Role Of Gene Expression

Gene expression is the activation or "turning on" of a gene that results in transcription and the production of mRNA. Most of the mRNA produced in cells is translated into proteins. But cells do not always need to produce all of the proteins for which their genes contain instructions. Recall that proteins have many different functions. Some proteins play a structural role. Others are enzymes that act as catalysts in chemical reactions. Mechanisms to control gene expression have evolved so that each protein is produced only when it is needed.

The complete genetic material contained in an individual is called the genome (JEE-NOHM). By regulating gene expression, cells are able to control which portion of the genome will be expressed and when. Most gene expression occurs at two steps, transcription and translation. Gene expression begins when the enzyme RNA polymerase transcribes the DNA nucleotide sequence of a gene into a specific mRNA. During translation, this mRNA then migrates to a ribosome, where it is translated into a specific protein.

objectives

• Explain why cells regulate gene expression.

• Discuss the role of operons in prokaryotic gene expression.

• Determine how repressor proteins and inducers affect transcription in prokaryotes.

• Describe the structure of a eukaryotic gene.

• Compare the two ways gene expression is controlled in eukaryotes.

vocabulary gene expression genome structural gene operator operon lac operon repressor protein regulator gene inducer euchromatin intron exon pre-mRNA transcription factor enhancer

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