Cancer and Genetics

1
Cancer and Genetics

• Concept 19.3 Cancer results from genetic changes
  that affect cell cycle control
• The gene regulation systems that go wrong during
  cancer
• Turn out to be the very same systems that play
  important roles in embryonic development

2
Types of Genes Associated with Cancer

• The genes that normally regulate cell growth and
  division during the cell cycle
• Include genes for growth factors, their
  receptors, and the intracellular molecules of
  signaling pathways

3
Oncogenes and Proto-Oncogenes

• Oncogenes
• Are cancer-causing genes
• Proto-oncogenes
• Are normal cellular genes that code for proteins
  that stimulate normal cell growth and division

4

• A DNA change that makes a proto-oncogene
  excessively active
• Converts it to an oncogene, which may promote
  excessive cell division and cancer

Figure 19.11
5
Tumor-Suppressor Genes

• Tumor-suppressor genes
• Encode proteins that inhibit abnormal cell
  division

6
Interference with Normal Cell-Signaling Pathways

• Many proto-oncogenes and tumor suppressor genes
• Encode components of growth-stimulating and
  growth-inhibiting pathways, respectively

7

• The p53 gene encodes a tumor-suppressor protein
• That is a specific transcription factor that
  promotes the synthesis of cell cycleinhibiting
  proteins

Figure 19.12b
8

• Mutations that knock out the p53 gene
• Can lead to excessive cell growth and cancer

(c)
Effects of mutations. Increased cell division,
possibly leading to cancer, can result if the
cell cycle is overstimulated, as in (a), or not
inhibited when it normally would be, as in (b).
EFFECTS OF MUTATIONS
Protein overexpressed
Protein absent
Cell cycle not inhibited
Cell cycle overstimulated
Increased cell division
Figure 19.12c
9
The Multistep Model of Cancer Development

• Normal cells are converted to cancer cells
• By the accumulation of multiple mutations
  affecting proto-oncogenes and tumor-suppressor
  genes

10

• Certain viruses
• Promote cancer by integration of viral DNA into a
  cells genome

11
Inherited Predisposition to Cancer

• Individuals who inherit a mutant oncogene or
  tumor-suppressor allele
• Have an increased risk of developing certain
  types of cancer