1. How Genes Are Controlled
Chapter 11
How Genes Are Controlled

2. Control of Gene Expression Cloning of Plants and Animals
Figure 11.0_1
Chapter 11: Big Ideas
Control of Gene Expression
Cloning of Plants and Animals
Figure 11.0_1 Chapter 11: Big Ideas
The Genetic Basis of Cancer 2

3. CONTROL OF GENE EXPRESSION
E. Coli bacteria
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4. 11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes
Gene expression is the overall process of information flow from genes to proteins.
Gene regulation is the turning on and off of genes.
Why is that gene expression has to be regulated?
Student Misconceptions and Concerns
1. 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.
2. 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
1. The lactose operon is turned on by removing the repressor a sort of double negative. Students might enjoy various analogies to other situations, including the familiar refrain “When the cat's away, the mice will play.” 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.
2. 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.
3. 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.
© 2012 Pearson Education, Inc. 4

5. 11.1 Proteins interacting with DNA turn prokaryotic genes on or off in response to environmental changes
The control of gene expression allows cells to produce specific kinds of proteins when and where they are needed.
Gene regulation can help organism respond to environmental changes
Skip the lac operon
Student Misconceptions and Concerns
1. 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.
2. 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
1. The lactose operon is turned on by removing the repressor a sort of double negative. Students might enjoy various analogies to other situations, including the familiar refrain “When the cat's away, the mice will play.” 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.
2. 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.
3. 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.
© 2012 Pearson Education, Inc. 5

6. 11.2 Chromosome structure and chemical modifications can affect gene expression
Differentiation
Almost all of the cells in an organism contain an identical genome.
The differences between cell types are not due to the presence of different genes but instead due to selective gene expression.
Humans have about 25,000 genes and only a fraction of these genes are used or expressed in each cell involves cell specialization, in structure and function, and
Differentiation is controlled by turning specific sets of genes on or off.
Student Misconceptions and Concerns
1. 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.
2. 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
1. 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.
2. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
3. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.
4. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.
© 2012 Pearson Education, Inc. 6

7. Some types of human cells. All cells have the same DNA
Some types of human cells. All cells have the same DNA
Figure 11.2 Some types of human cells.
This figure compares the appearance of muscle, pancreas, and blood cells. It can be used to emphasize that different genes are active in each cell type, coding for the specific proteins related to the function of the cell.
In muscle cells, proteins such as actin and myosin that are responsible for contraction are produced.
Insulin is produced in beta cells of the pancreas while glucagon is produced in alpha cells.
Hemoglobin is produced in tremendous quantities in red blood cells.
Muscle cell
Pancreas cells
Blood cells

8. 11.2 Chromosome structure and chemical modifications can affect gene expression
How gene expression is regulated
DNA packing
Epigenetic modifications
X chromosome inactivation
Control of gene expression by RNA (11.5)
Student Misconceptions and Concerns
1. 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.
2. 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
1. 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.
2. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
3. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.
4. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.
© 2012 Pearson Education, Inc. 8

9. 11.2 Chromosome structure and chemical modifications can affect gene expression
DNA packing
Eukaryotic chromosomes undergo multiple levels of folding and coiling, called DNA packing.
Nucleosomes are formed when DNA is wrapped around histone proteins. (This packaging gives a “beads on a string” appearance. Each nucleosome bead includes DNA plus eight histones. Stretches of DNA, called linkers, join consecutive nucleosomes.)
At the next level of packing, the beaded string is wrapped into a tight helical fiber. This fiber coils further into a thick supercoil.
Looping and folding can further compact the DNA.
Student Misconceptions and Concerns
1. 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.
2. 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
1. 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.
2. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
3. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.
4. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.
© 2012 Pearson Education, Inc. 9

10. DNA double helix (2-nm diameter)
Figure 11.2A
DNA packing in a eukaryotic chromosome
DNA double helix (2-nm diameter)
Metaphase chromosome
Nucleosome (10-nm diameter)
Tight helical fiber (30-nm diameter)
Linker
“Beads on a string”
Figure 11.2A DNA packing in a eukaryotic chromosome
Supercoil (300-nm diameter)
Histones
700 nm 10

11. 11.2 Chromosome structure and chemical modifications can affect gene expression
DNA packing
Can prevent gene expression by preventing RNA polymerase and other transcription proteins from contacting the DNA.
Cells seem to use higher levels of packing for long- term inactivation of genes.
Highly compacted chromatin, found in varying regions of interphase chromosomes, is generally not expressed at all.
Student Misconceptions and Concerns
1. 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.
2. 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
1. 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.
2. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
3. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.
4. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.
© 2012 Pearson Education, Inc. 11

12. 11.2 Chromosome structure and chemical modifications can affect gene expression
Epigenetic modifications
Chemical modification of DNA bases
And modification of histone proteins
Certain enzymes can add a methyl group to DNA bases, without changing the sequence of the bases.
Individual genes are usually more methylated in cells in which the genes are not expressed. Once methylated, genes usually stay that way through successive cell divisions in an individual.
Student Misconceptions and Concerns
1. 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.
2. 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
1. 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.
2. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
3. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.
4. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.
© 2012 Pearson Education, Inc. 12

13. 11.2 Chromosome structure and chemical modifications can affect gene expression
Epigenetic modifications
Removal of the extra methyl groups can turn on some of these genes.
Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence is called epigenetic inheritance. These modifications can be reversed by processes not yet fully understood.
Potential for drug development based on epigenetics
More from the video “Ghost in your genes”
Student Misconceptions and Concerns
1. 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.
2. 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
1. 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.
2. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
3. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.
4. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.
© 2012 Pearson Education, Inc. 13

14. 11.2 Chromosome structure and chemical modifications can affect gene expression
X-chromosome inactivation
In female mammals, one of the two X chromosomes is highly compacted and transcriptionally inactive.
Either the maternal or paternal chromosome is randomly inactivated.
Inactivation occurs early in embryonic development, and all cellular descendants have the same inactivated chromosome.
An inactivated X chromosome is called a Barr body.
Tortoiseshell fur coloration is due to inactivation of X chromosomes in heterozygous female cats.
Student Misconceptions and Concerns
1. 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.
2. 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
1. 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.
2. Just as boxes of things that you rarely use are packed into a closet, attic, or basement, chromatin that is not expressed is highly compacted, and stored deeply packed away.
3. Just as a folded map is difficult to read, DNA packaging tends to prevent gene reading or expression.
4. Students might wonder why a patch of color is all the same on a cat’s skin if every cell has an equal chance of being one of the two color forms. The answer is that X chromosome inactivation occurs early in development. Thus, the patch of one color represents the progeny of one embryonic cell after X chromosome inactivation.
© 2012 Pearson Education, Inc. 14

15. Cell division and random X chromosome inactivation
Figure 11.2B
A tortoiseshell pattern on a female cat, a result of X chromosome inactivation
Early Embryo
Adult
Two cell populations
Cell division and random X chromosome inactivation
X chromo- somes
Active X
Orange fur
Inactive X
Figure 11.2B A tortoiseshell pattern on a female cat, a result of X chromosome inactivation
Allele for orange fur
Inactive X
Allele for black fur
Active X
Black fur 15

16. 11.5 Small RNAs play multiple roles in controlling gene expression
Small RNAs control gene expression
Only about 1.5% of the human genome codes for proteins. (This is also true of many other multicellular eukaryotes.)
Another small fraction of DNA consists of genes for ribosomal RNA and transfer RNA.
A flood of recent data suggests that a significant amount of the remaining DNA is transcribed into functioning but non-protein-coding RNAs, including a variety of small RNAs.
Student Misconceptions and Concerns
1. 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.
2. 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
1. References in older books and outdated websites may characterize DNA that does not code for rRNA, tRNA, or mRNA as junk DNA. The relatively recent discovery of miRNA and its significant roles in gene regulation reveals the danger of concluding that the absence of evidence is evidence of absence!
2. Describing the discovery of miRNAs and their potential in research and medicine helps to illustrate the promise of gene regulation research. Students early in their science careers may appreciate knowing about scientific fields with great potential as they consider the direction of their developing careers.
© 2012 Pearson Education, Inc. 16

17. 11.5 Small RNAs play multiple roles in controlling gene expression
microRNAs (miRNAs) can bind to complementary sequences on mRNA molecules either
degrading the target mRNA or
blocking its translation.
RNA interference (RNAi) is the use of miRNA to artificially control gene expression by injecting miRNAs into a cell to turn off a specific gene sequence.
Student Misconceptions and Concerns
1. 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.
2. 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
1. References in older books and outdated websites may characterize DNA that does not code for rRNA, tRNA, or mRNA as junk DNA. The relatively recent discovery of miRNA and its significant roles in gene regulation reveals the danger of concluding that the absence of evidence is evidence of absence!
2. Describing the discovery of miRNAs and their potential in research and medicine helps to illustrate the promise of gene regulation research. Students early in their science careers may appreciate knowing about scientific fields with great potential as they consider the direction of their developing careers.
© 2012 Pearson Education, Inc. 17

18. RNA interference Protein miRNA miRNA- protein complex Target mRNA or
Figure 11.5
Protein
miRNA 1
RNA interference
miRNA- protein complex 2
Target mRNA
Figure 11.5 Mechanisms of RNA interference 3 or 4
Translation blocked
mRNA degraded 18

19. 11.5 Small RNAs play multiple roles in controlling gene expression
Question: If a gene has a sequence of AATTCGCG, design an miRNA piece that can inactivate the gene
Student Misconceptions and Concerns
1. 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.
2. 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
1. References in older books and outdated websites may characterize DNA that does not code for rRNA, tRNA, or mRNA as junk DNA. The relatively recent discovery of miRNA and its significant roles in gene regulation reveals the danger of concluding that the absence of evidence is evidence of absence!
2. Describing the discovery of miRNAs and their potential in research and medicine helps to illustrate the promise of gene regulation research. Students early in their science careers may appreciate knowing about scientific fields with great potential as they consider the direction of their developing careers.
© 2012 Pearson Education, Inc. 19

20. THE GENETIC BASIS OF CANCER
© 2012 Pearson Education, Inc. 20

21. 11.16 Cancer results from mutations in genes that control cell division
Cancer is a disease of damaged DNA
Every time a cell divides, it must accurately copy its DNA. It is estimated that 100 million million cell divisions take place during an average human life time.
Every cell has the potential to introduce a mutation (an error) into a daughter cell
Although many mutations are harmless, when mutation takes place in a critical gene, the normal cell can be turned into a cancerous cell.
Student Misconceptions and Concerns
Students typically have little background knowledge of cancer at the cellular level. Consider creating your own pre-test to inquire about your students’ entering knowledge of cancer. For example, ask students if all cancers are genetic (yes, all cancers are based upon genetic errors and are the main subject of this chapter). In addition, ask students if exposure to a virus can lead to cancer. (Answer: yes, as noted in Module 11.16).
Teaching Tips
1. Tumor-suppressor genes function like the repressor in the E. coli lactose operon. The lac operon is expressed, and cancers appear when their respective repressors do not function.
2. The production of a vaccine (Gardasil) against a virus known to contribute to cervical cancer has helped students become aware of the risks of HPV exposure. The website of the National Cancer Institute describes the risks of HPV infection at
© 2012 Pearson Education, Inc. 21

22. Mutations in two types of genes can lead to cancer
11.16 Cancer results from mutations in genes that control cell division
Mutations in two types of genes can lead to cancer
Proto-oncogenes
Tumor suppresor genes
Student Misconceptions and Concerns
Students typically have little background knowledge of cancer at the cellular level. Consider creating your own pre-test to inquire about your students’ entering knowledge of cancer. For example, ask students if all cancers are genetic (yes, all cancers are based upon genetic errors and are the main subject of this chapter). In addition, ask students if exposure to a virus can lead to cancer. (Answer: yes, as noted in Module 11.16).
Teaching Tips
1. Tumor-suppressor genes function like the repressor in the E. coli lactose operon. The lac operon is expressed, and cancers appear when their respective repressors do not function.
2. The production of a vaccine (Gardasil) against a virus known to contribute to cervical cancer has helped students become aware of the risks of HPV exposure. The website of the National Cancer Institute describes the risks of HPV infection at
© 2012 Pearson Education, Inc. 22

23. 11.16 Cancer results from mutations in genes that control cell division
Oncogenes
Proto-oncogenes are normal genes that stimulate cell division.
Mutations in proto-oncogenes can turn them into cancer-causing oncogenes
A cell can acquire an oncogene from a mutated proto-oncogene or from viruses, eg: cervical cancer
A gene called ras is a proto-oncogene. Mutations in ras occur in more than 30% of human cancers.
Student Misconceptions and Concerns
Students typically have little background knowledge of cancer at the cellular level. Consider creating your own pre-test to inquire about your students’ entering knowledge of cancer. For example, ask students if all cancers are genetic (yes, all cancers are based upon genetic errors and are the main subject of this chapter). In addition, ask students if exposure to a virus can lead to cancer. (Answer: yes, as noted in Module 11.16).
Teaching Tips
1. Tumor-suppressor genes function like the repressor in the E. coli lactose operon. The lac operon is expressed, and cancers appear when their respective repressors do not function.
2. The production of a vaccine (Gardasil) against a virus known to contribute to cervical cancer has helped students become aware of the risks of HPV exposure. The website of the National Cancer Institute describes the risks of HPV infection at
© 2012 Pearson Education, Inc. 23

24. Proto-oncogene (for a protein that stimulates cell division)
Figure 11.16A
Proto-oncogene (for a protein that stimulates cell division)
DNA
A mutation within the gene
Multiple copies of the gene
The gene is moved to a new DNA locus, under new controls
Oncogene
New promoter
Figure 11.16A Alternative ways to make oncogenes from a proto-oncogene (all leading to excessive cell growth)
Hyperactive growth- stimulating protein in a normal amount
Normal growth- stimulating protein in excess
Normal growth- stimulating protein in excess 24

25. Tumor-suppressor genes
11.16 Cancer results from mutations in genes that control cell division
Tumor-suppressor genes
Tumor-suppressor genes normally inhibit cell division or function in the repair of DNA damage.
Mutations inactivate the genes and allow uncontrolled division to occur.
Eg: p53 is tumor suppressor gene mutated in almost a half of all human cancers
Mutations in BRCA1 and BRCA2 can lead to breast cancer
Policemen of the genome
Student Misconceptions and Concerns
Students typically have little background knowledge of cancer at the cellular level. Consider creating your own pre-test to inquire about your students’ entering knowledge of cancer. For example, ask students if all cancers are genetic (yes, all cancers are based upon genetic errors and are the main subject of this chapter). In addition, ask students if exposure to a virus can lead to cancer. (Answer: yes, as noted in Module 11.16).
Teaching Tips
1. Tumor-suppressor genes function like the repressor in the E. coli lactose operon. The lac operon is expressed, and cancers appear when their respective repressors do not function.
2. The production of a vaccine (Gardasil) against a virus known to contribute to cervical cancer has helped students become aware of the risks of HPV exposure. The website of the National Cancer Institute describes the risks of HPV infection at
© 2012 Pearson Education, Inc. 25

26. Tumor-suppressor gene Mutated tumor-suppressor gene
Figure 11.16B
Tumor-suppressor gene
Mutated tumor-suppressor gene
Normal growth- inhibiting protein
Defective, nonfunctioning protein
Cell division not under control
Cell division under control
Figure 11.16B The effect of a mutation in a tumor-suppressor gene 26

27. 11.17 Multiple genetic changes underlie the development of cancer
Usually four or more somatic mutations are required to turn a normal cell into a full-fledged cancer cell.
One possible scenario is the stepwise development of colorectal cancer.
An oncogene is activated, resulting in increased cell division in apparently normal cells in the colon lining.
Additional DNA mutations cause the growth of a small benign tumor (polyp) in the colon wall.
Additional mutations lead to a malignant tumor with the potential to metastasize.
Teaching Tips
Exposure to carcinogens early in life carries greater risks than the same exposure later in life. This is because damage in early life has more time to accumulate additional changes, potentially leading to disease.
© 2012 Pearson Education, Inc. 27

28. Accumulation of mutations in the development of a cancer cell
Figure 11.17B
Accumulation of mutations in the development of a cancer cell
1 mutation
2 mutations
3 mutations
4 mutations
Chromosomes
Normal cell
Malignant cell
Figure 11.17B Accumulation of mutations in the development of a cancer cell 28

29. Stepwise development of a typical colon cancer
Figure 11.17A
Stepwise development of a typical colon cancer
DNA changes:
An oncogene is activated
A tumor-suppressor gene is inactivated
A second tumor- suppressor gene is inactivated
Cellular changes:
Increased cell division
Growth of a polyp
Growth of a malignant tumor 1 2 3
Figure 11.17A Stepwise development of a typical colon cancer
Colon wall 29

30. 11.19 CONNECTION: Lifestyle choices can reduce the risk of cancer
After heart disease, cancer is the second-leading cause of death in most industrialized nations.
Cancer is not one disease, but a group of more than 200 (see table for a partial list)
All cancers are ultimately diseases of our genes
Cancer can run in families if an individual inherits an oncogene or a mutant allele of a tumor-suppressor gene that makes cancer one step closer.
But most cancers cannot be associated with an inherited mutation.
Student Misconceptions and Concerns
Many students do not appreciate the increased risk of skin cancer associated with the use of tanning beds, which is still popular with many college-age populations.
Teaching Tips
1. Students may not realize the possible consequences of testing positive for a predisposition to cancer. Health insurance companies could use that information to deny insurance to people who are more likely to get ill. Furthermore, people may feel obliged or be obligated to share this information with a potential mate or employer.
2. Nearly one in five deaths in the United States results from the use of tobacco. Additional information on the risks of tobacco can be found at the website for the American Cancer Society at
© 2012 Pearson Education, Inc. 30

31. Table 11.19
Table Cancer in the United States 31

32. 11.19 CONNECTION: Lifestyle choices can reduce the risk of cancer
Carcinogens are cancer-causing agents that alter DNA.
Most mutagens (substances that promote mutations) are carcinogens.
Two of the most potent carcinogens (mutagens) are
X-rays and
ultraviolet radiation in sunlight.
Student Misconceptions and Concerns
Many students do not appreciate the increased risk of skin cancer associated with the use of tanning beds, which is still popular with many college-age populations.
Teaching Tips
1. Students may not realize the possible consequences of testing positive for a predisposition to cancer. Health insurance companies could use that information to deny insurance to people who are more likely to get ill. Furthermore, people may feel obliged or be obligated to share this information with a potential mate or employer.
2. Nearly one in five deaths in the United States results from the use of tobacco. Additional information on the risks of tobacco can be found at the website for the American Cancer Society at
© 2012 Pearson Education, Inc. 32

33. 11.19 CONNECTION: Lifestyle choices can reduce the risk of cancer
The one substance known to cause more cases and types of cancer than any other single agent is tobacco.
More people die of lung cancer than any other form of cancer.
Although most tobacco-related cancers come from smoking, passive inhalation of second-hand smoke is also a risk.
Tobacco use, sometimes in combination with alcohol consumption, causes cancers in addition to lung cancer.
Student Misconceptions and Concerns
Many students do not appreciate the increased risk of skin cancer associated with the use of tanning beds, which is still popular with many college-age populations.
Teaching Tips
1. Students may not realize the possible consequences of testing positive for a predisposition to cancer. Health insurance companies could use that information to deny insurance to people who are more likely to get ill. Furthermore, people may feel obliged or be obligated to share this information with a potential mate or employer.
2. Nearly one in five deaths in the United States results from the use of tobacco. Additional information on the risks of tobacco can be found at the website for the American Cancer Society at
© 2012 Pearson Education, Inc. 33

34. 11.19 CONNECTION: Lifestyle choices can reduce the risk of cancer
Healthy lifestyles that reduce the risks of cancer include
avoiding carcinogens, including chemicals, the sun and tanning beds
avoiding tobacco products,
exercising adequately,
regular medical checks for common types of cancer, and
a healthy high-fiber, low-fat diet including plenty of fruits and vegetables.
Student Misconceptions and Concerns
Many students do not appreciate the increased risk of skin cancer associated with the use of tanning beds, which is still popular with many college-age populations.
Teaching Tips
1. Students may not realize the possible consequences of testing positive for a predisposition to cancer. Health insurance companies could use that information to deny insurance to people who are more likely to get ill. Furthermore, people may feel obliged or be obligated to share this information with a potential mate or employer.
2. Nearly one in five deaths in the United States results from the use of tobacco. Additional information on the risks of tobacco can be found at the website for the American Cancer Society at
© 2012 Pearson Education, Inc. 34