Question

A) Explain how tumor suppressor genes like BRCA1 & BRCA2 prevent the development of cancer.

B) Explain how mutated BRCA1 & BRCA2 genes promote the development of cancer.

C) The average age of being diagnosed with cancer is 66. Why is it more likely for cancer to develop as a person gets older?

Answer 1

A. BRCA1 is a pleiotropic DNA damage response protein that functions in both checkpoint activation and DNA repair, whereas BRCA2 is a mediator of the core mechanism of homologous recombination. Both the proteins work in concert to protect the genome from double-strand DNA damage during DNA replication which may cause cancer or tumour development.

BRCA1 and BRCA2 are tumour suppressor genes. If one copy of either gene is mutated in the germ line, the result is hereditary breast and ovarian cancer which is inherited in an autosomal-dominant manner. This syndrome is associated with not only early-onset breast cancer but also an increased risk of ovarian, pancreatic, stomach, laryngeal, fallopian tube and prostate cancer.

B. Generally, BRCA1 and BRCA2 genes are the strongest susceptibility genes for breast cancer. Therefore, mutations in BRCA1 and BRCA2 genes are so effective in the increased risk for developing early-onset breast cancer and familial ovarian cancer, that mutations in these two genes are not only responsible for 90% of hereditary breast cancer cases and but also for the majority of hereditary ovarian cancer. Therefore, if either one of these two genes is damaged, damaged DNA will not be repaired, which can lead to more changes and more mutations in cell DNA and eventually lead to cancer.

C. cancer develops in older people simply because of their prolonged exposure to carcinogens such as sunlight, radiation, environmental chemicals, and substances in the food we eat. In addition, changes in tissues and organs with advancing age renders cells’ microenvironment more favourable to the development of cancer. Apart from these factors chronic inflammation, cancer-promoting DNA changes caused by oxygen free radicals, less-effective DNA damage-repair mechanisms, and weakening of the immune system are also responsible for cancer occurrence at old age.