1. Concept 18.5: Cancer results from genetic changes that affect cell cycle control
The gene regulation systems that go wrong during cancer are the very same systems involved in embryonic development

2. Types of Genes Associated with Cancer
Cancer can be caused by mutations to genes that regulate cell growth and division
Tumor viruses can cause cancer in animals including humans

3. Oncogenes and Proto-Oncogenes
Oncogenes are cancer-causing genes
Proto-oncogenes are the corresponding normal cellular genes that are responsible for normal cell growth and division
Conversion of a proto-oncogene to an oncogene can lead to abnormal stimulation of the cell cycle

4. within a control element within the gene
Fig
Proto-oncogene
DNA
Translocation or
transposition:
Gene amplification:
Point mutation:
within a control element
within the gene
New
promoter
Oncogene
Oncogene
Figure Genetic changes that can turn proto-oncogenes into oncogenes
Normal growth-
stimulating
protein in excess
Normal growth-stimulating
protein in excess
Normal growth-
stimulating
protein in excess
Hyperactive or
degradation-
resistant protein

5. Proto-oncogenes can be converted to oncogenes by
Movement of DNA within the genome: if it ends up near an active promoter, transcription may increase
Amplification of a proto-oncogene: increases the number of copies of the gene
Point mutations in the proto-oncogene or its control elements: causes an increase in gene expression

6. Tumor-Suppressor Genes
Tumor-suppressor genes help prevent uncontrolled cell growth
Mutations that decrease protein products of tumor-suppressor genes may contribute to cancer onset
Tumor-suppressor proteins
Repair damaged DNA
Control cell adhesion
Inhibit the cell cycle in the cell-signaling pathway

7. Interference with Normal Cell-Signaling Pathways
Mutations in the ras proto-oncogene and p53 tumor-suppressor gene are common in human cancers
Mutations in the ras gene can lead to production of a hyperactive Ras protein and increased cell division

8. Figure 18.21 Signaling pathways that regulate cell division
Growth
factor
MUTATION
Hyperactive
Ras protein
(product of
oncogene)
issues
signals
on its own
Ras 3
G protein
GTP
Ras
GTP 2
Receptor 4
Protein kinases
(phosphorylation
cascade)
NUCLEUS 5
Transcription
factor (activator)
DNA
Gene expression
Protein that
stimulates
the cell cycle
(a) Cell cycle–stimulating pathway 2
Protein kinases
MUTATION
Defective or
missing
transcription
factor, such
as p53, cannot
activate UV
light 3
Active
form
of p53 1
DNA damage
in genome
Figure Signaling pathways that regulate cell division
DNA
Protein that
inhibits
the cell cycle
(b) Cell cycle–inhibiting pathway
EFFECTS OF MUTATIONS
Protein
overexpressed
Protein absent
Cell cycle
overstimulated
Increased cell
division
Cell cycle not
inhibited
(c) Effects of mutations

9. (a) Cell cycle–stimulating pathway
Fig a 1
Growth
factor 1
MUTATION
Hyperactive
Ras protein
(product of
oncogene)
issues
signals
on its own
Ras 3
G protein
GTP
Ras
GTP 2
Receptor 4
Protein kinases
(phosphorylation
cascade)
NUCLEUS 5
Transcription
factor (activator)
DNA
Figure Signaling pathways that regulate cell division
Gene expression
Protein that
stimulates
the cell cycle
(a) Cell cycle–stimulating pathway

10. (b) Cell cycle–inhibiting pathway
Fig b 2
Protein kinases
MUTATION
Defective or
missing
transcription
factor, such
as p53, cannot
activate 3
Active
form
of p53 UV
light 1
DNA damage
in genome
DNA
Figure Signaling pathways that regulate cell division
Protein that
inhibits
the cell cycle
(b) Cell cycle–inhibiting pathway

11. (c) Effects of mutations
Fig c
EFFECTS OF MUTATIONS
Protein
overexpressed
Protein absent
Cell cycle
overstimulated
Increased cell
division
Cell cycle not
inhibited
Figure Signaling pathways that regulate cell division
(c) Effects of mutations

12. Suppression of the cell cycle can be important in the case of damage to a cell’s DNA; p53 prevents a cell from passing on mutations due to DNA damage
Mutations in the p53 gene prevent suppression of the cell cycle

13. The Multistep Model of Cancer Development
Multiple mutations are generally needed for full-fledged cancer; thus the incidence increases with age
At the DNA level, a cancerous cell is usually characterized by at least one active oncogene and the mutation of several tumor-suppressor genes

14. EFFECTS OF MUTATIONS Fig. 18-22
Colon
EFFECTS OF MUTATIONS
Loss of tumor-
suppressor gene
APC (or other) 1
Activation of
ras oncogene 2
Loss of
tumor-suppressor
gene p53 4
Colon wall
Loss of
tumor-suppressor
gene DCC 3
Additional
mutations 5
Figure A multistep model for the development of colorectal cancer
Normal colon
epithelial cells
Small benign
growth (polyp)
Larger benign
growth (adenoma)
Malignant tumor
(carcinoma)

15. Colon Colon wall Normal colon epithelial cells Fig. 18-22a
Figure A multistep model for the development of colorectal cancer
Normal colon
epithelial cells

16. 1 Small benign growth (polyp) Loss of tumor- suppressor gene
Fig b
Loss of tumor-
suppressor gene
APC (or other) 1
Small benign
growth (polyp)
Figure A multistep model for the development of colorectal cancer

17. Activation of ras oncogene 2 3 Larger benign growth (adenoma) Loss of
Fig c
Activation of
ras oncogene 2
Loss of
tumor-suppressor
gene DCC 3
Larger benign
growth (adenoma)
Figure A multistep model for the development of colorectal cancer

18. Additional mutations Malignant tumor (carcinoma) Loss of 4
Fig d
Loss of
tumor-suppressor
gene p53 4
Additional
mutations 5
Malignant tumor
(carcinoma)
Figure A multistep model for the development of colorectal cancer

19. Inherited Predisposition and Other Factors Contributing to Cancer
Individuals can inherit oncogenes or mutant alleles of tumor-suppressor genes
Inherited mutations in the tumor-suppressor gene adenomatous polyposis coli are common in individuals with colorectal cancer
Mutations in the BRCA1 or BRCA2 gene are found in at least half of inherited breast cancers

20. Fig
Figure Tracking the molecular basis of breast cancer

21. Operon Promoter Genes A B C Operator RNA polymerase A B C Polypeptides
Fig. 18-UN1
Operon
Promoter
Genes A B C
Operator
RNA
polymerase
Fig. 18-UN1 A B C
Polypeptides

22. no corepressor present Corepressor
Fig. 18-UN2
Genes expressed
Genes not expressed
Promoter
Genes
Operator
Active repressor:
corepressor bound
Inactive repressor:
no corepressor present
Corepressor
Fig. 18-UN2

23. Genes not expressed Genes expressed Promoter Operator Genes
Fig. 18-UN3
Genes not expressed
Genes expressed
Promoter
Operator
Genes
Fig. 18-UN2
Active repressor:
no inducer present
Inactive repressor:
inducer bound
Fig. 18-UN3

24. Protein processing and degradation
Fig. 18-UN4
Chromatin modification
Transcription
• Genes in highly compacted
chromatin are generally not
transcribed.
• Regulation of transcription initiation:
DNA control elements bind specific
transcription factors.
• Histone acetylation seems to
loosen chromatin structure,
enhancing transcription.
Bending of the DNA enables activators to
contact proteins at the promoter, initiating
transcription.
• DNA methylation generally
reduces transcription.
• Coordinate regulation:
Enhancer for
liver-specific genes
Enhancer for
lens-specific genes
Chromatin modification
Transcription
RNA processing
• Alternative RNA splicing:
RNA processing
Primary RNA
transcript
mRNA
degradation
Translation
mRNA or
Fig. 18-UN4
Protein processing
and degradation
Translation
• Initiation of translation can be controlled
via regulation of initiation factors.
mRNA degradation
• Each mRNA has a
characteristic life span,
determined in part by
sequences in the 5 and
3 UTRs.
Protein processing and degradation
• Protein processing and
degradation by proteasomes
are subject to regulation.

25. Chromatin modification
Fig. 18-UN5
Chromatin modification
• Small RNAs can promote the formation of
heterochromatin in certain regions, blocking
transcription.
Chromatin modification
Transcription
Translation
RNA processing
• miRNA or siRNA can block the translation
of specific mRNAs.
mRNA
degradation
Translation
Protein processing
and degradation
Fig. 18-UN5
mRNA degradation
• miRNA or siRNA can target specific mRNAs
for destruction.

26. Enhancer Promoter Gene 1 Gene 2 Gene 3 Gene 4 Gene 5
Fig. 18-UN6
Enhancer
Promoter
Gene 1
Gene 2
Gene 3
Fig. 18-UN6
Gene 4
Gene 5

27. Fig. 18-UN7
Fig. 18-UN7

28. Fig. 18-UN8
Fig. 18-UN8

29. You should now be able to:
Explain the concept of an operon and the function of the operator, repressor, and corepressor
Explain the adaptive advantage of grouping bacterial genes into an operon
Explain how repressible and inducible operons differ and how those differences reflect differences in the pathways they control

30. Explain how DNA methylation and histone acetylation affect chromatin structure and the regulation of transcription
Define control elements and explain how they influence transcription
Explain the role of promoters, enhancers, activators, and repressors in transcription control

31. Explain how eukaryotic genes can be coordinately expressed
Describe the roles played by small RNAs on gene expression
Explain why determination precedes differentiation
Describe two sources of information that instruct a cell to express genes at the appropriate time

32. Explain how maternal effect genes affect polarity and development in Drosophila embryos
Explain how mutations in tumor-suppressor genes can contribute to cancer
Describe the effects of mutations to the p53 and ras genes