Differentiated cells liver cells nerve cells blood

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differentiated cells Liver cells Nerve cells Blood cells Embryonic stem cells Adult stem cells
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DNA OFF OFF OFF mRNA mRNA mRNA mRNA mRNA Another transcription factor MyoD Muscle cell (fully differentiated) MyoD protein (transcription factor) Myoblast (determined) Embryonic precursor cell Myosin, other muscle proteins, and cell-cycle blocking proteins Other muscle-specific genes Master control gene myoD Nucleus Determination. Signals from other cells lead to activation of a master regulatory gene called myoD , and the cell makes MyoD protein, a transcription factor. The cell, now called a myoblast, is irreversibly committed to becoming a skeletal muscle cell. 1 Differentiation. MyoD protein stimulates the myoD gene further, and activates genes encoding other muscle-specific transcription factors, which in turn activate genes for muscle proteins. MyoD also turns on genes that block the cell cycle, thus stopping cell division. The nondividing myoblasts fuse to become mature multinucleate muscle cells, also called muscle fibers. 2 Determination of Cell type
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Cytoplasmic determinants Molecules of another cyto- plasmic deter- minant Figure 21.11a Unfertilized egg cell Molecules of a a cytoplasmic determinant Fertilization Zygote (fertilized egg) Mitotic cell division Two-celled embryo Cytoplasmic determinants in the egg. The unfertilized egg cell has molecules in its cytoplasm, encoded by the mother’s genes, that influence development. Many of these cytoplasmic determinants, like the two shown here, are unevenly distributed in the egg. After fertilization and mitotic division, the cell nuclei of the embryo are exposed to different sets of cytoplasmic determinants and, as a result, express different genes. (a) Nucleus
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Cell differentiation Different cell types result from different gene expression in cells with the same DNA Differences in gene expression Not differences in the cells’ genomes
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Problems Ethical Source of embryonic cells When does life begin?
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Human Genome Project Started in 1990 International effort to identify all human genes and to sequence all the base pairs 20 centers in 18 countries: China, France, Germany, UK, Japan, and the US Competitor was a private company, Celera Genomics April 14, 2003: map of the human genome was completed Consists of 20,000 protein-coding genes Bases identified and placed in their order and potential genes assigned to chromosomes
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Human Genome Project
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Human Genome Project What we have learned from HGP Nearly 50% genes do not yet have a function Summary of findings: The human genome consists of ~3.1 billion base pairs The genome is approximately 99.9% the same between nationalities Less than 2% of the genome codes for genes Most DNA is non-protein coding, with repetitive DNA sequences The genome contains ~ 20,000 protein-coding genes Can make 100,000+ proteins
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Human Genome Project Chromosome 1 contains the highest number of genes.
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