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8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E The student is expected to: 5C describe the roles of DNA, ribonucleic acid (RNA) and environmental factors in cell differentiation; 6C explain the purpose and process of transcription and translation using models of DNA and RNA; 6D recognize that gene expression is a regulated process; 6E identify and illustrate changes in DNA and evaluate the significance of these changes 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E KEY CONCEPT Gene expression is carefully regulated in both prokaryotic and eukaryotic cells. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E Prokaryotic cells turn genes on and off by controlling transcription. • A promotor is a DNA segment that allows a gene to be transcribed. • An operator is a part of DNA that turns a gene “on” or “off.” • An operon includes a promoter, an operator, and one or more structural genes that code for all the proteins needed to do a job. – Operons are most common in prokaryotes. – The lac operon was one of the first examples of gene regulation to be discovered. – The lac operon has three genes that code for enzymes that break down lactose. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E • The lac operon acts like a switch. – The lac operon is “off” when lactose is not present. – The lac operon is “on” when lactose is present. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E Eukaryotes regulate gene expression at many points. • Different sets of genes are expressed in different types of cells. • Transcription is controlled by regulatory DNA sequences and protein transcription factors. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E • Transcription is controlled by regulatory DNA sequences and protein transcription factors. – Most eukaryotes have a TATA box promoter. – Enhancers and silencers speed up or slow down the rate of transcription. – Each gene has a unique combination of regulatory sequences. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E • RNA processing is also an important part of gene regulation in eukaryotes. • mRNA processing includes three major steps. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E • mRNA processing includes three major steps. – Introns are removed and exons are spliced together. – A cap is added. – A tail is added. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E Environmental factors influence gene expression, resulting in different cell types. • Internal factors can affect cell differentiation. – Uneven distribution of proteins, mRNA, and organelles within a cell can affect gene expression. – Surrounding cells can influence one another by sending and receiving signal molecules. 8.6 Gene Expression and Regulation TEKS 5C, 6C, 6D, 6E • Factors in an organism’s external environment can also affect gene expression. – Too much oxygen in an organism’s environment can prevent transcription proteins from being made by the cells. – Temperature can influence gene expression. – Drugs or chemicals in the external environment can influence cell differentiation. – Light can change the way that genes are expressed.