Regulation of Gene Expression

Page
15

factor, such

as p53, cannot

activate

transcription

Protein that

inhibits

the cell cycle

Active

form

of p53

UV

light

(b) Cell cycle–inhibiting pathway

2

3

1

Slide 105

Fig. 18-21c

(c) Effects of mutations

EFFECTS OF MUTATIONS

Cell cycle not

inhibited

Protein absent

Increased cell

division

Protein

overexpressed

Cell cycle

overstimulated

Slide 106

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

Slide 107

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

Slide 108

Fig. 18-22

EFFECTS OF MUTATIONS

Malignant tumor

(carcinoma)

Colon

Colon wall

Loss of tumor-

suppressor gene

APC (or other)

Activation of

ras oncogene

Loss of

tumor-suppressor

gene DCC

Loss of

tumor-suppressor

gene p53

Additional

mutations

Larger benign

growth (adenoma)

Small benign

growth (polyp)

Normal colon

epithelial cells

5

4

2

3

1

Slide 109

Fig. 18-22a

Colon

Colon wall

Normal colon

epithelial cells

Slide 110

Fig. 18-22b

Loss of tumor-

suppressor gene

APC (or other)

Small benign

growth (polyp)

1

Slide 111

Fig. 18-22c

Activation of

ras oncogene

Loss of

tumor-suppressor

gene DCC

Larger benign

growth (adenoma)

2

3

Slide 112

Fig. 18-22d

Malignant tumor

(carcinoma)

Loss of

tumor-suppressor

gene p53

Additional

mutations

5

4

Slide 113

Inherited Predisposition and Other Factors Contributing to Cancer

Individuals can inherit oncogenes or mutant alleles of tumor-suppressor genes