Cancer and
Gene Regulation
Chapter 18, Section 5
I.
Cell Cycle is controlled by genes
A. Many genes make proteins that regulate when
a cell grows. (what we learned, what really happens)
~examples of proteins – growth factors, cell
receptors for growth factors, transcription factors
B. Mutations to any gene involved in the cell cycle can
cause cancer
~Causes of mutations include
1. spontaneous during DNA replication
2. chemicals from environment, x-rays, viruses
II. Gene types that cause cancer
A. Proto-oncogene – normal gene that codes for
proteins that control normal cell growth and division
mutates and becomes an
oncogene – cancer-causing gene; abnormal cell cycle

Example – Ras gene
Oncogenes are
PERMANENTLY
ON ! This means
that proteins
that start cell
division are
ALWAYS BEING
MADE ACTIVE.
This is like
pressing the gas
pedal to its
maximum ALL
THE TIME.
Found in 30% of
all tested cancer
cells.
B. Tumor Suppressor genes – normal genes that help
prevent uncontrolled cell growth by
1. Making proteins that initiate repair of damaged DNA
2. Stopping over-damaged cells from dividing and
initiating apoptosis
-when these genes are turned on they functions normally

Example – p53 gene, aka Guardian of the Genome 
Mutation in tumor
suppressor gene
turns the gene
OFF, allowing all
cells, normal and
damaged, to
divide.
Cell stopped
from dividing
This is like taking
the brake pedal
away…thus you
never stop!
*Found in 50% of
all tested cancer
cells
Cell divides with
DNA damage
III. Predispositions to Cancer
A. It takes multiple mutations (~6 or more) within
cell cycle regulation genes for cancer to occur.
cancer incidence as you
in age
Multiple mutations in colorectal cancer
B.You may inherit mutations (from egg or sperm) that
increase your chances, but it’s not a guarantee of cancer.
i.e. breast cancer (5-10%), colorectal cancer (15%),
pancreatic cancer (10%)
***Recall that genes are made up of TWO alleles, one from
mom and one from dad. If one allele is functioning normally
and is dominant over the mutated (recessive) allele, you are
fine.
p53 = A a where a is mutant, p53 gene is fine
and will produce a normal protein.
But, if the dominant/normal allele acquires a mutation, then
that whole gene is mutated and will not properly function.
p53 = a a, the gene is defective and will not produce
a protein OR will produce a nonfunctional protein.
Viruses and Cancer
A.Viruses are linked to ~15% of all cancers. They insert
their DNA into yours, interfering with gene regulation
B. Examples – HPV (human papilloma virus) and
cervical cancer, Epstein-Barr virus (causes mono)
linked to lymphomas and nasopharyngeal cancers
IV.
Cell cycle controlled by cyclins and cyclindependent kinases (CDKs)
Slide 2
Some (not all) of the proteins (made by
your genes) that control the cell cycle Slide 2