Chapter 20, Problem 1A

Summary Introduction

Introduction:

The proto-oncogenes are proteins which are present in the normal cell. These proteins activate the process of the cell cycle and division leading to the proliferation of the cells. The tumor suppressor proteins inhibit the cell cycle and proliferation of the cells.

Answer to Problem 1A

Correct answer:

The proto-oncogenes are present inside the normal cells and initiate the process of cell cycle, division and mitosis. The tumor suppressor genes inhibit the process of cell division and proliferation of the cells. Therefore, option (d) is correct.

Explanation of Solution

Reason for the correct statement:

The proto-oncogenes synthesize a protein, which activates the process of cell cycle, proliferation and cell signaling. The tumor suppressor genes inhibit the process of cell cycle and proliferation.

Option (d) is given as “proto-oncogenes; tumor suppressor genes”.

“Normally in a noncancer cell, proto-oncogenes stimulate the cell cycle, and tumor suppressor genes inhibit the cell cycle”, it is the right answer.

Hence, option (d) is correct.

Reasons for the incorrect statements:

Option (a) is given as “tumor suppressor genes; oncogenes”.
The tumor specific genes inhibit the process of cell cycle and proliferation, whereas oncogenes activate the process of cell signaling in the cancerous cells. They are formed after the mutation of the proto-oncogenes. So, it is a wrong answer.

Option (b) is given as “oncogenes; tumor suppressor genes”.
The oncogenes activate the process of cell signaling in the cancer cells. The tumor suppressor cells inhibit the process of cell cycle proliferation and cell division. So, it is a wrong answer.

Option (c) is given as “proto-oncogenes; oncogenes”.
The proto-oncogenes are present in the normal cells and activate the process of cell cycle. The oncogenes are present in the cancerous cells and activate the process of cell signaling. So, it is a wrong answer.

Hence, options (a), (b) and (c) are incorrect.

Conclusion

The proto-oncogenes activate the process of cell division and cell proliferation in the normal cells, whereas the tumor suppressor genes inhibit the process of cell proliferation, cell cycle and division.