GENE EXPRESSSION. Promoter sequence where RNA polymerase binds. Operator sequence that acts as a switch (yellow) OPERON

Transcription

1 GENE EXPRESSSION 1 GENE REGULATION IN PROKARYOTES Bacteria can turn genes on or off depending on their environment Prokaryotes have operons clusters of related genes and regulatory sequences Promoter sequence where RNA polymerase binds Operator sequence that acts as a switch (yellow) OPERON RNA polymerase is bound to the promoter Translation Enzymes for lactose utilization 2 1

2 INDUCIBLE OPERONS IN PROKARYOTES Always turned off by repressor protein. Regulatory genes are always on and code for a small amount of repressor proteins. Repressors block the operator so transcription can not take place Example: lactose in gut bacteria Operon turned off OPERON Regulatory gene Promoter Operator Lactose-utilization genes mrna RNA polymerase cannot attach to the promoter Protein Active repressor 3 REPRESSIBLE OPERONS (PROKARYOTES) Always turned on. Can be turned off by activator protein Tryptophan (Trp) is made by gut bacteria When Trp is present in the gut (you ate poultry) protein synthesis is switched off and Trp in gut is absorbed instead. lac operon (inducible) Promoter Operator Gene trp operon (repressible) Active repressor Active repressor Tryptophan Inactive repressor Lactose Inactive repressor 4 2

3 GENE REGULATION IN EUKARYOTES Chromosome structure and chemical modifications affect gene regulation in eukaryotes double helix (2-nm diameter) Metaphase chromosome Beads on a string Linker Nucleosome (10-nm diameter) Tight helical fiber (30-nm diameter) Histones Supercoil (300-nm diameter) 700 nm 5 X INACTIVATION Inactivation of genes on one X chromosome in female mammals Early Embryo Adult X chromosomes Cell division and random X chromosome Active X inactivation Inactive X Two cell populations Orange fur Allele for orange fur Allele for black fur Inactive X Active X Black fur 6 3

4 TRANSCRIPTION FACTORS Groups of proteins that affect transcription in eukaryotes Default for most eukaryotic genes is off activator proteins are more important than repressors Transcription factors Enhancers Activator proteins Other proteins Promoter Gene -bending protein RNA polymerase Bending of Transcription 7 RNA & GENE REGULATION ALTERNATIVE SPLICING During splicing, RNA can make make multiple mrna strands from one sequence RNA INTERFERANCE Micro RNA (mirna) can bind to proteins and block translation or cause degradation of mrna to turn a gene off Exons Introns Introns Cap RNA transcript RNA splicing Tail mrna or

5 LATER STAGES OF GENE CONTROL mrna BREAKDOWN mrna is eventually broken down. It can be long or short lived depending on its function. INITITATION OF TRANSLATION Inhibitors can suppress translation of mrna into polypeptides PROTEIN ACTIVATION Polypeptides are usually altered after translation for their specific function. Timing of this process can be controlled PROTEIN BREAKDOWN Proteins are eventually broken down. They can be long or short lived depending on their function. 9 ANIMAL DEVELOPMENT 1. Unfertilized egg communicates with follicle cells surrounding it 2. Genes specify for accumulation of head mrna at one end 3. After fertilization, embryo grows (mitosis). Homeotic genes control other anatomy genes and segments develop 4. Cells become specialized and result in a fully formed fly Egg cell within ovarian follicle Egg cell Egg cell and follicle 1 cells signaling Follicle cells each other Gene expression Growth of egg cell Localization of head mrna 2 Head mrna Embryo 3 Adult fly 4 Egg cell Cascades of gene expression Fertilization and mitosis Body segments Expression of homeotic genes and cascades of gene expression 10 5

6 SIGNAL TRANSDUCTION PATHWAYS A series of molecular changes that convert a signal from one cell into a response from a neighboring cell EXAMPLES: Cell cycle control system How yeast identify mates Signaling cell 1 Relay proteins Transcription factor (activated) 2 Signaling molecule Receptor protein 4 EXTRACELLULAR FLUID 3 Signal transduction pathway Hormones 5 mrna Transcription 6 New protein Translation 11 MOLECULAR GENETICS OF CANCER ONCOGENES genes that can cause cancer when present in a single copy of a cell (caused by mutations or viruses) PROTO ONCOGENES normal genes that have the potential to become oncogenes (by mutations) TUMOR SUPPRESOR GENES Genes that inhibit cell division (can result in cancer if mutated) BRCA1&2 Chromosomes 1 mutation 2 mutations 3 4 mutations mutations Normal cell Malignant cell 12 6

7 LIFESTYLE & CANCER Carcinogens mutagens that alter and cause cancer Include XRAYS, UV sunlight, tobacco, alcohol Diet can decrease risk of cancer 13 CLONING OF PLANTS AND ANIMALS Clone: an individual produced through asexual reproduction of a single parent Nuclear transplantation replacing the nucleus of an egg or zygote with the nucleus of an adult somatic cell Reproductive cloning implanting the egg or zygote in a surrogate mother resulting in live birth of a new living individual Donor cell Nucleus from the donor cell Blastocyst The nucleus A somatic cell The cell grows in The blastocyst is removed from an adult culture to produce is implanted in a from an donor is added. a blastocyst (early surrogate mother. egg cell. embryo). A clone of the donor is born. 14 7

8 CLONING IS CONTROVERSIAL Favored for food, pharmaceuticals and endangered species Short life expectancy and often poor health of clones Clones do not contribute to genetic diversity of populations 15 THERAPEUTIC CLONING OF STEM CELLS EMBRYONIC STEM CELLS are found in a fertilized zygote that has divided into a blastocyst. These cells can differentiate into any type of cell. ADULT STEM CELLS are not abundant in adult bodies. These cells have already differentiated and can only give rise to specific cells that do not reproduce on their own (bone marrow blood cells) Adult cells Blood cells Embryonic stem cells Nerve cells Heart cells 16 8

9 GENE CLONING Using bacterial plasmids to create recombinant Bacteria Cell with desired gene PLASMID small circular that replicate separately from other bacterial chromosomes RECOMBINANT Combined pieces of from two different sources Bacterial plasmid Recombinant Replicated used Proteins produced Recombinant replicated by bacteria 17 GENETICS & MEDICINE Insulin previously obtained by slaughtering pigs and cattle Vaccines can be created by producing molecules on virus surface or by creating mutant viruses that are not harmful 18 9

10 GENETICS & AGRICULTURE Genetically modified organisms (GMOs) have acquired one or more genes by artificial means. They are called transgenic organisms. BENEFITS Longer shelf life Increased yield Pest or disease resistance Nutritional value Cost less to produce Resistant to herbicides CONCERNS Human health? Impact on natural ecosystems Resistant weeds Damage to pollinating insects Increased herbicides in food Recombinant plasmid is inserted into plant cell and incorporated into plant chromosomes Plant cells grown in the lab to create a transgenic plant with desired trait(s) 19 REQUIRED VIDEOS NO VIDEO Study for your exam!!!! 20 10