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Sylvia S. Mader
Immagini e
concetti
della biologia
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
B3 - Regulation
of Gene Activity
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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
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Gene expression control review
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cancer development
Carcinogenesis is the development of a malignant tumor
due to repeated mutations.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012
Cancer development
Angiogenesis (formation of new blood vessels) provides
nutrients to a growing tumor.
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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.
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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.
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Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012