Control of Gene Expression

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes Gene regulation is the turning on and off of genes. Gene expression is the overall process of information flow from genes to proteins. The control of gene expression allows cells to produce specific kinds of proteins when and where they are needed. Our earliest understanding of gene control came from the study of E. coli. Student Misconceptions and Concerns  The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.7 can be a helpful reference to organize the potential sites of regulation. Teaching Tips  A key advantage of an operon system is the ability to turn off or on a set of genes with a single “switch.” You can demonstrate this relationship in your classroom by turning off or on a set of lights with a single switch.  The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type. Active Lecture Tips  The lactose operon is turned on by removing the repressor . . . a sort of double negative. Students might enjoy various analogies to other situations. Ask students in lecture to work in small groups to develop their own examples from life in which something occurs by a double negative. Share with them the common example “When the cat's away, the mice will play.” Then challenge them to each create a couple more. (Another example to consider: “Like a cat watching mice, if a mom keeps her kids away from cookies, but somebody occupies her attention, kids can sneak by and snatch some cookies. Thus, the person occupying Mom’s attention functions most like lactose binding to the repressor.”)

Figure 11.1a Figure 11.1a Cells of E. coli bacteria

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes An operon is a cluster of genes with related functions, along with the control sequences. With rare exceptions, operons only exist in prokaryotes. Student Misconceptions and Concerns  The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.7 can be a helpful reference to organize the potential sites of regulation. Teaching Tips  A key advantage of an operon system is the ability to turn off or on a set of genes with a single “switch.” You can demonstrate this relationship in your classroom by turning off or on a set of lights with a single switch.  The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type. Active Lecture Tips  The lactose operon is turned on by removing the repressor . . . a sort of double negative. Students might enjoy various analogies to other situations. Ask students in lecture to work in small groups to develop their own examples from life in which something occurs by a double negative. Share with them the common example “When the cat's away, the mice will play.” Then challenge them to each create a couple more. (Another example to consider: “Like a cat watching mice, if a mom keeps her kids away from cookies, but somebody occupies her attention, kids can sneak by and snatch some cookies. Thus, the person occupying Mom’s attention functions most like lactose binding to the repressor.”)

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes When an E. coli encounters lactose, all the enzymes needed for its metabolism are made at once using the lactose operon. The lactose (lac) operon includes three adjacent lactose-utilization genes, a promoter sequence, a site where RNA polymerase binds and initiates transcription of all three lactose genes, and an operator sequence, where a repressor can bind and block RNA polymerase action. Student Misconceptions and Concerns  The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.7 can be a helpful reference to organize the potential sites of regulation. Teaching Tips  A key advantage of an operon system is the ability to turn off or on a set of genes with a single “switch.” You can demonstrate this relationship in your classroom by turning off or on a set of lights with a single switch.  The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type. Active Lecture Tips  The lactose operon is turned on by removing the repressor . . . a sort of double negative. Students might enjoy various analogies to other situations. Ask students in lecture to work in small groups to develop their own examples from life in which something occurs by a double negative. Share with them the common example “When the cat's away, the mice will play.” Then challenge them to each create a couple more. (Another example to consider: “Like a cat watching mice, if a mom keeps her kids away from cookies, but somebody occupies her attention, kids can sneak by and snatch some cookies. Thus, the person occupying Mom’s attention functions most like lactose binding to the repressor.”)

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes E. coli uses three enzymes to take up and start metabolizing lactose only when lactose is present. The genes coding for these three enzymes are located next to each other and regulated as a single unit. Student Misconceptions and Concerns  The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.7 can be a helpful reference to organize the potential sites of regulation. Teaching Tips  A key advantage of an operon system is the ability to turn off or on a set of genes with a single “switch.” You can demonstrate this relationship in your classroom by turning off or on a set of lights with a single switch.  The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type. Active Lecture Tips  The lactose operon is turned on by removing the repressor . . . a sort of double negative. Students might enjoy various analogies to other situations. Ask students in lecture to work in small groups to develop their own examples from life in which something occurs by a double negative. Share with them the common example “When the cat's away, the mice will play.” Then challenge them to each create a couple more. (Another example to consider: “Like a cat watching mice, if a mom keeps her kids away from cookies, but somebody occupies her attention, kids can sneak by and snatch some cookies. Thus, the person occupying Mom’s attention functions most like lactose binding to the repressor.”)

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes Regulation of the lac operon A regulatory gene, located outside the operon, continually codes for a repressor protein. In the absence of lactose, the repressor binds to the operator and prevents RNA polymerase action. Lactose inactivates the repressor, so the operator is unblocked, RNA polymerase can bind to the promoter, and all three genes of the operon are transcribed. Student Misconceptions and Concerns  The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.7 can be a helpful reference to organize the potential sites of regulation. Teaching Tips  A key advantage of an operon system is the ability to turn off or on a set of genes with a single “switch.” You can demonstrate this relationship in your classroom by turning off or on a set of lights with a single switch.  The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type. Active Lecture Tips  The lactose operon is turned on by removing the repressor . . . a sort of double negative. Students might enjoy various analogies to other situations. Ask students in lecture to work in small groups to develop their own examples from life in which something occurs by a double negative. Share with them the common example “When the cat's away, the mice will play.” Then challenge them to each create a couple more. (Another example to consider: “Like a cat watching mice, if a mom keeps her kids away from cookies, but somebody occupies her attention, kids can sneak by and snatch some cookies. Thus, the person occupying Mom’s attention functions most like lactose binding to the repressor.”)

Operon turned off (lactose is absent): Figure 11.1b-0 Operon turned off (lactose is absent): OPERON Regulatory gene Promoter Operator Lactose-utilization genes DNA mRNA RNA polymerase cannot attach to the promoter Active repressor Protein Operon turned on (lactose inactivates the repressor): Figure 11.1b-0 The lac operon DNA RNA polymerase is bound to the promoter mRNA Translation Protein Lactose Inactive repressor Enzymes for lactose utilization

Operon turned off (lactose is absent): Figure 11.1b-1 Operon turned off (lactose is absent): OPERON Regulatory gene Promoter Operator Lactose-utilization genes DNA mRNA RNA polymerase cannot attach to the promoter Active repressor Protein Figure 11.1b-1 The lac operon (part 1)

Operon turned on (lactose inactivates the repressor): Figure 11.1b-2 Operon turned on (lactose inactivates the repressor): DNA RNA polymerase is bound to the promoter mRNA Translation Protein Figure 11.1b-2 The lac operon (part 2) Lactose Inactive repressor Enzymes for lactose utilization

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes There are two types of repressor-controlled operons. The lac operon is an example of an inducible operon that is usually turned off but can be stimulated (induced) by a molecule—in this case, by lactose. The trp operon is an example of a repressible operon that is normally turned on but can be inhibited (repressed) when a specific molecule (such as amino acid tryptophan) is present in abundance. Student Misconceptions and Concerns  The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.7 can be a helpful reference to organize the potential sites of regulation. Teaching Tips  A key advantage of an operon system is the ability to turn off or on a set of genes with a single “switch.” You can demonstrate this relationship in your classroom by turning off or on a set of lights with a single switch.  The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type. Active Lecture Tips  The lactose operon is turned on by removing the repressor . . . a sort of double negative. Students might enjoy various analogies to other situations. Ask students in lecture to work in small groups to develop their own examples from life in which something occurs by a double negative. Share with them the common example “When the cat's away, the mice will play.” Then challenge them to each create a couple more. (Another example to consider: “Like a cat watching mice, if a mom keeps her kids away from cookies, but somebody occupies her attention, kids can sneak by and snatch some cookies. Thus, the person occupying Mom’s attention functions most like lactose binding to the repressor.”)

lac operon (inducible) trp operon (repressible) Figure 11.1c lac operon (inducible) trp operon (repressible) Promoter Operator Gene DNA Active repressor Active repressor Tryptophan Figure 11.1c Two types of repressor-controlled operons Inactive repressor Inactive repressor Lactose

11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes Another type of operon control involves activators, proteins that turn operons on by binding to DNA and stimulating gene transcription. Activators help control a wide variety of operons. Student Misconceptions and Concerns  The broad concept of selective reading of the genetic code associated with differentiation and types of cellular activity can be missed when concentrating on the extensive details of regulation. Analogies, noted below in the teaching tips, can help students relate this overall selective process to their own experiences. Students already understand the selective reading of relevant chapters in textbooks and the selective referencing of software manuals to get answers to different questions. These experiences are similar in many ways to the broad processes of gene regulation. The many levels of gene regulation in eukaryotic cells can be confusing and frustrating. The water pipe analogy depicted in Figure 11.7 can be a helpful reference to organize the potential sites of regulation. Teaching Tips  A key advantage of an operon system is the ability to turn off or on a set of genes with a single “switch.” You can demonstrate this relationship in your classroom by turning off or on a set of lights with a single switch.  The control of gene expression is analogous to buying a book about how to build birdhouses and reading only the plans needed to build one particular model. Although the book contains directions to build many different birdhouses, you read and follow only the directions for the particular birdhouse you choose to build. The pages and directions for the other birdhouses remain intact. When cells differentiate, they read, or express, only the genes that are needed in that particular cell type. Active Lecture Tips  The lactose operon is turned on by removing the repressor . . . a sort of double negative. Students might enjoy various analogies to other situations. Ask students in lecture to work in small groups to develop their own examples from life in which something occurs by a double negative. Share with them the common example “When the cat's away, the mice will play.” Then challenge them to each create a couple more. (Another example to consider: “Like a cat watching mice, if a mom keeps her kids away from cookies, but somebody occupies her attention, kids can sneak by and snatch some cookies. Thus, the person occupying Mom’s attention functions most like lactose binding to the repressor.”)