendown protein

ANIMAL CLONING 11. 10 Nuclear transplantation can be used to clone animals Donor cell Nucleus from donor cell Implant blastocyst in surrogate mother Remove nucleus Add somatic cell from adult donor from egg cell Clone of donor is born (reproductive cloning) Grow in culture to produce an early embryo (blastocyst) Remove embryonic stem Induce stem cells to cells from blastocyst and form specialized cells grow in culture (therapeutic cloning) Figure 11. 10 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 Figure 11. 11 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Critics point out that there are many obstacles – Both practical and ethical, to human cloning Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

CONNECTION 11. 12 Therapeutic cloning can produce stem cells with great medical potential • Like embryonic stem cells, adult stem cells – Can perpetuate themselves in culture and give rise to differentiated cells Blood cells Adult stem cells in bone marrow Nerve cells Cultured embryonic stem cells Figure 11. 12 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Heart muscle cells Different culture conditions Different types of differentiated cells

• Unlike embryonic stem cells – Adult stem cells normally give rise to only a limited range of cell types 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 • Early understanding of the relationship between gene expression and embryonic development – Came from studies of mutants of the fruit fly Drosophila melanogaster Eye SEM 50 Antenna Figure 11. 13 A Head of a normal fruit fly Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Leg Head of a developmental mutant

• A cascade of gene expression – Controls the development of an animal from a fertilized egg Egg cell within ovarian follicle 1 Follicle cells Egg protein signaling follicle cells Gene expression in follicle cells Follicle cell protein signaling egg cell 2 Localization of “head” m. RNA 3 “Head” m. RNA Embryo Fertilization and mitosis Translation of “head” m. RNA Gradient of regulatory protein 4 Gene expression Gradient of certain other proteins 5 Gene expression Body segments 6 0. 1 mm Larva Gene expression Adult fly Figure 11. 13 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Head end 7 Tail end 0. 5 mm

• Homeotic genes – Control batteries of genes that shape anatomical parts such as antennae 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 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Signal transduction pathways – Convert molecular messages to cell responses Signaling cell Signal molecule 1 Receptor protein 2 Plasma membrane 3 Target cell Relay proteins 4 Transcription factor (activated) Nucleus DNA 5 m. RNA Transcription New protein 6 Figure 11. 14 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Translation

11. 15 Key developmental genes are very ancient • Homeotic genes contain nucleotide sequences, called homeoboxes – That are very similar in many kinds of organisms Fly chromosome Fruit fly embryo (10 hours) Figure 11. 15 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Adult fruit fly Mouse chromosomes Mouse embryo (12 days) Adult mouse

THE GENETIC BASIS OF CANCER 11. 15 Cancer results from mutations in genes that control cell division • Cancer cells, which divide uncontrollably – Result from mutations in genes whose protein products affect the cell cycle Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

Proto-Oncogenes • A mutation can change a proto-oncogene (a normal gene that promotes cell division) – Into an oncogene, which causes cells to divide excessively Proto-oncogene DNA Mutation within the gene New promoter Oncogene Hyperactive growthstimulating protein in normal amount Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Gene moved to new DNA locus, under new controls Multiple copies of the gene Normal growthstimulating protein in excess Figure 11. 16 A Normal growthstimulating protein in excess

Tumor-Suppressor Genes • Mutations that inactivate tumor suppressor genes – Have similar effects as oncogenes Tumor-suppressor gene Normal growthinhibiting protein Cell division under control Figure 11. 16 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Mutated tumor-suppressor gene Defective, nonfunctioning protein Cell division not under control

11. 17 Oncogene proteins and faulty tumorsuppressor proteins can interfere with normal signal transduction pathways Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Oncogene proteins – Can stimulate signal transduction pathways Growth factor Receptor Target cell Hyperactive relay protein (product of ras oncogene) issues signals on its own Normal product of ras gene Relay proteins Transcription factor (activated) DNA Nucleus Figure 11. 17 A Protein that stimulates cell division Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transcription Translation

• Tumor-suppressor proteins – Can inhibit signal transduction pathways Growth-inhibiting factor Receptor Relay proteins Transcription factor (activated) Nonfunctional transcription factor (product of faulty p 53 tumor-suppressor gene) cannot trigger transcription Normal product of p 53 gene Transcription Figure 11. 17 B Protein that inhibits cell division Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Translation Protein absent (cell division not inhibited)

11. 18 Multiple genetic changes underlie the development of cancer • Cancers result from a series of genetic changes in a cell lineage Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Colon cancer – Develops in a stepwise fashion Colon wall 1 2 Cellular changes: Increased cell division Growth of polyp Growth of malignant tumor (carcinoma) DNA changes: Oncogene activated Tumor-suppressor gene inactivated Second tumorsuppressor gene inactivated Figure 11. 18 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 3

• Accumulation of mutations – Can lead to cancer Chromosomes Normal cell 1 mutation 2 mutations Figure 11. 18 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 3 mutations 4 mutations Malignant cell

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 in which a diseasepredisposing mutation is inherited Figure 11. 19 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

CONNECTION 11. 20 Avoiding carcinogens can reduce the risk of cancer • Reducing exposure to carcinogens (which induce cancer-causing mutations) – And making other lifestyle choices can help reduce cancer risk Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Cancer in the United States Table 11. 20 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings