Biology 12
B6.4 Use examples to outline the roles of initiators and promoters in carcinogenesis.
Inquiry into Life, 7th ed.
pp. 480 – 481
Review "What Causes Cancer" up to, but not including, "Oncogenes: Normal Genes
Mutate" on pages 480 and 481.
Chemistry & Society, 5th ed.
pp. 417 – 422
Study the section entitled "Carcinogens" on pages 417 to 422.
Think about the example of initiation and promotion cited at the bottom of page 419.
Benzo()pyrene is an initiator of skin cancer in mice. It probably causes mutation of the
DNA in some of the skin cells. When croton oil comes into contact with the skin if
promotes cancer. The exact mechanism by which it does this is not known. Here are
some possibilities:
It may cause an additional mutation.
It may affect a regulator gene (i.e. ‘switch on’ a previously
mutated DNA strand, encouraging the rapid growth of mutant
cells.
It may suppress anti-oncogenes.
Can you theorize any other mechanisms?
Cigarette smoke (which contains many distinct chemicals) is thought to have some
substances which act as initiators and others which act as promoters.
Worksheet
Read the top half of the last page of the Cancer handout. Define initiator and promoter
and give examples of each.
(© 2004. C.K. Robinson, Summerland Community Learning Centre, School District No. 67)