Question

In some of the cancer pictures tumor cells are scattered amongst surrounding normal tissue. Why is that significant?

What is an oncogene?  When it is mutated how does it contribute to uncontrolled cell division?

Answer 1

Ans: The phenomenon tumor cells surrounding normal cells and eventually penetrate normal cells is called invasion.The proliferation of transformed cells and the progressive increase in tumour size eventually leads to a breach in the barriers between tissues, leading to tumour extension into adjacent tissue. The tumor which is able to spread and invade surrounding tissues is known as malignant tumor and these type of tumor leads to cancer.Once these tumor cells proliferate enough they begin to form new blood vessels for themselves and this process is known as angiogenesis. Angiogenesis plays a critical role in the growth of cancer because solid tumors need a blood supply if they are to grow beyond a few millimeters in size.

An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels. These oncogenes are arises from the proto-oncogenes which are the part of the genome and a single mutation causes the proto-oncogenes to convert into oncogenes, so this type of mutation often termed as gain-of-function mutation. Proto-oncogenes involved in cell cycle and they positively regulate cell cycle and when they got mutated they can't able to do so and this leads to uncontrollable cell growth which eventually leads to cancer. Example of proto-oncogene is cyclin D which is a member of the cyclin protein family that is involved in regulating cell cycle progression. The synthesis of cyclin D is initiated during G1 and drives the G1/S phase transition. The G1/S transition is a stage in the cell cycle at the boundary between the G1 phase, in which the cell grows, and the S phase, during which DNA is replicated. So if Cyclin D gene mutated it is not able to differentiate whether cell is able to enter the S phase or not and this leads to destruction of cell cycle checkpoints and which eventually leads to uncontrollable cell division because of the corrupted cell cycle checkpoints and this eventually leads to tumor cells. So in this way mutation in proto-oncogenes leads to uncontrolled cell division.