Question

Q1)canser start when:

1:only tumor suppressor gene is mutated.

2:only proto-oncogene is mutated.

3:proto-oncogene and tumor suppressor gene are mutated at the sane time

4:proto-oncogene and tumor suppressor gene are not mutated at the sane time .

which is correct ?

Answer 1

Ans 1: Cancer is a condition where cells start proliferating uncontrollably and resulting in a mass of cells, called as tumour. These tumour cells when become aggressive, they start spreading to the other areas of the body via blood and initiate New tumour formation there itself. Then it is considered as cancer.

1. Only tumor suppressor gene is mutated, this may be  possible because tumor suppressor genes are essential genes which protect the cell becoming cancerous. They remain in active form and play essential role in keeping check on cell division and it's regulation.

If these genes get mutated, their function will get lost and this regulation of cell cycle and cell division will imbalance. Resulting in the uncontrolled cell division, leading to cancerous state.

But mutation only in the tumor suppressor gene, will not be itself initiate cancer.

2. Only proto-oncogene is mutated, not necessarily lead to cancer. As these proto oncogenes, are inactive form of gene and it's important for the cell that they remain inactive.

These genes when activated by exposure to some carcinogens, like gamma rays, X rays, superoxide radicals, causes again imbalance in regulation of cell cycle.

Gain of function of proto oncogenes by mutation will activate certain genes, That will allow irregular growth of cells. When only few mutation occur, cell try to repair that condition and prevent itself from becoming cancerous.

3 Proto-oncogene and tumor suppressor gene are mutated at the same time- When both these essential genes get mutated, then gain of function of proto oncogenes and loss of function of tumor suppressor gene due to mutation will disturb major events regulating cell cycle, with which cell may not be able to manage and will definitely become cancerous.

4 Proto-oncogene and tumor suppressor gene are not mutated at the same time, if no mutation will occur in any of these genes, cell will be under normal regulation of its cell cycle and will not become cancerous. But there are chances, other than these genes which can cause cancer. This is not the topic of this question.

These images will let you understand better,

DNA Proto-oncogene MUTATION DNA Oncogene Mutation DEREGULATED CELL DIVISION

Mutation inactivates tumor suppressor gene CELLS PROLIFERATE Mutation inactivates DNA repair gene Mutation of proto-oncogene creates an oncogene Mutation inactivates several more tumor suppressor genes CANCER

After, all these explanations, correct option is C- mutation in both tumor suppressor gene and proto oncogenes at the same time.

If still any doubt left, comment on this answer.