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Immagini e concetti della biologia Sylvia S. Mader Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

B3 - Regulation of Gene Activity Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Prokaryotes control gene expression In prokaryotes, some DNA-binding proteins can turn genes on and off. An operon is a cluster of genes under the control of a single signal. It includes: a regulator gene a promoter an operator structural genes Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Prokaryotes control gene expression The lack operon is an inducible operon, when lactose is absent, the operon is turned off; when lactose is present, the operon is active. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Eukaryotes control gene expression Eukaryotic cells are specialized thanks to the activation/deactivation of certain genes. Active genes in different cells Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Totipotent cells Totipotent cells have the ability to give rise to an entire organism. All plant and animal cells are potentially totipotent cells as the nucleus keeps a copy of all the genes needed for a new individual. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Animal cloning Animals can be cloned using a donor diploid nucleus. The aim of a reproductive cloning is to obtain a new organism, genetically identical to the original. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Animal cloning Desire of a therapeutic cloning is to obtain mature cells of various types for medical purposes. Either embryonic stem cells or adult stem cells may be used in therapeutic cloning. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Animal cloning Benefits Reproductive cloning can help save endangered species. Therapeutic cloning can provide valuable medical products and fight cancer. Drawbacks Donor mitochondrial DNA is not transmitted and the clone may undergo premature aging. In clones, mutation rate is higher and anomalies in gene regulation occur. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Eukaryotes gene control In the nucleus DNA and histone proteins are organized into linear units called chromatin. Before cell division chromatin condenses to form chromosomes. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Eukaryotes gene control The genes in highly condensed chromatin (heterochromatin) are not expressed. Euchromatin consists of loosely condense chromatin whose genes are expressed. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Transcription-regulating proteins DNA-binding proteins regulate transcription in eukaryotes. Transcription factors are proteins that help regulate transcription. Transcription activators bind to specific regions of DNA (enhancer) and promote transcription. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

mRNA influences gene expression Post transcriptional gene control occurs in the nucleus. It involves: the primary mRNA splicing; the speed at which mRNA leaves the nucleus. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Cytoplasmic gene expression control The last control of gene expression occurs in the cytoplasm during and after the translation. Translational control begins when processed mRNA reaches the cytoplasm before the protein production. Post-translational control begins once a protein has been synthesized and becomes active. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Gene expression control review Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Gene expression in development In order to have a proper development, genes must be turned on and off in an exact sequence. In Drosophila melanogaster some genes determine the development of both anterior/posterior body axes and body segmentation. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Homeotic genes and apoptosis Homeotic genes determine segmentation and which segment develops what body parts. Homeotic genes contain homeobox, DNA sequence involved in anatomical development. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Genetic mutations and cancer Apoptosis (programmed cell death) is important in cancer control. Proto-oncogenes, promote the cell cycle and inhibit apoptosis. Tumor suppressor genes, protect the cell from the development of the cancer. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Genetic mutations and cancer Oncogenes and mutated tumor suppressor genes cause excess cyclin which stimulates the cell cycle and makes p53 unavailable so that apoptosis does not occur. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Genetic mutations and cancer Products of faulty genes interfere with signal transduction when cancer develops. A stimulatory signal transduction pathway turns on a proto-oncogene whose products stimulates the cell cycle. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Genetic mutations and cancer When cancer occurs the products of an oncogene leads to overstimulation of the pathway and the cell cycle excellerates. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Genetic mutations and cancer An inhibitory signal transduction pathway turns on a tumor suppressor gene whose products inhibits the cell cycle. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Genetic mutations and cancer When cancer occurs, the product of a mutated tumor suppressor gene fails to turn on the pathway and fails to stop the cell cycle. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Cancer development Carcinogenesis is the development of a malignant tumor due to repeated mutations. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Cancer development Angiogenesis (formation of new blood vessels) provides nutrients to a growing tumor. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Cancer development Motile cells invade lymphatic and blood vessels, metastasis occur when new tumors form far from the original site. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Cancer therapy Cancer diagnosis includes a complete check of patient health, imagine diagnostics, blood and urine analysis, endoscopy. Surgery of a cancer cell mass is useful only for solid tumors. Chemotherapy is a cancer treatment that uses drugs to destroy cancer cells. Radiotherapy uses high energy rays to destroy cancer cells. Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012