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

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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings GENE REGULATION 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings GENE REGULATION 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

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)

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings GENE REGULATION 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

LE 11-2 Muscle cellPancreas cellsBlood cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings GENE REGULATION 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings GENE REGULATION 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DNA Splicing 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings DNA Regulation 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 – Initiation of translation – Protein activation – Protein breakdown

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ANIMAL CLONING 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

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

LE 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)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE GENETIC CONTROL OF EMBRYONIC DEVELOPMENT 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Transduction 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings THE GENETIC BASIS OF CANCER 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

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

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