Question

The protein products of tumour suppressor gene may
A. Be present in non-cancerous cells.
B. Cause signal cell death.
C. Regulate the cell cycle.
D. All of the above.

Answer 1

Hint: The tumor suppressor gene which is also called anti-oncogene is a gene that functions to regulate cell division and replication. If it gets inactivated or removed, it results in tumor formation as the cell will divide uncontrollably. Mutations result in the loss or inactivation of the tumor suppressor gene.

Complete answer:
The tumor suppressor genes are a group of genes that regulate cells during cell proliferation and replication. These are called anti-oncogenes as they function opposite to them. The tumor suppressor gene may cause signal cell death to control the proliferation rate whereas oncogenes do the opposite. The caretaker tumor suppressor gene types ensure the stability of the genome by repairing DNA if lethal mutations occur. The gatekeeper tumor suppressor gene types regulate cell growth. They either inhibit the cell cycle or cause apoptosis. Apoptosis is called signal cell death.
The proteins encoded by the tumor-suppressing genes are mainly involved in inhibiting cell proliferation. They control the gene expression of a particular stage in the cell cycle. They cause the cell to arrest in the cell cycle if DNA damage occurs. The non-cancerous cells or the ones that have normal cell cycle exhibit tumor suppressor genes. But the cancerous cells do not show the presence of tumor suppressor genes as they have been mutated or inactivated. Thus, from the above discussion, we can conclude that all enlisted options stand correct for the protein products of tumor suppressor genes.
So, option D is the right answer.

Note: A recently described tumor-suppressing gene category is called landscaper genes. These are involved in the regulation of the growth of cells by contributing to the surrounding niche. If these genes get mutated they alter the environment around the cell into a tumor-inducing environment. Thus, in a mutated state, they can promote unregulated proliferation.