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Control of Eukaryotic Genes AP Biology 2007-2008 The BIG Questions… How are genes turned on & off in eukaryotes? How do cells with the same genes differentiate to perform completely different, specialized functions? AP Biology The BIG Review Carrying information in DNA DNA codes for one amino acid in sets of three (codon) Amino acids link to form polypeptides Genes code for polypeptides that control: The expression of traits (how we look) The function of the cell Other genes AP Biology Epigenetics What causes cells with the same DNA to differentiate? There are chemical reactions which activate and deactivate parts of the genome. Epigenetics is the study of these chemical reactions and the factors that influence them. AP Biology Epigenome A genome is the complete set of DNA. Epi means "above". The epigenome consists of chemical compounds that mark the genome. The marks tell the DNA what to do, where to do it and when to do it. Can be passed on from cell to cell as cells divide, and from one generation to the next. AP Biology Changes to the Epigenome Development (during growth) Environmental chemicals Drugs and medicines Aging Diet AP Biology Gene Expression • Gene – segment of DNA that codes for a specific gene product • Gene product – functional protein or RNA molecule • Gene expression – using the information in a gene to produce a gene product Regulation in Gene Expression • All cells within an organism contain the same DNA sequence • Only a small portion of genes are expressed in a given cell – Expressed continuously – Expressed only when needed – Many genes are never expressed Regulation in Gene Expression • Cells have the ability to regulate: – Timing of gene expression (turn genes on and off) – Amount of gene product produced Process of Gene Expression • Four major stages: – – – – Transcription RNA processing RNA transport Protein translation Gene Primary transcript mRNA • Regulation occurs at all four stages Protein Regulation of Transcription • Transcription – synthesis of an mRNA transcript from a gene Gene Primary transcript • Regulated by: – Structural DNA changes – Transcription factors – Environmental factors Transcription Factors • Transcription factors – proteins that bind to specific DNA sequences to promote or suppress gene expression • Can bind to promoter, and start or stop RNA polymerase from binding. Environmental Factors • Internal factors – Cells release signaling proteins that change gene expression • External factors – Temperature – Oxygen Regulation of RNA Processing • RNA processing – modification of initial mRNA transcript to remove sections not needed. Primary transcript mRNA • Regulated by: – Splicing – removing sections – Binding and degrading mRNA Regulation of RNA Transport • RNA transport – export of mature mRNA from nucleus to cytoplasm in eukaryotes • Regulated by: – Proteins that limit the amount of mRNA exiting the nucleus mRNA Regulation of Protein Translation • Protein translation – synthesis of a protein from mature mRNA transcript • Regulated by: – mRNA structure and proteins that affect translation starting – Environmental factors • Example: temperature Protein Protein Modification • Protein structure can be changed by the chemicals processing them. • Protein folding may be changed and protein will be inactive. Regulation of Gene Expression Learning Objectives • Describe the process of gene expression • Recognize factors that regulate gene expression Gene Primary transcript mRNA Protein Cellular Differentiation Stem Cells | Differentiation Process Cellular Differentiation Learning Objectives • Describe cellular differentiation • Identify the roles of DNA, RNA, and environmental factors in the cellular differentiation process Stem Cells • Stem cell – a biological cell that can divide and differentiate into specialized cell types – Includes both embryonic and adult stem cells • Cellular differentiation – the process of converting a stem cell into a specialized cell Differentiation Process • Differentiation occurs during – Development – Growth – Repair Differentiation Process • Proteins control cell differentiation – Direct structural changes – Direct the cell to begin specialized functions • Differentiation of an individual cell depends on the involvement of DNA, RNA, and the environment Role of DNA • DNA can only be used when it is uncoiled • The segments of DNA that are uncoiled determine how the cell will differentiate Role of RNA • RNA controls differentiation during and after transcription – Removes pieces of mRNA during processing, altering the protein produced – Binds and destroy mRNA strands, stopping protein production Role of Environmental Factors • Environmental factors can trigger the cell to modify gene expression • Internal factors – Specialized cells send out signaling proteins that bind receptors on stem cells • External factors – Temperature – Oxygen Using Stem Cells for Tissue Regeneration • Tissue regeneration research is attempting to alter the differentiation of stem cells – Embryonic stem cells • Only in developing embryos – Adult stem cells • Remain undifferentiated in adults Using Stem Cells for Tissue Regeneration • Scientists attempt to initiate cell differentiation using – Biochemical signaling agents – Varying environmental conditions – Embryonic genes in adult stem cells Cellular Differentiation Learning Objectives • Describe cellular differentiation • Identify the roles of DNA, RNA, and environmental factors in the cellular differentiation process