Answer Happy

Name: Proto-oncogenes include genes that stimulate the cell cycle. Proto-oncogenes can be mutated to become oncogenes, which stimulate the cell cycle too much. Whereas a proto-oncogene product is like a gas pedal that can be pushed or relaxed, an oncogene product is like a gas pedal that is stuck to the floor. Example of a proto-oncogene at the cellular level No mutant alleles One mutant allele 1) Look at the figure at right, which represents a typical proto-oncogene. At the cellular level, does it seem that mutations in protooncogenes generally act in a dominant or recessive manner? Explain briefly. 2) Look at the figure at right, with a typical tumor suppressor gene. Does it seem that mutations in tumor suppressor genes act in a dominant or recessive manner? Explain briefly. Normal cell division Mutation (usually gain-of-function) Tumor suppressor genes include genes that inhibit cell division under normal conditions. Many tumor suppressor gene products are like the brakes for cell division. When you think of the protein products of mutant tumor suppressor genes, think of having a car brake that is defective. Mutation (usually loss-of-function) Normal cell division Example of a tumor suppressor gene at the cellular level No mutant alleles One mutant allele Excessive cell proliferation Normal cell division Two mutant alleles Mutation (usually loss-of-function) in both alleles Excessive cell proliferation 3) The normal function of gene "X" is to kill cells that show signs of chromosome damage. Mutant forms of gene X are involved in cancer. Is gene X likely to be a proto-oncogene or a tumor suppressor gene? Why? 4) The normal function of gene "Y" is to signal for cells to divide when we need to heal a wound. Mutant forms of gene Y are involved in cancer. Is gene Y likely a protooncogene or a tumor suppressor gene? Why?